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Solar methanol energy storage | Nature Catalysis
Abstract . The intermittency of renewable electricity requires the deployment of energy-storage technologies as global energy grids become more sustainably sourced. Upcycling carbon dioxide (CO 2 ) and intermittently generated renewable hydrogen to stored products such as methanol (MeOH) allows the cyclic use of carbon and addresses the challenges of storage energy density, size and transportability as well as responsiveness to energy production and demand better than most storage alternatives. Deploying this storage solution efficiently and at scale requires the optimization of production conditions to ensure predictable and maximum long-term process performance. Key to enabling this solution is the generation of highly productive syngas that is rich in carbon monoxide (CO) via reverse water-gas shift (RWGS) or solid-oxide electrolysis cell technologies. The focus herein is the RWGS reaction as it enables a solar-to-fuel efficiency of around 10% that can be deployable at a commercial scale. The need for a higher-efficiency route to renewable MeOH is discussed, and a comparative technoeconomic analysis of two solar-derived MeOH (solar MeOH) strategies is presented: the solar-CO-rich (based on the solar-RWGS process) and the solar-direct-CO 2 routes. You have full access to this article via your institution. Download PDF Download PDF Main . Renewable electricity, such as from solar-photovoltaics and wind sources, can be stored in many existing and emerging forms, as shown in Table 1 , and these include as potential, kinetic, chemical, thermal or magnetic energy, or as electric charge. Important considerations when choosing a storage option are the maximum power rating and lifetime, the storage capital expenditure (CAPEX) and operating expenditure (OPEX), various efficiencies, the storage duration and the geographical scope of end use. The global energy-storage market is expected to grow from 176.5?gigawatts (GW) in 2017 to nearly 1?terawatt (TW) by 2040 (an estimated US$620 billion invested) according to Bloomberg New Energy Finance 1 . Considering these huge storage demands, liquid fuels or power-to-liquid (PTL) systems are well placed as they enable the highest energy-storage potential. Other benefits include a long operating lifetime, the lowest storage cost, good energy density, excellent restitution efficiency, storage longevity, global scope and the potential to close the carbon cycle, albeit with an intermediate round-trip efficiency of ~35% (ref. 2 ). Table 1 Different types and examples of renewable energy storage a Full size table In 2019, air and sea transport, and the chemicals industry (excluding CO 2 stored in the chemicals themselves 3 ) contributed 5–6% (refs. 4 , 5 ) and ~14% (ref. 6 ) of global CO 2 emissions, respectively, that year (33?gigatonnes of CO 2 (GtCO 2 ) 7 ). These industries represent the current foremost candidates for decarbonization to keep below the 1.5?°C global-warming threshold by the year 2100 set by the Paris Agreement of 2015. Renewable MeOH is a contender PTL technology that can provide a cost-competitive alternative to traditional fossil-based feedstocks for these industries with an appropriate carbon tax in the near- to mid-term, and as a standalone technology in the mid- to long-term, with the current need primarily due to the higher costs associated with producing its feedstock hydrogen (H 2 ). Renewable MeOH also eliminates the high carbon intensity and sulfur emissions when replacing fuel oil as a marine fuel 8 and offers flexibility as a feedstock for ≥30% of industrial chemicals. In terms of the 2040 energy-storage expectations, to provide 876?terawatt-hours (TWh) (or a 10% capacity factor) would require a production capacity of 157?megatonnes of MeOH per year (Mt?MeOH?yr ?1 ) (based on the lower heating value of MeOH) or 43% more than generated by the current global MeOH industry 9 , which is an ambitious target. Finally, in the context of the broader transportation sector, the expanded use of MeOH in technologies such as indirect-MeOH fuel-cell (that is, MeOH-to-H 2 ) vehicles and direct-MeOH fuel-cell (or DMFC) vehicles (if issues related to crossover and water retention can be solved 10 ) may also become commercially viable as large markets, such as California and the European Union, transition away from fossil fuels 11 . Benefits of power-to-liquid systems . A high H 2 density can be realized in its liquid state, but it is only 53% of the volumetric energy density of MeOH 12 . Moreover, MeOH contains 40% more hydrogen mass density (kg?H 2 per m 3 ) than liquid H 2 . Further challenges with H 2 include requiring cryogenic temperatures for its storage and that it typically vents 1–5?wt% each day 13 . More energy is expended during compression and liquefaction, typically 10–15% and 30–40%, respectively, of the energy contained in the H 2 (ref. 13 ). Its low density makes transporting H 2 another limiting factor 14 . The post-2025 US Department of Energy (USDoE) target for on-board hydrogen storage is 2.1?kWh per kg system, with current 70?MPa compression at 1.4 (ref. 15 ). Light magnesium-based hydrides (or MgH 2 ) can theoretically achieve 2.5 and are the basis of the one-time-use hydrogen-based fuel Powerpaste that has recently been introduced by the Fraunhofer Institute 16 . However, challenges of most hydride/complex-hydride systems are the high kinetic re-/dehydrogenation barriers and poor reversibility whereby various techniques have been applied with some success 14 . Therefore, it is preferable to transform H 2 at the source into higher-energy-density MeOH, which can be later transported and converted into electricity, transported and used directly or steam reformed to H 2 (ref. 17 ), transported and transformed into value-added chemicals/precursors (for example, formaldehyde, acetic acid, olefins and solvents) or transformed into higher-value e-fuels or renewable-electricity-derived fuels (for example, dimethyl ether, dimethyl carbonate, oxymethylene dimethyl ethers and e-jet or e-kerosene) 16 . Hydrogen-generating technologies . Intermittent, distributed-H 2 water-electrolysis and water-splitting technologies include alkaline water electrolysis (AWE), polymer electrolyte membrane (PEM) electrolysis, solid-oxide electrolysis cells (SOECs), photo-electrochemical and photo-catalytic water splitting and solar-thermochemical cycles 18 . It is anticipated that centralized-H 2 generation technologies such as nuclear thermochemical cycles (NTCs) will also become more appealing in the future. At present, the most affordable route to H 2 remains steam methane reforming (SMR), which costs US$1,750?t?H 2 ?1 (all in 2020 dollars) and has a thermal-to-H 2 efficiency (T2HE) of 71% (ref. 18 ) for a primary energy demand (PED) of 9.3?MWh heat ?t?H 2 ?1 (SMR plus RWGS heat of reaction at 800?°C). In this section we take a snapshot of a few leading H 2 -generating technologies for providing the H 2 feedstock for MeOH synthesis. For reference, the theoretical liquid water-splitting energy requirement is ~39.6?MWh elec ?t?H 2 ?1 . Alkaline water electrolysis . AWE uses an aqueous alkaline electrolyte of ~30% KOH or NaOH and operates at 80–90?°C and at a pressure of 2.5–3.0?MPa (ref. 18 ). The feed water needs to be pure (conductivity?electrode materials (cathode: Pt/Ni, anode: metal-oxide-coated Ni) are generally less expensive than PEM platinum metal group catalysts, and AWE offers high durability due to the exchangeable electrolyte. AWE has a system efficiency (power-to-H 2 ) of 63–73% (ref. 18 ) or a PED of 53.8–62.4?MWh elec ?t?H 2 ?1 . The primary challenges of this technology are crossover issues of H 2 and O 2 through the semi-permeable diaphragm 18 , a low current density due to high ohmic losses (necessitating large system areas for high production volumes) 18 , identifying lower-cost and durable electrode materials, and the need for ample electricity use that accounts for up to 75–80% of the H 2 cost. Deployment of lower-cost electricity will offset the last of these, and the National Renewable Energy Laboratory (or NREL) estimates that the future (2025) minimum selling price of H 2 ( \({\mathrm{MSP}}_{{\mathrm{H}}_{2}}\) ) via grid-AWE (or all net present costs over the process lifetime excluding compression, storage and dispensing) will be US$4,290?t?H 2 ?1 (2020 dollars) 19 , with future capital costs expected to drop. Polymer electrolyte membrane electrolysis . PEM cells feature a thin (<0.2?mm) perfluorosulfonic acid polymer membrane such as Nafion and precious-metal electrodes (iridium, platinum, rhodium and ruthenium) 18 . The supplied water must be especially pure (<1?μS?cm ?1 ) and this technology is more compact and can achieve a higher current density than AWE. Other less expensive electrode materials are being sought to make this technology more affordable. The USDoE is forecasting future total electrical usage for a PED of ~50?MWh elec ?t?H 2 ?1 at an expected future (2025) cost of US$5,240?t?H 2 ?1 (2020 dollars) 20 . This type of electrolysis was used for the solar strategies discussed herein at this optimum PED. Solid-oxide electrolysis . SOECs use steam for H 2 and have an electricity demand that is less 21 , 22 than AWE with a system efficiency of ~85–90% (ref. 18 ) at temperatures of up to 1,000?°C. The resulting PED is 28.9–33.3?MWh elec ?t?H 2 ?1 (assuming that another energy source is supplied to produce the feed steam) with a T2HE of 35–45% (when using nuclear heat with a heat to electricity efficiency ( η HE ) of 45%) 21 , 21 or 47–60% (when using a natural gas-CHP plant (NG-CHP) with an efficiency η HE of 60%) at 800?°C. Current issues with their mass deployment are the limited lifetime of the fuel electrode (due to SiO 2 poisoning and redox instability 23 ) and the oxygen electrode (due to chromium poisoning and delamination 23 ), the limited long-duration performance of the cell stacks (a state-of-the-art co-electrolysis (steam plus CO 2 ) degradation rate of 1.7% per 1,000?h for 3,600?h at ?1?A?cm ?2 (ref. 23 )), the complexities of stack cracking due to steam condensation 23 and the expensive manufacture and assembly of large-area generating cells for commercial plants 22 . Haldor Topsoe has commercialized a 50?kW (capacity for ~0.0022?kg?MeOH?s ?1 ) SOEC unit in Foulum, Denmark, which has a system efficiency of 95.9% and a T2HE of 58% (assuming an NG-CHP η HE value). Likewise, the NREL estimates that the future (2030) \({\mathrm{MSP}}_{{\mathrm{H}}_{2}}\) via nuclear-coupled SOEC will be US$3,880?t?H 2 ?1 (2020 dollars) 19 , with electricity and thermal energy being the largest expenses. Nuclear thermochemical cycles . For producing H 2 , NTCs coupled with generation-IV nuclear reactors have the advantage of primarily using high-grade heat (~1,000?°C) in addition to electricity (overview: 21 , 24 detailed: 22 , 25 ). Hundreds 24 of NTCs have been theorized, which take advantage of the incredible energy density of nuclear fuel (~22?GWh heat per kg?uranium-235 or a 1?cm 3 UO 2 pellet can provide H 2 for eight fuel-cell vehicles to cover the breadth of the continental United States 25 ). One especially promising NTC is the Hybrid Sulfur (HyS) process, which uses an electrochemical step to improve the inefficient low-temperature regeneration of H 2 SO 4 from SO 2 ?+?2H 2 O, releasing H 2 (ref. 22 ), and is a high priority for the USDoE with a theoretical T2HE of 50% and a PED of 66.6?MWh total ?t?H 2 ?1 (ref. 22 ). It uses only ~25% of the electrical requirement of low-temperature water electrolysis for the low-temperature electrochemical step (~12?MWh elec ?t?H 2 ?1 ), with the remainder being high-grade heat. El-Emam and ?zcan 21 found that the HyS NTC process was more economical than an equivalently sized SOEC process, producing H 2 at a 20% discount due to the lower capital cost and electricity demand of the HyS process. As soon as generation-IV reactors come online the cost is expected to be ~US$2,290?t?H 2 ?1 (ref. 21 ) or slightly above that of SMR. Carbon dioxide capture technologies . A technology-neutral approach for ranking the sustainability of upcycled CO 2 e-fuels will emphasize their carbon intensity (CI) 8 , 26 . As defined by the US Energy Information Administration, the CI is the amount of net carbon by weight emitted per unit of fuel energy consumed. Direct-air capture (DAC), that is, capturing CO 2 from the atmosphere (~0.04%), is currently the most energy-intensive source of CO 2 but provides the lowest e-fuel CI value. Hence, in this section we highlight two promising DAC technologies and related disruptive innovations. Alkali aqueous capture . The company Carbon Engineering recently detailed 27 their ~1?tCO 2 ?yr ?1 DAC pilot process that consumes 1.54–1.82?MWh total ?tCO 2 ?1 for their two combined heat and power scenarios. In the low- and high-cost scenarios for producing a 97% CO 2 product gas, the pressure and costs were 0.1? \({\mathrm{MPa}}_{{\mathrm{CO}}_2}\) and US$97–134?tCO 2 ?1 , and 15.1? \({\mathrm{MPa}}_{{\mathrm{CO}}_2}\) and US$116–168?tCO 2 ?1 , respectively. The current operation uses 5–20% electricity and the balance is from high-grade NG heat (peak 900?°C). The capture system consists of an aqueous potassium hydroxide cross-flow contactor and a secondary lime loop that forms calcite, which is calcined to yield CO 2 . Various engineering innovations have been realized including forming calcium carbonate pellets in a high-ionic-strength solution, reducing alkali ‘drift’ from the contactor, using an oxygen-fired calcination reactor and slaking the lime with steam. A challenging aspect of this capture technique is the high water consumption, requiring 4.7?t?H 2 O?tCO 2 ?1 . With seawater desalination the authors estimated an additional cost of ~US$5.2?tCO 2 ?1 . Emissions for the high-cost scenario are expected to be ~0.12?tCO 2 per tCO 2 captured with a 0.3?tCO 2 ?MWh ?1 grid intensity, and with improved net emissions and affordability attainable via further renewable electrification. After economic considerations, a practical minimum size of this process was determined to be ≥0.1?MtCO 2 ?yr ?1 . Disruptive electrochemical technologies that process the CO 2 sorbent solution (containing carbonate and bicarbonate ions) directly to produce CO have also been proposed 28 and have shown a comparable PED (~6.9?MWh elec ?tCO ?1 ) to the SMR process (~7.9?MWh heat ?tCO ?1 ), where the former would benefit from low-cost renewable electricity. Supported amine capture . The advantage of the monoethanolamine (MEA) capture medium is that it involves a chemical reaction to form a carbamate species according to equation ( 1 ): $${{{\mathrm{CO}}}}_2 + 2{{{\mathrm{R}}}}_1{{{\mathrm{R}}}}_2{{{\mathrm{NH}}}} \leftrightarrow \left[ {{{{\mathrm{R}}}}_1{{{\mathrm{R}}}}_2{{{\mathrm{NCO}}}}_2^ - + {{{\mathrm{R}}}}_1{{{\mathrm{R}}}}_2{{{\mathrm{NH}}}}_2^ + } \right].$$ (1) The reaction enables use with dilute DAC streams, and the amine loading is typically 20–30?wt% in water with a capacity of 0.4?tCO 2 ?t?MEA ?1 (ref. 18 ). Challenges of the aqueous amine process are the high energy cost of regenerating the large quantities of solvent, corrosiveness 29 , the low process pressure and the low MEA degradation temperature 18 . Supported amine sorbents avoid thermal-cycling large quantities of water, and the sorbent capacity is expected to improve tenfold from current capacities 30 . The sorbents can be supported via physical loading, by being covalently linked to the support, or by in situ polymerization of aminopolymers 18 . The company Climeworks uses a unique cellulose fibre supported by amines 31 with a DAC PED of 1.7–2.3?MWh total ?tCO 2 ?1 (12–15% electricity and the balance being low-grade ~100?°C heat) 30 that also co-captures water at a rate of 0.8–2?t?H 2 O?tCO 2 ?1 . Emissions are ~0.1?tCO 2 per tCO 2 captured 32 and the target capture cost is ~US$90?tCO 2 ?1 for large-scale plants 30 . A current disadvantage is the protracted full-cycle time of 4–6?h. Similar challenges to the aqueous process are thermal stability, and new challenges include solid material handling, and fouling and degradation, either over many cycles or in the presence of contaminants (for example, SO 2 ) 18 . Disruptive solid absorption technologies include Global Thermostat’s aminopolymer system with a full-cycle time of less than 30?minutes and a DAC PED of 1.3–1.7?MWh total ?tCO 2 ?1 (11–16% electricity with the balance being 85–95?°C heat). The projected cost is ~US$15–50?tCO 2 ?1 (ref. 30 ). For an in-depth discussion of these DAC technologies in the context of mass deployment please see Realmonte et al. 33 . Other disruptive innovations that may gain traction in the future are organic polymer nanomembrane CO 2 capture or membrane-based DAC technology 34 . Producing CO-rich syngas from carbon dioxide . RWGS chemistry, as shown in equation ( 2 ), was first observed by Carl Bosch and Wilhelm Wild in 1914 (ref. 9 ) and can be used to transform CO 2 into high-performance CO-rich syngas. $${{{\mathrm{CO}}}}_2 + {{{\mathrm{H}}}}_2 \leftrightarrow {{{\mathrm{CO}}}} + {{{\mathrm{H}}}}_2{{{\mathrm{O}}}}\quad {\Delta}{{H}}_{298\,{{{\mathrm{K}}}}} = + 41.3\,{{{\mathrm{kJ}}}}\,{{{\mathrm{mol}}}}^{ - 1}$$ (2) The main challenge for this reaction is the characteristically high temperature (≥700?°C) needed for adequate CO 2 conversion ( \(X_{{\mathrm{CO}}_2}\) ) (67 and 44% at 700?°C with a 3:1 and 1:1 H 2 :CO 2 feed, respectively, on a dry basis from Fig. 1b ), necessitating the consideration of concerted technology such as concentrated solar energy (which is favourable for regions such as Australia, the Middle East and North Africa 8 ) for renewable production. New processes that avoid separating CO:CO 2 mixtures have also been discussed 35 . Thermochemical metallic-phase catalyst components include noble metals gold 36 , palladium 36 , platinum 37 , 38 , rhodium 37 , 39 and ruthenium 36 , and more cost-effective earth-abundant metals, cerium 38 , copper 37 , 38 , iron 38 , molybdenum 38 and nickel 37 , 39 , while photochemical and/or photothermal and solar-indium-based RWGS catalysts that use renewable solar energy are reviewed in refs. 9 , 40 , respectively. Supports for the metallic phases may provide morphological, lattice strain, electronic (strong metal–support effect) and sintering resistance and can provide interfacial active sites or oxygen vacancies that are all critical to the functioning of the catalysts. In view of this, efforts to engineer multicomponent materials that have good product selectivity and catalyst stability at moderate to high temperatures are ongoing 9 , 36 . Examples of RWGS catalysts are shown in Fig. 1a . The equilibrium CO yield on a dry basis as a function of the temperature is shown in Fig. 1b . Fig. 1: Key metrics and figures for RWGS technology incorporation. a , RWGS catalyst cost versus performance. Note: ZnAl 2 O 4 (ref. 81 ) and Ni/Al 12 O 19 (ref. 3 ) (arrow indicates in the 10 –5 –10 –6 range) assumes US$ catalyst per kg CO and one year of operation (P-, pilot scale (~kg catalyst quantity) tested). b , RWGS equilibrium yield as a function of temperature. c , RWGS temperature with a 6:1 H 2 :CO 2 feed as a function of the recycled CO 2 ?+?CO?+?H 2 percentage for a constant product CO:CO 2 ratio of 10:1. Panel a adapted with permission from ref. 56 , RSC. Panel b reproduced with permission from ref. 9 , Wiley. Full size image RWGS and SOEC energy demand and efficiencies . In our work 9 we estimated the cost of operating a solar-RWGS unit using a Ni/Al 12 O 19 catalyst 37 (Fig. 1a ) at 750?°C and 0.1?MPa with 100% CO 2 conversion and CO selectivity ( S CO ). On re-evaluation, near-complete one-pass conversion (~91%) would require a higher temperature of ≥1,050?°C (ref. 3 ) with 6:1 H 2 :CO 2 (refs. 3 , 41 ), resulting in a CO:CO 2 ratio of 10:1, necessitating H 2 removal for a suitable stoichiometric number (SN) or a measure of the redox quality of a gas of 2.05 (for example, commercial membrane technology: pressure swing adsorption or the VaporSep-H 2 process (Membrane Technology and Research) can remove 70–95% of the feed H 2 ). Another option to obtain a high CO:CO 2 ratio is to start with 3:1 H 2 :CO 2 at 1,050?°C (one-pass \(X_{{\mathrm{CO}}_2}\) : 83%) resulting in a CO:CO 2 ratio of 3.75:1 and thereafter remove the excess CO 2 (for example, the Polaris membrane (Membrane Technology and Research) can remove ~80% of feed CO 2 ). Similarly, one could recycle a portion of the product CO 2 ?+?CO?+?H 2 as shown in Fig. 1c , which would lower the maximum temperature needed for optimum syngas production, assuming that an adequate CO selectivity could be maintained at the lower temperature. Notably, however, the higher temperature and material considerations are already similar to many commercial processes, that is, SMR, pyrolysis, gasification and so on, and a high RWGS temperature was found to be better overall for process economics 42 , 43 . Interestingly, higher operating temperatures lead to lower solar-RWGS energy requirements due to the lower heat of reaction (31.7?kJ per mol CO at 1,050?°C) with complete latent heat recovery. At the adjusted conditions (1,050?°C and 6:1 H 2 :CO 2 ) and with a solar-to-CO efficiency (or T2COE) of 70%, the PED RWGS is 0.45?MWh solar ?tCO ?1 . Supplying the requisite 0.072?t?H 2 ?tCO ?1 from the PEM water-electrolysis unit requires an additional 22.5?MWh solar ?tCO ?1 (with a solar-to-power efficiency ( η solar-to-power ) of 16%) of primary energy (providing one-third of the produced H 2 for RWGS) for a final PED RWGS,total of 22.9?MWh solar ?tCO ?1 or 20.1?MWh solar ?t?MeOH ?1 . It is instructive to compare the RWGS energy demand with Haldor Topsoe’s proposed 300?kW SOEC (CO 2 → CO?+??O 2 , with a capacity for ~0.04?kg?MeOH?s ?1 ), which has an estimated system efficiency ( η power-to-CO ) of ~92.1% and a T2COE of ~55.3% (using NG-CHP electricity). The PED SOEC,elec is estimated to be 1.95?MWh elec ?tCO ?1 (or a heat of reaction of 180.7?kJ per mol CO at 900?°C) 44 . The energy incorporation efficiency (EIE CO ) metric determined from our work 9 , a metric that considers the fossil energy input and must be positive for a renewable product, is 100% for solar-RWGS and ?15.2% for NG-SOEC. In prospect, if SOEC could scale economically, avoid degradation at operating conditions and be powered using solar-photovoltaic electricity, the PED total would be a noteworthy 12.2?MWh solar ?tCO ?1 . RWGS avoids some of SOEC’s shortcomings through its low CAPEX and OPEX (contributing only 2% to the solar MSP MeOH or US$300?t?MeOH ?1 ), high capacity (≥1?kg?MeOH?s ?1 ) and projected 30?year operating life. In terms of the CO feedstock cost, RWGS would be competitive with the fossil CO market price (US$300?tCO ?1 (ref. 44 )) with renewable electricity prices of ≤US$0.082?kWh ?1 . CO-rich methanol synthesis process improvements . The benefits of CO-rich syngas compared with direct-CO 2 are twofold: the catalyst and the process. Both strategies used the commercial copper–zinc oxide–alumina (CZA) catalyst. The MeOH catalyst benefits are that the synthesis avoids multivariable deactivation including water deactivation via hydroxylation of the commercial CZA’s ZnO phase 45 , a notable challenge for direct-CO 2 processes 46 , 46 , especially the loss of active sites with CZA-type catalysts 47 . The process benefits of CO-rich syngas are manyfold and include the following: (1) it allows a higher thermodynamic equilibrium yield to MeOH, (2) the MeOH selectivity can reach 100% with as little as 5% CO in the feed (at 250?°C, 8?MPa, and gas hourly space velocity (GHSV) of 9,900?h ?1 (ref. 48 )) and (3) it accelerates 9 the rate of reaction allowing for higher GHSV values and the associated CO x conversion. For example, for near-equilibrium conversion using a fresh CZA catalyst, the GHSV attainable for a CO-rich feed (29:2.85:68.15% CO:CO 2 :H 2 ) versus a direct-CO 2 feed (25:75% CO 2 :H 2 ) is 9,900?h ?1 versus 493?h ?1 for an amount of CO x converted of 63.0% versus 30.1% at these rates of throughput 49 . Alternatively, comparing the MeOH space-time yield (STY MeOH ) at the same GHSV (9,900?h ?1 from our study 50 ) results in a large variation in performance of 2.83 versus 0.47 kg?MeOH per litre catalyst per hour for a CO-rich versus a direct-CO 2 feed, respectively. The effect of benefit (3) results in further benefits: (4) a higher per-pass conversion and a smaller reactor footprint and recycle stream, which can save substantial compression costs; (5) the higher MeOH yield (32% versus 8.8% for CO-rich versus direct-CO 2 feeds) reduces the need for high-energy input for multistage separation to obtain a MeOH quality of American Society for Testing and Materials (or ASTM) grade AA purity (99.85?wt% MeOH) or better 51 , avoiding costly water separation; and finally (6) the RWGS avoids wasting 33% of the H 2 feed that is energy-intensive to produce. Water removal post-RWGS is essential to gain these benefits. Nevertheless, research continues on the direct-CO 2 route, with catalysts developed thus far exhibiting marginal STY MeOH values in the range of 0.4–0.8 at commercial GHSV values of 8,000–10,000?h ?1 (refs. 51 , 52 ). A thorough analysis of various energy-storage options (H 2 , CH 4 , MeOH and NH 3 ) in ref. 2 identified that even the lower-performance direct-CO 2 route was the most cost-competitive, which improves further for CO-rich MeOH production. Shifting the equilibrium yield forwards by removing products in situ is yet another way to improve the MeOH yield 53 ; however, these semi-continuous gas-in liquid-out designs based on forced-convection condensation remain at the demonstration stages only. Metrics of solar methanol strategies from technoeconomic analysis . Two MeOH synthesis efficiency metrics were determined from our work 9 : EIE MeOH (previously described) and the primary efficiency ( η primary ), the ratio of the product chemical energy to the total PED (including solar energy). Comparing the solar-CO-rich, solar-direct-CO 2 and commercial strategies (Strategies A:C:Traditional from ref. 9 ), the EIE values are ~57, 53 and ?86% and the η primary values are ~9.5, 7.7 and 54%, respectively, with the solar strategies being comparable due to buffering by the major contribution to the energy demand, that is, H 2 production. The differences for the solar strategies are that 9% less overall fossil energy input (for the MeOH purification section) and 20% less overall solar-energy input are needed (for the more efficient MeOH synthesis scheme that consists of the MeOH reactor, the flash tank and the recycle loop) per tonne of MeOH, which give a resulting synthesis section PED total of 4.7 (solar-CO-rich) versus 21.4 MWh solar ?t?MeOH ?1 (solar-direct-CO 2 ). The total fossil emissions avoided for the solar-CO-rich and solar-direct-CO 2 strategies compared with the commercial strategy were ?77 and ?74%, respectively. Moreover, the round-trip efficiency provides a convenient metric for comparing the solar-PTL strategies with other energy-storage options, and are estimated as ~25% and 20% for the solar-CO-rich and solar-direct-CO 2 strategies, respectively, assuming the best-case DMFC efficiency of 40%. Finally, Stechel and Miller’s insightful contribution 54 revealed that a solar process with a solar-to-fuel efficiency η solar-to-fuel of ≥10% (≈? η primary ) is about the minimum efficiency required if the practical scaling and mass deployment of this technology are to have a chance of competing on a cost basis with fossil fuels. For the solar-CO-rich, solar-direct-CO 2 and fossil-based commercial strategies we found 9 MSP MeOH values of ~US$1,500, 2,000 and 300?t?MeOH ?1 , respectively, which is consistent with other studies 52 , although in a different study 55 thermal-direct-CO 2 was found to be somewhat higher at US$2,650?t?MeOH ?1 (at a comparable capacity of 100 versus 86.4?t?MeOH?d ?1 in this study). Solar-TC water/CO 2 splitting (at ≥450?°C higher than RWGS) is becoming increasingly competitive with an MSP MeOH of US$4,700?t?MeOH ?1 (ref. 9 ). The PED total for solar-CO-rich, solar-direct-CO 2 and fossil-based commercial technoeconomic analysis (or TEA) strategies were 67.2, 83.3 and 11.9?MWh total ?t?MeOH ?1 . Extending our analysis to the situation where all H 2 could be supplied from NTCs, the PED total for the solar-CO-rich and solar-direct-CO 2 strategies would become a noteworthy 12.6 and 29.3?MWh total ?t?MeOH ?1 , respectively, the former almost on a par with the energy demand of the commercial strategy. In terms of renewable electricity use, the solar-CO-rich strategy uses 10.3 MWh elec t MeOH –1 on the higher performance end of typical renewable-electricity-derived MeOH (or e-MeOH) plants 8 . For detailed assumptions of the TEA analysis the reader is kindly referred to ref. 9 . Status of RWGS technology . An upstream RWGS process in tandem with a Fischer–Tropsch liquid (FTL) reactor or a MeOH synthesis reactor is an established concept 3 , 39 , 42 , 56 , 57 , 58 ; however, it has yet to be demonstrated at scale. In one study 58 , the authors envisaged a biogas-fired thermochemical-RWGS unit to obtain FTLs from anaerobically digested sewage sludge, with a 3:1 H 2 :CO 2 feed, a ZnAl 2 O 4 catalyst at 650?°C and pressure swing adsorption for H 2 removal. The authors found that economies of scale benefitted the price: going from 1 to 1,670?tonnes of FTL per day the price reduced from US$22 to US$1.5 per litre of FTL or to within twice the commercial fossil-based price, supporting the case for centralized PTL energy storage. A recent pilot study 56 demonstrated a thermochemical-RWGS unit (conditions: 450?°C, 2.1?MPa, GHSV 1.7?litres per kg per s, ~1?kg of K-Mo 2 C/γ-Al 2 O 3 catalyst, ten days on stream, \(X_{{\mathrm{CO}}_2}\) 71%, S CO 95%, CO:CO 2 = 3.2:1 with a H 2 :CO 2 feed of 3:1 and a recycle ratio of 1) with a catalyst cost similar to CZA (shown as Cu-ZnO/Al 2 O 3 ) and a performance approaching that of a noble-metal catalyst, as shown in Fig. 1a (as K-Mo 2 C b ). The less than ideal S CO at higher recycle ratios nevertheless allowed single-pass operation for downstream MeOH production (SN?≈?2). A few catalysts had a lower cost although they had up to only half the performance, with this catalyst being a good candidate for scale-up if the selectivity issues can be resolved. While scaled-up systems remain scarce, RWGS has also been investigated by Zubrin et al. 59 in combination with the exothermic Sabatier reaction for the production of rocket-propellant products (at around 1?kg?d ?1 , ~2:1 O 2 :CH 4 ) for Mars in situ water/CO 2 resource utilization. The operating conditions are milder (~400?°C with recycling) consuming 21.6?MWh elec per tonne product (unoptimized) with H 2 recycled. Owing to the RWGS reaction being faster than FTL reactions (160-fold at 902?°C and 3?MPa versus 233?°C and 2.5?MPa (ref. 3 )) and MeOH synthesis reactions (between five- and tenfold under the same conditions, 160–240?°C, 0.6?MPa, 1:1 CO:CO 2 (ref. 60 )), the envisaged commercial-scale RWGS unit is expected to be a compact device 3 . Comparing process developments of direct-CO 2 versus CO-rich . Although the trend is towards direct-CO 2 MeOH synthesis, it is worth comparing and contrasting the thermal-direct-CO 2 process developments with the solar/thermal-CO-rich process. The company Carbon Recycling International operates the famed renewable thermal CO 2 -to-MeOH George Olah plant in Reykjavik, Iceland using AWE-derived H 2 with recent expansion interest in Norway and China. The notable developments 61 are (1) there are fewer by-products, which allows fewer low-efficiency (5–10%) fractionation trains, (2) the reaction is less exothermic, leading to lower-cost reactors using milder conditions and (3) the lower exothermicity of the reaction enables less catalyst sintering. These developments, although noteworthy, ignore notable drawbacks that include (1) a lower STY MeOH and higher recycling energy and costs, (2) a lower MeOH selectivity due to the RWGS side reaction, (3) the need for increased heat integration as there is less waste heat available and that (4) when comparing the costs, the MSP MeOH of the Olah plant is similar to the commercial MSP MeOH albeit with concentrated CO 2 capture from the adjacent geothermal plant as well as Iceland’s renewable (75:25% hydrothermal:geothermal) and low-cost business electricity rate (US$0.048?kWh ?1 ) for H 2 generation, with the primary disadvantage being the process water-separation costs. Controlling the reaction exotherms is an ongoing optimization for CO-rich MeOH production to avoid hot-spots and catalyst sintering, with technologies such as modular microreactors that have higher heat-transfer coefficients than conventional reactors (by around an order of magnitude) 62 addressing some of these issues. CO does introduce safety hazards, but overall the reactor footprint is reduced and plentiful medium-grade heat is available for electrolysis cells, DAC systems, preheating and fractionation trains. When comparing the contribution of the H 2 cost to the solar-CO-rich versus solar-direct-CO 2 strategies, we found it to make up 80% versus 60% of the MSP MeOH at the current photovoltaic-PEM cost of US$10,970?t?H 2 ?1 . If current solar-to-electricity prices (US$0.14?kWh ?1 ) decrease to fossil-electricity prices (US$0.06?kWh ?1 ), then parity between the solar-CO-rich and commercial strategies could be realized with a carbon tax of US$210?tCO 2 ?1 . Thus, it is expected that expanded H 2 sourcing flexibility, further renewable electricity affordability and solar-to-power efficiency improvements will be more beneficial to the solar-CO-rich process. Finally, catalyst deactivation, due to high amounts of water for direct-CO 2 processes, and the lifetime costs of refurbishment/disposal of rare-element catalyst components require further study, although companies like Clariant expect multistage reactor technology with interstage condensation to mitigate these disadvantages somewhat 63 . Simulating CO-rich methanol energy-storage catalyst performance . Using the kinetics model of Vanden Bussche and Froment 64 (validated in our work 9 ) under commercial operating conditions of 250?°C and 8?MPa, and for a GHSV of 9,900–40,000?h ?1 , MeOH PTL production data were derived. This model has recently been revisited 65 with new techniques and proved to be resilient. The model uses a fresh commercial Synetix 51-2 CZA catalyst with a feed-gas composition of 2.85:29.00:68.15?vol% CO 2 :CO:H 2 (CO:CO 2 10:1 and a 2% CO 2 maximum conversion point 66 ) at the optimal SN of 2.05. The simulated operation was a one-dimensional plug flow, isothermal, with no heat or mass transport limitations, isobaric and with negligible impurities. Therefore, the model approximates the ideal performance of a dynamic MeOH energy-storage system shown in Fig. 2a . Deactivation was simulated in the model by successively reducing the amount of active catalyst at constant GHSV. Fig. 2: MeOH energy-storage scheme and performance. a , MeOH energy-storage layout and consumer applications, top-left table data summarize the energy demand per tonne MeOH and specific unit data beneath the illustrations summarize the energy demand for each specific chemical product produced. b , MeOH yield ( Y MeOH ) and STY MeOH as a function of the amount of active CZA catalyst. The model uses a high-performance CO-rich feed of 2.85:29.00:68.15?vol% CO 2 :CO:H 2 . c , Deactivation profiles based on equation ( 3 ) and a 250?°C operating temperature for the CZA catalyst. The t o values correspond to different starting deactivation times where the activity is normalized to 1.0. Full size image It is confirmed here that under ideal conditions the commercial catalyst may experience considerable deactivation (85–95%) to achieve the long-term STY MeOH commercial production target of ~1?kg MeOH per litre catalyst per hour (ref. 67 ). Figure 2b presents the deactivation data at the two GHSV limits that bound the typical commercial process 66 , 68 . The yields and STY MeOH values decrease monotonically as expected with catalyst deactivation. In actual operation, a process optimization of a higher separation cost versus a slightly more productive catalyst is necessary before the STY MeOH values ultimately converge at high deactivation. Predicting the long-term CO-rich MeOH energy-storage performance . The performance data (derived above) can now be compared with the long-term commercial catalyst deactivation profile. Rezaie et al. 69 presented a well-studied deactivation model for the CZA catalyst, as shown in equation ( 3 ), $$\frac{{{\mathrm{d}}a}}{{{\mathrm{d}}t}} = - K_{\mathrm{d}} \, {{{\mathrm{exp}}}}\left( {\frac{{ - E_{\mathrm{d}}}}{R} \left( {\frac{1}{T} - \frac{1}{{T_{\mathrm{R}}}}} \right)} \right) a^5$$ (3) where T is the reactor/catalyst operating temperature (K), t is the elapsed process time (h), R is the universal gas constant (8.314?J?mol –1 ?K –1 ), T R is the reference temperature (513?K), E d is the deactivation activation energy of the CZA catalyst (91,270?J?mol ?1 ), K d is the deactivation constant of the CZA catalyst (0.00439?h ?1 ) and the variable a denotes the exposed metallic surface area 70 . This deactivation equation is exclusively a function of the reactor operating temperature 71 , an approximation for CO-rich syngas 72 , 73 . A plot of the CZA catalyst deactivation extent at 250?°C is shown in Fig. 2c on a timescale of 4,000?h (~165 days or 12.7% of a typical CZA catalyst’s lifetime). A comprehensive summary of power-law deactivation models can be found in ref. 66 . A sensitivity analysis on the onset of deactivation (with the associated initial activity normalized to 1.0) changes the final deactivation fraction marginally. At ~10,000?hours (1.14 years), which is ~32% (at 90% capacity factor) of the catalyst’s lifetime, the medium-level (Fig. 2c ) deactivation extent is 90% at a GHSV of ~9,900?h ?1 . At this point the MeOH yield and STY MeOH value are ~6.3% and ~0.79. What is evident from this analysis is that even after around one-third of the rated catalyst operating lifetime, the solar-CO-rich PTL option remains more productive compared with the fresh solar-direct-CO 2 energy-storage option. Around this time, the catalyst operating conditions such as temperature, pressure and GHSV are modified to maintain the MeOH activity. To achieve this optimum outcome, reactor technology will need to meet the peak thermal challenges of mid- to large-scale reactors. Present and future outlook . Solar-derived CO-rich syngas from CO 2 could provide long-term, well-defined, efficient and energy dense MeOH energy storage that can be engaged as an energy-supply buffer for intermittent renewable electricity or used for consumer applications. The original electrical energy can be recovered from the MeOH product with a round-trip efficiency of 25%, which is suitable for long-duration storage, and with η solar-to-fuel ?≈?10% (≈? η primary ), which makes it competitive for scaling up to commercial levels. A carbon tax of US$500?tCO 2 ?1 would today allow cost parity between the solar-CO-rich strategy (based on RWGS) and the fossil-based commercial process, improving to US$210?tCO 2 ?1 with future advances in renewable energy efficiency. The tax is due to the current high-cost contribution of H 2 generation to the minimum selling price of MeOH. In the absence of a tax, NTCs for H 2 production offer a PED elec that is comparable to the fossil-based commercial process, but this approach will probably only be viable in the mid- to long-term. In the near- to mid-term, the key enablers are renewable and affordable electricity for H 2 generation and CO 2 capture with an appropriate carbon tax, and for all scenarios a selective, solar-derived, scalable and robust RWGS or SOEC process for CO, as we transition to a carbon-neutral society. References . 1. Henze, V. Energy storage is a $620 billion investment opportunity to 2040. BloombergNEF. https://about.bnef.com/blog/energy-storage-620-billion-investment-opportunity-2040/ (2018). 2. Dias, V., Pochet, M., Contino, F. & Jeanmart, H. Energy and economic costs of chemical storage. Front. Mech. Eng. https://doi.org/10.3389/fmech.2020.00021 (2020). 3. Kaiser, P., Unde, R. B., Kern, C. & Jess, A. Production of liquid hydrocarbons with CO 2 as carbon source based on reverse water-gas shift and Fischer-Tropsch synthesis. Chem. Ing. Tech. 85 , 489–499 (2013). CAS ? Google Scholar ? 4. Graver, B., Rutherford, D. & Zheng, S. CO 2 Emissions from Commercial Aviation: 2013, 2018, and 2019 (International Council on Clean Transportation, 2020). 5. Reducing emissions from the shipping sector. European Commission www.ec.europa.eu/clima/policies/transport/shipping_en (2020). 6. Service, R. F. Can the world make the chemicals it needs without oil? Science (19 September 2019). 7. Global CO 2 emissions in 2019. International Energy Agency https://www.iea.org/articles/global-co2-emissions-in-2019 (2020). 8. IRENA and Methanol Institute. Innovation Outlook: Renewable Methanol (International Renewable Energy Agency, 2021). 9. Tountas, A. A. et al. Towards solar methanol: past, present, and future. Adv. Sci. 6 , 1801903 (2019). Google Scholar ? 10. Sigwadi, R., Mokrani, T., Dhlamini, S. & Msomi, P. F. Nafion? reinforced with polyacrylonitrile/ZrO 2 nanofibers for direct methanol fuel cell application. J. Appl. Polym. Sci. 138 , 49978 (2021). CAS ? Google Scholar ? 11. Hyatt, K. California to ban new gas, diesel vehicle sales by 2035. Roadshow by CNET https://www.cnet.com/roadshow/news/california-gas-diesel-car-truck-sales-ban-2035-newsom/#ftag=CAD590a51e (2020). 12. Cipriani, G. et al. Perspective on hydrogen energy carrier and its automotive applications. Int. J. Hydrog. Energy 39 , 8482–8494 (2014). CAS ? Google Scholar ? 13. Olah, G. A., Goeppert, A. & Prakash, G. K. S. Beyond Oil and Gas: The Methanol Economy 2nd edn (Wiley, 2009) 14. Ouyang, L., Chen, K., Jiang, J., Yang, X. S. & Zhu, M. Hydrogen storage in light-metal based systems: a review. J. Alloys Compd 829 , 154597 (2020). CAS ? Google Scholar ? 15. New powerpaste for hydrogen storage. Renewable Energy Magazine https://www.renewableenergymagazine.com/hydrogen/new-powerpaste-for-hydrogen-storage-20210204 (2021). 16. Bongartz, D., Burre, J. & Mitsos, A. Production of oxymethylene dimethyl ethers from hydrogen and carbon dioxide—part I: modeling and analysis for OME 1 . Ind. Eng. Chem. Res. 58 , 4881–4889 (2019). CAS ? Google Scholar ? 17. Sá, S., Silva, H., Brand?o, L., Sousa, J. M. & Mendes, A. Catalysts for methanol steam reforming—a review. Appl. Catal. B 99 , 43–57 (2010). Google Scholar ? 18. Herron, J. A., Kim, J., Upadhye, A. A., Huber, G. W. & Maravelias, C. T. A general framework for the assessment of solar fuel technologies. Energy Environ. Sci. 8 , 126–157 (2015). CAS ? Google Scholar ? 19. Ramsden, T., Steward, D. & Zuboy, J. Analyzing the Levelized Cost of Centralized and Distributed Hydrogen Production Using the H2A Production Model, Version 2 (National Renewable Energy Laboratory, 2009). 20. Ainscough, C., Peterson, D. & Miller, E. Hydrogen Production Cost From PEM Electrolysis (US Department of Energy, 2014). 21. El-Emam, R. S. & ?zcan, H. Comprehensive review on the techno-economics of sustainable large-scale clean hydrogen production. J. Clean. Prod. 220 , 593–609 (2019). CAS ? Google Scholar ? 22. Herring, S. J. et al. Hydrogen Production Using Nuclear Energy NP-T-4.2 (International Atomic Energy Agency, 2013). 23. Zheng, Y. et al. A review of high temperature co-electrolysis of H 2 O and CO 2 to produce sustainable fuels using solid oxide electrolysis cells (SOECs): advanced materials and technology. Chem. Soc. Rev. 46 , 1427–1463 (2017). CAS ? PubMed ? Google Scholar ? 24. Graves, C., Ebbesen, S. D., Mogensen, M. & Lackner, K. S. Sustainable hydrocarbon fuels by recycling CO 2 and H 2 O with renewable or nuclear energy. Renew. Sustain. Energy Rev. 15 , 1–23 (2011). CAS ? Google Scholar ? 25. Revankar, S. T. in Storage and Hybridization of Nuclear Energy: Techno-economic Integration of Renewable and Nuclear Energy (eds Bindra, H. & Revankar, S. T.) Ch. 4 (Academic, 2018). 26. Direct air capture as an enabler of ultra-low carbon fuels. Carbon Engineering https://carbonengineering.com/wp-content/uploads/2019/11/DAC-as-an-enabler-of-ultra-low-cost-carbon-fuels.pdf (2013). 27. Keith, D. W., Holmes, G., St. Angelo, D. & Heidel, K. A process for capturing CO 2 from the atmosphere. Joule 2 , 1573–1594 (2018). CAS ? Google Scholar ? 28. Welch, A. J., Dunn, E., Duchene, J. S. & Atwater, H. A. Bicarbonate or carbonate processes for coupling carbon dioxide capture and electrochemical conversion. ACS Energy Lett. 5 , 940–945 (2020). CAS ? Google Scholar ? 29. Folger, P. Carbon Capture: A Technology Assessment (Congressional Research Service, 2013). 30. Fasihi, M., Efimova, O. & Breyer, C. Techno-economic assessment of CO 2 direct air capture plants. J. Clean. Prod. 224 , 957–980 (2019). CAS ? Google Scholar ? 31. Gebald, C., Wurzbacher, J. A., Tingaut, P., Zimmermann, T. & Steinfeld, A. Amine-based nanofibrillated cellulose as adsorbent for CO 2 capture from air. Environ. Sci. Technol. 45 , 9101–9108 (2011). CAS ? PubMed ? Google Scholar ? 32. Direct air capture to help reverse climate change. Climeworks www.climeworks.com/co2-removal (2020). 33. Realmonte, G. et al. An inter-model assessment of the role of direct air capture in deep mitigation pathways. Nat. Commun. 10 , 3277 (2019). CAS ? PubMed ? PubMed Central ? Google Scholar ? 34. Fujikawa, S., Selyanchyn, R. & Kunitake, T. A new strategy for membrane-based direct air capture. Polym. J. 53 , 111–119 (2021). CAS ? Google Scholar ? 35. Wenzel, M., Rihko-Struckmann, L. & Sundmacher, K. Thermodynamic analysis and optimization of RWGS processes for solar syngas production from CO 2 . AIChE J. 63 , 15–22 (2017). CAS ? Google Scholar ? 36. González-Casta?o, M., Dorneanu, B. & Arellano-García, H. The reverse water gas shift reaction: a process systems engineering perspective. React. Chem. Eng. 6 , 954–976 (2021). Google Scholar ? 37. Daza, Y. A. & Kuhn, J. N. CO 2 conversion by reverse water gas shift catalysis: comparison of catalysts, mechanisms and their consequences for CO 2 conversion to liquid fuels. RSC Adv. 6 , 49675–49691 (2016). CAS ? Google Scholar ? 38. Porosoff, M. D., Yan, B. & Chen, J. G. Catalytic reduction of CO 2 by H 2 for synthesis of CO, methanol and hydrocarbons: challenges and opportunities. Energy Environ. Sci. 9 , 62–73 (2016). CAS ? Google Scholar ? 39. Vidal Vázquez, F. et al. Catalyst screening and kinetic modeling for CO production by high pressure and temperature reverse water gas shift for Fischer-Tropsch applications. Ind. Eng. Chem. Res. 56 , 13262–13272 (2017). Google Scholar ? 40. Dong, Y. et al. Shining light on CO 2 : from materials discovery to photocatalyst, photoreactor and process engineering. Chem. Soc. Rev. 49 , 5648–5663 (2020). CAS ? Google Scholar ? 41. De Falco, M., Iaquaniello, G. & Centi, G. (eds) CO 2 : A Valuable Source of Carbon Vol. 137 (Springer, 2013). 42. Elsernagawy, O. Y. H. et al. Thermo-economic analysis of reverse water-gas shift process with different temperatures for green methanol production as a hydrogen carrier. J. CO 2 Util. 41 , 101280 (2020). 43. Küngas, R. et al. eCOs - a commercial CO 2 electrolysis system developed by Haldor Topsoe. ECS Trans. 78 , 2879–2884 (2017). Google Scholar ? 44. Bushuyev, O. S. et al. What should we make with CO 2 and how can we make it? Joule 2 , 825–832 (2018). CAS ? Google Scholar ? 45. Natesakhawat, S. et al. Adsorption and deactivation characteristics of Cu/ZnO-based catalysts for methanol synthesis from carbon dioxide. Top. Catal. 56 , 1752–1763 (2013). CAS ? Google Scholar ? 46. Pra?nikar, A., Pavli?i?, A., Ruiz-Zepeda, F., Kova?, J. & Likozar, B. Mechanisms of copper-based catalyst deactivation during CO 2 reduction to methanol. Ind. Eng. Chem. Res. 58 , 13021–13029 (2019). Google Scholar ? 47. Etim, U. J., Song, Y. & Zhong, Z. Improving the Cu/ZnO-based catalysts for carbon dioxide hydrogenation to methanol, and the use of methanol as a renewable energy storage media. Front. Energy Res. https://doi.org/10.3389/fenrg.2020.545431 (2020). 48. Fichtl, M. B. et al. Kinetics of deactivation on Cu/ZnO/Al 2 O 3 methanol synthesis catalysts. Appl. Catal. A 502 , 262–270 (2015). CAS ? Google Scholar ? 49. Kung, H. H. Deactivation of methanol synthesis catalysts - a review. Catal. Today 11 , 443–453 (1992). CAS ? Google Scholar ? 50. Tountas, A. A., Ozin, G. A. & Sain, M. M. Continuous reactor for renewable methanol. Green. Chem. 23 , 340–353 (2021). CAS ? Google Scholar ? 51. Dieterich, V., Buttler, A., Hanel, A., Spliethoff, H. & Fendt, S. Power-to-liquid via synthesis of methanol, DME or Fischer–Tropsch-fuels: a review. Energy Environ. Sci. 13 , 3207–3252 (2020). CAS ? Google Scholar ? 52. Sarp, S., Hernandez, S. G., Chen, C. & Sheehan, S. W. Alcohol production from carbon dioxide: methanol as a fuel and chemical feedstock. Joule 5 , 59–76 (2021). CAS ? Google Scholar ? 53. Bos, M. J. & Brilman, D. W. F. A novel condensation reactor for efficient CO 2 to methanol conversion for storage of renewable electric energy. Chem. Eng. J. 278 , 527–532 (2015). CAS ? Google Scholar ? 54. Stechel, E. B. & Miller, J. E. Re-energizing CO 2 to fuels with the sun: issues of efficiency, scale, and economics. J. CO 2 Util. 1 , 28–36 (2013). 55. Lee, B. et al. Renewable methanol synthesis from renewable H 2 and captured CO 2 : how can power-to-liquid technology be economically feasible? Appl. Energy 279 , 115827 (2020). CAS ? Google Scholar ? 56. Juneau, M. et al. Assessing the viability of K-Mo 2 C for reverse water-gas shift scale-up: molecular to laboratory to pilot scale. Energy Environ. Sci. 13 , 2524–2539 (2020). CAS ? Google Scholar ? 57. Joo, O.-S. et al. Carbon dioxide hydrogenation to form methanol via a reverse-water-gas-shift reaction (the CAMERE process). Ind. Eng. Chem. Res. 38 , 1808–1812 (1999). CAS ? Google Scholar ? 58. Dimitriou, I. et al. Carbon dioxide utilisation for production of transport fuels: process and economic analysis. Energy Environ. Sci. 8 , 1775–1789 (2015). CAS ? Google Scholar ? 59. Zubrin, R. M., Muscatello, A. C. & Berggren, M. Integrated Mars in situ propellant production system. J. Aerosp. Eng. 26 , 43–56 (2013). Google Scholar ? 60. Yang, Y., Mims, C. A., Mei, D. H., Peden, C. H. F. & Campbell, C. T. Mechanistic studies of methanol synthesis over Cu from CO/CO 2 /H 2 /H 2 O mixtures: the source of C in methanol and the role of water. J. Catal. 298 , 10–17 (2013). CAS ? Google Scholar ? 61. Marlin, D. S., Sarron, E. & Sigurbj?rnsson, ?. Process advantages of direct CO 2 to methanol synthesis. Front. Chem. https://doi.org/10.3389/fchem.2018.00446 (2018). 62. Hafeez, S., Manos, G., Al-Salem, S. M., Aristodemou, E. & Constantinou, A. Liquid fuel synthesis in microreactors. React. Chem. Eng. 3 , 414–432 (2018). CAS ? Google Scholar ? 63. Chan, T. Renewable methanol webinar: a net carbon-neutral fuel. Methanol Institute (5 August 2020). 64. Vanden Bussche, K. M. & Froment, G. F. A steady-state kinetic model for methanol synthesis and the water gas shift reaction on a commercial Cu/ZnO/Al 2 O 3 catalyst. J. Catal. 161 , 1–10 (1996). CAS ? Google Scholar ? 65. Slotboom, Y. et al. Critical assessment of steady-state kinetic models for the synthesis of methanol over an industrial Cu/ZnO/Al 2 O 3 catalyst. Chem. Eng. J. 389 , 124181 (2020). CAS ? Google Scholar ? 66. Bozzano, G. & Manenti, F. Efficient methanol synthesis: perspectives, technologies and optimization strategies. Prog. Energy Combust. Sci. 56 , 71–105 (2016). Google Scholar ? 67. Bertau, M. et al. (eds), Methanol: The Basic Chemical and Energy Feedstock of the Future (Springer, 2014). 68. Bukhtiyarova, M., Lunkenbein, T., K?hler, K. & Schl?gl, R. Methanol synthesis from industrial ? CO 2 sources: a contribution to chemical energy conversion. Catal. Lett. 147 , 416–427 (2017). CAS ? Google Scholar ? 69. Rezaie, N., Jahanmiri, A., Moghtaderi, B. & Rahimpour, M. R. A comparison of homogeneous and heterogeneous dynamic models for industrial methanol reactors in the presence of catalyst deactivation. Chem. Eng. Process. 44 , 911–921 (2005). CAS ? Google Scholar ? 70. Prieto, G., Meeldijk, J. D., De Jong, K. P. & De Jongh, P. E. Interplay between pore size and nanoparticle spatial distribution: consequences for the stability of CuZn/SiO 2 methanol synthesis catalysts. J. Catal. 303 , 31–40 (2013). CAS ? Google Scholar ? 71. Riaz, A., Zahedi, G. & Kleme?, J. J. A review of cleaner production methods for the manufacture of methanol. J. Clean. Prod. 57 , 19–37 (2013). CAS ? Google Scholar ? 72. Klier, K., Chatikavanu, R., Herman, G. & Simmons, G. W. Catalytic synthesis of methanol from CO/H 2 : IV. The effects of carbon dioxide. J. Catal. 74 , 343–360 (1982). CAS ? Google Scholar ? 73. Rasmussen, D. B. et al. The energies of formation and mobilities of Cu surface species on Cu and ZnO in methanol and water gas shift atmospheres studied by DFT. J. Catal. 293 , 205–214 (2012). CAS ? Google Scholar ? 74. Breeze, P. in Power System Energy Storage Technologies Ch. 5 (Academic, 2018); https://doi.org/10.1016/B978-0-12-812902-9.00005-5 75. Miller, J. R. Capacitors for Power Grid Storage (US Department of Energy, 2010); https://www.energy.gov/sites/prod/files/piprod/documents/Session_D_Miller_rev.pdf 76. Fact Sheet: Frequency Regulation and Flywheels. Beacon Power https://web.archive.org/web/20100331042630/http://www.beaconpower.com/files/Flywheel_FR-Fact-Sheet.pdf (31 March 2010). 77. Esparcia, E. A., Castro, M. T., Buendia, R. E. & Ocon, J. D. Long-discharge flywheel versus battery energy storage for microgrids: a techno-economic comparison. Chem. Eng. Trans. 76 , 949–954 (2019). Google Scholar ? 78. Highly efficient electromechanical energy storage. American Maglev Technology http://american-maglev.com/fess (accessed 31 October 2021). 79. Jacob, R., Saman, W. & Bruno, F. Capital cost expenditure of high temperature latent and sensible thermal energy storage systems. AIP Conf. Proc. 1850 , 080012 (2017). Google Scholar ? 80. Zablocki, A. Fact Sheet: Energy Storage (2019). Environmental and Energy Study Institute https://www.eesi.org/papers/view/energy-storage-2019 (2019). 81. Park, S. W., Joo, O. S., Jung, K. D., Kim, H. & Han, S. H. Development of ZnO/Al 2 O 3 catalyst for reverse-water-gas-shift reaction of CAMERE (carbon dioxide hydrogenation to form methanol via a reverse-water-gas-shift reaction) process. Appl. Catal. A 211 , 81–90 (2001). CAS ? Google Scholar ? Download references Acknowledgements . Thank you to X. Peng and C. T. Maravelias for the referenced TEA analysis. Thank you to K. Raina for proofreading the manuscript. We thank J. Fryer for the art concept for the graphical abstract and Fig. 2a . All authors thank J. Tjong of Ford Motor Canada for financial support. G.A.O. acknowledges the financial support of the Ontario Ministry of Research and Innovation (MRI), the Ministry of Economic Development, Employment and Infrastructure (MEDI), the Ministry of the Environment and Climate Change’s (MOECC) Best in Science (BIS) Award, Ontario Centre of Excellence Solutions 2030 Challenge Fund, Ministry of Research Innovation and Science (MRIS) Low Carbon Innovation Fund (LCIF), Imperial Oil, the University of Toronto’s Connaught Innovation Fund (CIF), Connaught Global Challenge (CGC) Fund and the Natural Sciences and Engineering Research Council of Canada (NSERC). Author information . Affiliations . Department of Chemical Engineering and Applied Chemistry, University of Toronto, Toronto, Ontario, Canada Athanasios A. Tountas?&?Mohini M. Sain Department of Chemistry, University of Toronto, Toronto, Ontario, Canada Geoffrey A. Ozin Department of Mechanical and Industrial Engineering, University of Toronto, Toronto, Ontario, Canada Mohini M. Sain Authors Athanasios A. Tountas View author publications You can also search for this author in PubMed ? Google Scholar Geoffrey A. Ozin View author publications You can also search for this author in PubMed ? Google Scholar Mohini M. Sain View author publications You can also search for this author in PubMed ? Google Scholar Contributions . A.A.T. conceived the analysis and wrote the Perspective. G.A.O. and M.M.S. provided critical guidance and advice. Corresponding author . Correspondence to Geoffrey A. Ozin . Ethics declarations . Competing interests . The authors declare no competing interests. Additional information . Peer review information Nature Catalysis thanks the anonymous reviewers for their contribution to the peer review of this work. Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. Rights and permissions . Reprints and Permissions About this article . Cite this article . Tountas, A.A., Ozin, G.A. & Sain, M.M. Solar methanol energy storage. Nat Catal 4, 934–942 (2021). https://doi.org/10.1038/s41929-021-00696-w Download citation Received : 30 December 2020 Accepted : 04 October 2021 Published : 18 November 2021 Issue Date : November 2021 DOI : https://doi.org/10.1038/s41929-021-00696-w Share this article . Anyone you share the following link with will be able to read this content: Get shareable link Sorry, a shareable link is not currently available for this article. Copy to clipboard Provided by the Springer Nature SharedIt content-sharing initiative .
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