Two‐electron water oxidation reaction (2e‐WOR) to produce hydrogen peroxide (H 2 O 2 ) is an attractive anode reaction with several merits. It can be paired with several large‐scale cathode reactions that produce valuable chemical substances in an electrochemical cell. However, high‐performing and reliable 2e‐WOR anodic catalysts are yet to be fully developed. In this work, a rationally designed, inexpensive, robust, and selective graphite catalyst electrode is presented, made by following the key principle mechanisms of 2e‐WOR. First, an aerophilic graphite‐based electrode is created to leverage the challenges posed by the four‐electron WOR, where the generated O 2 from this reaction is kept onto the electrode surface to shift the O intermediates binding on graphite in the direction of improved H 2 O 2 generation. An initial improvement in H 2 O 2 selectivity of seven fold is observed, albeit with no improved H 2 O 2 generation rates. The stunted H 2 O 2 generation is ascribed to poor activity from pristine graphite, courtesy of less active sites and low intrinsic O 2 binding in the electrolyte environment. Second, to improve and balance graphite's activity and selectivity, the structure of graphite is altered via different elemental doping (with N, S, B, and P atoms), a method that allows the retention of the O 2 on the graphite surface. The super‐aerophilic B‐doped graphite catalyst (optimum) reaches a maximum Faraday efficiency (FE) of 60.6 ± 2.6% with a production rate of 26.7 ± 0.6 µmol min −1 cm −2 (85.9 ± 2.2 mA cm −2 partial current density) and excellent stability of over 120 h. In tandem, cathodic H 2 co‐production is demonstrated with an FE of above 90%. This approach demonstrates a rational approach to designing inexpensive and robust 2e‐WOR anode catalysts for H 2 O 2 and the possibility of its use in chemical co‐production at the cathode.

The world's transition from a fossil-fuel-driven society to a future net-zero or negative carbon dioxide emission society will require a significant scale-up of Power-to-X technologies to capture and convert CO2 to low carbon intensity fuels and chemicals. The deployment of Power-to-X technologies at gigawatt scales necessary to impact CO2 emissions and replace existing fossil-fuel-dependent processes will require vast quantities of raw materials and minerals. Many of the materials required in Power-to-X systems, such as rare earth metal yttrium and iridium, differ from those used to construct and operate petroleum-hydrocarbon-based processes for the last 100 years. Thus, electrolyzer manufacturers and mineral producers face significant challenges in matching supply to the growing demand. In this Perspective, we identify critical materials needed for Power-to-X electrolyzers and analyze the impacts and risks of these materials' existing global supply chains. We then provide an overview of methodologies for Environmental Life Cycle Assessment (LCA) and Social Life Cycle Assessment (SLCA) that we encourage scientific communities to adopt early in the research process to evaluate the multidimensional socio-environmental impacts throughout a product's life cycle, from raw material extraction and processing to manufacturing, use, and end-of-life disposal. We advocate that life cycle thinking is crucial for the informed, just and ethical development of disruptive technologies and systems such as Power-to-X technologies.

The path to practical production of targeted chemicals and fuels application via carbon dioxide reduction reactions (CO2RRs) remains a significant challenge mainly due to low CO2 solubility. Aiming to tackle this key issue, herein, we used the CuSbOx cathode-catalyzed reduction of CO2 to CO as a model system to quantitatively depict CO2 demand-supply and performance relationships. We propose a cathode/electrolyte interface model consisting of a porous catalyst layer, and we combined the experimental and computational COMSOL Multiphysics finite-element studies to quantitatively unveil CO2 demand-supply relationships and determine the maximum CO2 supply capacity in both stationary H cell and gas diffusion electrode (GDE) flow cell. This work exemplifies that experimentally measured catalytic performance may not accurately reflect the maximum capacity/intrinsic electrocatalytic activity of electrocatalysts and reveals that CO2 supply capacity in the GDE flow cell can be dramatically affected by the thickness of the liquid layer between the hydrophobic gas diffusion layer and the catalyst layer.

Perovskite oxides have emerged as promising photocatalysts for CO 2 reduction to valuable chemicals and fuels. However, conventional perovskite oxide photocatalysts often suffer from inefficient charge separation and bulk charge recombination, negatively impacting overall photoactivity. In this work, we present a novel immobilized perovskite oxide -based photocatalyst sheet featuring an indirect Z -scheme heterostructure composed of Culoaded Al -doped SrTiO 3 (Cu-ASTO) and CoO x -loaded WO 3 (CoO x -WO 3 ) with an ultrathin (20 nm) gold interlayer serving as a conductive bridge. We tested this photocatalyst sheet in a sealed reactor containing a CO 2 - saturated aqueous solution of 0.1 M NaHCO 3 and a side window to allow irradiation. Under irradiation with a 300 W Xe lamp, the Cu-ASTO/Au/CoO x -WO 3 immobilized photocatalyst sheet produced methane (CH 4 ) at a rate of 2.676 pmol cm -2 h -1 and methanol (CH 3 OH) at 0.517 pmol cm -2 h -1 . We attribute the superior activity of this catalyst to the all -solid-state indirect Z -scheme heterostructure that greatly extends the lifespan of photoinduced charge carriers and enhances the CO 2 photoconversion reaction. In experiments conducted outside, we demonstrated the immobilized photocatalyst 's performance under natural sunlight, producing CH 4 at 0.307 pmol cm -2 h -1 and CH 3 OH at 0.069 pmol cm -2 h -1 . This work provides design ideas for developing robust immobilized photocatalyst systems for the scalable operation of the CO 2 photoreduction process and broadening the scope of applications for perovskite heterostructure photocatalysts.

Perovskite oxides have emerged as promising photocatalysts for CO2 reduction to valuable chemicals and fuels. However, conventional perovskite oxide photocatalysts often suffer from inefficient charge separation and bulk charge recombination, negatively impacting overall photoactivity. In this work, we present a novel immobilized perovskite oxide-based photocatalyst sheet featuring an indirect Z-scheme heterostructure composed of Cu-loaded Al-doped SrTiO3 (Cu-ASTO) and CoOx-loaded WO3 (CoOx-WO3) with an ultrathin (20 nm) gold interlayer serving as a conductive bridge. We tested this photocatalyst sheet in a sealed reactor containing a CO2-saturated aqueous solution of 0.1 M NaHCO3 and a side window to allow irradiation. Under irradiation with a 300 W Xe lamp, the Cu-ASTO/Au/CoOx-WO3 immobilized photocatalyst sheet produced methane (CH4) at a rate of 2.676 µmol cm-2 h−1 and methanol (CH3OH) at 0.517 µmol cm-2 h−1. We attribute the superior activity of this catalyst to the all-solid-state indirect Z-scheme heterostructure that greatly extends the lifespan of photoinduced charge carriers and enhances the CO2 photoconversion reaction. In experiments conducted outside, we demonstrated the immobilized photocatalyst's performance under natural sunlight, producing CH4 at 0.307 µmol cm-2 h−1 and CH3OH at 0.069 µmol cm-2 h−1. This work provides design ideas for developing robust immobilized photocatalyst systems for the scalable operation of the CO2 photoreduction process and broadening the scope of applications for perovskite heterostructure photocatalysts.

Hydrogen peroxide (H2O2) is a crucial chemical applied in various industry sectors. However, the current industrial anthraquinone process for H2O2 synthesis is carbon-intensive. With sunlight and renewable electricity as energy inputs, photocatalysis and electrocatalysis have great potential for green H2O2 production from oxygen (O2) and water (H2O). Herein, we review the advances in pairing two-electron O2 reduction and two-electron H2O oxidation reactions for dual-pathway H2O2 synthesis. The basic principles, paired redox reactions, and catalytic device configurations are introduced initially. Aligning with the energy input, the latest photocatalysts, electrocatalysts, and photo-electrocatalysts for dual-pathway H2O2 production are discussed afterward. Finally, we outlook the research opportunities in the future. This minireview aims to provide insights and guidelines for the broad community who are interested in catalyst design and innovative technology for on-site H2O2 synthesis.

Electrolyte flooding in porous catalyst layers on gas diffusion electrodes (GDE) limits the stability and high-current performance of CO2 and CO electrolyzers. Here, we demonstrate the in situ electroreduction of graphene oxide (GO) to reduced graphene oxide (r-GO) within a silver catalyst layer on a carbon GDE. The r-GO introduces hydrophobicity regions in the catalyst layer that help mitigate electrolyte flooding during high current density CO2 electrolysis to CO. The flooding-resistant r-GO/Ag-coated GDE achieves a sustained Faradaic efficiency of CO at 94% for more than 8 h, compared to a rapid drop from 95% to 66% in an Ag-coated GDE without r-GO at 100 mAcm(-2). We found that GO enhances the electrochemically active surface area of the catalyst layer during CO2 electrolysis tests because the incorporation of GO increases the roughness of the catalyst layer. The in situ method of electrochemically reducing GO to r-GO provides a low-cost, practical approach that can be applied during standard spray-deposition procedures to develop flooding-resistant GDEs.

Titanate perovskite (ATiO(3)) semiconductors show prospects of being active photocatalysts in the conversion of CO2 to chemical fuels such as methanol (CH3OH) in the aqueous phase. Some of the challenges in using ATiO(3) are limited light-harvesting capability, rapid bulk charge recombination, and the low density of catalytic sites participating in CO2 reduction. To address these challenges, Ga-doped NiTiO3 (GNTO) photocatalysts in which Ga ions substitute for Ti ions in the crystal lattice to form electron trap states and oxygen vacancies have been synthesized in this work. The synthesized GNTO was then loaded with Ru nanoparticles to accelerate charge separation and enable excellent CO2 photoreduction activity under visible light. CO2 photoreduction was conducted in a batch photoreactor charged with a 0.1 M NaHCO3 aqueous solution at room temperature and a 3.5 bar pressure using a 1.0 wt % Ru-GNTO photocatalyst to yield methanol at a rate of 84.45 mu mol g(-1) h(-1). A small amount of methane was produced as a side product at 21.35 mu mol g(-1) h(-1), which is also a fuel molecule. We attribute this high catalytic activity toward CO2 photoreduction to a synergistic combination of our novel heterostructured 1.0 wt % Ru-GNTO photocatalyst and the implementation of a pressurized photoreactor. This work demonstrates an effective strategy for metal doping with active nanospecies functionality to improve the performance of ATiO(3) photocatalysts in valorizing CO2 to solar fuels.

One of the many possible ways to capture carbon dioxide (CO2) is through electrochemical means. This is an emerging approach with various merits. It is energy efficient, utilizes renewable energy, operates under ambient conditions, provides ease for control of reaction rates, and is scalable. Additionally, it can be integrated as a plug-and-play module at various scales, including large industrial sources or at small scale, e.g., on vehicles, and can easily combine CO2 capture, storage, and utilization into value-added chemicals. Various "proof-of-concept" electrochemical CO2 capture approaches have been demonstrated in the recent past. These are made possible with electro-active materials that capture, separate, and concentrate CO2 in the form of electrodes, electrolytes, and membranes in devices. Herein, these materials and their working mechanisms are identified and reviewed in various electrochemical CO2 capture devices where they are utilized. Also, the current challenges and future research directions with the identified electrodes, electrolytes, and membranes are summarized to give a rational understanding and guidance for selecting and designing materials for use in electrochemical CO2 capture devices.

Electrochemical reduction of CO 2 presents an attractive way to store renewable energy in chemical bonds in a potentially carbon-neutral way. However, the available electrolyzers suffer from intrinsic problems, like flooding and salt accumulation, that must be overcome to industrialize the technology. To mitigate flooding and salt precipitation issues, researchers have used super-hydrophobic electrodes based on either expanded polytetrafluoroethylene (ePTFE) gas-diffusion layers (GDL’s), or carbon-based GDL’s with added PTFE. While the PTFE backbone is highly resistant to flooding, the non-conductive nature of PTFE means that without additional current collection the catalyst layer itself is responsible for electron-dispersion, which penalizes system efficiency and stability. In this work, we present operando results that illustrate that the current distribution and electrical potential distribution is far from a uniform distribution in thin catalyst layers (~50 nm) deposited onto ePTFE GDL’s. We then compare the effects of thicker catalyst layers (~500 nm) and a newly developed non-invasive current collector (NICC). The NICC can maintain more uniform current distributions with 10-fold thinner catalyst layers while improving stability towards ethylene (≥ 30%) by approximately two-fold.

The electrochemical CO2 reduction reaction (CO2RR), driven by renewable energy, provides a potential carbon-neutral avenue to convert CO2 into valuable fuels and feedstocks. Conversion of CO2 into formic acid/formate is considered one of the economical and feasible methods, owing to their high energy densities, and ease of distribution and storage. The separation of formic acid/formate from the reaction mixtures accounts for the majority of the overall CO2RR process cost, while the increment of product concentration can lead to the reduction of separation cost, remarkably. In this paper, we give an overview of recent strategies for highly concentrated formic acid/formate products in CO2RR. CO2RR is a complex process with several different products, as it has different intermediates and reaction pathways. Therefore, this review focuses on recent study strategies that can enhance targeted formic acid/formate yield, such as the all-solid-state reactor design to deliver a high concentration of products during the reduction of CO2 in the electrolyzer. Firstly, some novel electrolyzers are introduced as an engineering strategy to improve the concentration of the formic acid/formate and reduce the cost of downstream separations. Also, the design of planar and gas diffusion electrodes (GDEs) with the potential to deliver high-concentration formic acid/formate in CO2RR is summarized. Finally, the existing technological challenges are highlighted, and further research recommendations to achieve high-concentration products in CO2RR. This review can provide some inspiration for future research to further improve the product concentration and economic benefits of CO2RR.

The blast furnace (BF) ironmaking is an energy-intensive process and the largest source of CO2 emissions in an integrated steel mill. We evaluated the potential energy, fresh coke savings and associated reductions in CO2 emissions for a BF operation if some CO2 in the BF gases were converted to CO using an electrochemical CO2 conversion process and that CO was recycled to the BF. As an added benefit, the electrochemical process produces H2 and O2, which helps iron ores reduction and oxygen enrichment. This paper presents a mathematical model of BF that integrates CO2 capture, CO2 electrolysis, and gas injection. Our results show that integrating a CO2 to CO electrolysis process in a traditional ironmaking plant could reduce coke consumption from 386 kg/ tHM to 260 kg/tHM at a 9% oxygen enrichment rate. A maximum 40% reduction in the CO2 emissions per ton of hot metal can be reached. However, the total energy consumption of the process increases when the CO2 electrolysis unit is included. Consequently, realising these potential CO2 savings requires the availability of zerocarbon electricity from renewable sources. Improvements in the selectivity and efficiency of the CO2 electrolysis in the future may enhance the overall economics and efficiency of this process.

To explore the effects of solvent-ionomer interactions in catalyst inks on the structure and performance of Cu catalyst layers (CLs) for CO2 electrolysis, we used a "like for like" rationale to select acetone and methanol as dispersion solvents with a distinct affinity for the ionomer backbone or sulfonated ionic heads, respectively, of the perfluorinated sulfonic acid (PFSA) ionomer Aquivion. First, we characterized the morphology and wettability of Aquivion films drop-cast from acetone- and methanol-based inks on flat Cu foils and glassy carbons. On a flat surface, the ionomer films cast from the Aquivion and acetone mixture were more continuous and hydrophobic than films cast from methanol-based inks. Our study's second stage compared the performance of Cu nanoparticle CLs prepared with acetone and methanol on gas diffusion electrodes (GDEs) in a flow cell electrolyzer. The effects of the ionomer-solvent interaction led to a more uniform and flooding-tolerant GDE when acetone was the dispersion solvent (acetone-CL) than when we used methanol (methanol-CL). As a result, acetone-CL yielded a higher selectivity for CO2 electrolysis to C2+ products at high current density, up to 25% greater than methanol-CL at 500 mA cm-2. Ethylene was the primary product for both CLs, with a Faradaic efficiency for ethylene of 47.4 ± 4.0% on the acetone-CL and that of 37.6 ± 5.5% on the methanol-CL at a current density of 300 mA cm-2. We attribute the enhanced C2+ selectivity of the acetone-CL to this electrode's better resistance to electrolyte flooding, with zero seepage observed at tested current densities. Our findings reveal the critical role of solvent-ionomer interaction in determining the film structure and hydrophobicity, providing new insights into the CL design for enhanced multicarbon production in high current densities in CO2 electrolysis processes.

Electrocatalytic carbon dioxide (CO2) reduction reaction (CO2RR) is a promising process to mitigate the environmental issues caused by CO2, as well as to produce valuable multicarbon (C2+) products. Sig-nificant progresses have been made to explore highly efficient Cu-based electrocatalysts for CO2RR in recent years. Adding organic molecules into electrocatalytic systems can tune the CO2 interaction with the electrocatalysts for CO2RR, therefore, the final C2+ products, which are not solely achieved by inor-ganic modification. In this review, we will summarize the recent progress of the organic molecules participation in CO2 electroreduction to C2+ products on Cu-based electrocatalysts. The applied organic molecules are reviewed based on the heteroatoms (N and S), with the emphasis on their roles in activity and selectivity toward C2+ products. A perspective on the application of organic molecules for efficient and selective CO2RR has been provided.(c) 2022 Elsevier Ltd. All rights reserved.

Understanding the relationship between gas diffusion electrode (GDE) structures and the performance of electrochemical CO2 reduction reaction (CO2RR) is crucial to developing industrial-scale technologies to convert CO2 to valuable products. We studied how the microporous layer (MPL) on GDE's coated with silver nanoparticle catalysts affects the electrochemical CO2 conversion to CO in a flow cell electrolyser. We demonstrate a convenient method to measure the rate of catholyte seepage through a GDE during CO2RR experiments and used this method to show how the MPL thickness affects flooding of the GDE. We found the GDE with the thickest MPL (39BB) had the best selectivity for CO and stability at current densities above 100 mA cm−2 as the thick MPL minimized flooding. However, at low current densities the 39BB electrode achieved a lower CO selectivity than the GDE with thinner MPL. These results suggest opportunities to improve CO2 electrolyser performances at high current by optimisation of the MPL structure and wettability.

Achieving operational stability at high current densities remains a challenge in CO2 electrolyzers due to flooding of the gas diffusion layer (GDL) that supports the electrocatalyst. We mitigated electrode flooding at high current densities using a vacuum-assisted infiltration method to embed 200-400 nm-sized polytetrafluoroethylene (PTFE) particles at the interface of the microporous layer (MPL) and carbon cloth in a commercial GDL. In CO2 electrolysis to CO over a silver nanoparticle catalyst on the GDL, the PTFE-embedded GDL not only just exhibited less than 10% of the electrolyte seepage rates observed in untreated GDLs at a current density of 300 mA center dot cm(-2) but also expanded the electrochemical active area across the testing conditions. The PTFE-embedded GDL also maintained a Faradaic efficiency for CO2 electrolysis to CO above 80% for more than 100 h at 100 mA center dot cm(-2), which was a 50-fold improvement in the stable operation time of the electrolyzer.

Regulating the rational wettability on gas-diffusion electrodes (GDEs) plays a pivotal role to improve the effi-iency of CO2RR via fine-tuning the reaction zone and boosting the formation of triple-phase interfaces. Herein, we present a wettability regulation strategy that modulates the triple-phase reaction zone in the catalyst layer of GDEs. This strategy was employed on a flow-through hollow fiber GDE coated with a Bi-embedded catalyst layer. Compared to other ex-situ methods (e.g., adding wetting agents) affecting the bulk of electrocatalysts or catalyst layer, we create distinctive hydrophilic-hydrophobic regions within the catalyst layer. Catalyst layer with hydrophilic-hydrophobic regions outperforms the fully hydrophilic one by facilitating the species transport, boosting triple-phase interface formation, and maximizing the active sites. This regulation strategy showed stable wettability during CO2RR cathodic conditions, evidenced by the direct measurement of penetration depth. The electrode with the regulated wettability exhibited over 80% catalyst utilization and 4 times higher formate partial current density (similar to 150 mA cm(-2) with FEformate > 90%) compared to the untreated electrode, outperforming other GDEs employed for CO2RR to formate in the same concentrations of bicarbonate. The finding of this versatile microenvironment regulation strategy can be extended to GDEs used for other gas-phase reactions.

Due to the ability to produce sustainably carbon-based chemicals and fuels, CO2 electrolysis and the closely related CO electrolysis are advancing rapidly from fundamental studies toward industrial applications.

We report a new strategy to improve the reactivity and durability of a membrane electrode assembly (MEA)-type electrolyzer for CO2 electrolysis to CO by modifying the silver catalyst layer with urea. Our experimental and theoretical results show that mixing urea with the silver catalyst can promote electrochemical CO2 reduction (CO2R), relieve limitations of alkali cation transport from the anolyte, and mitigate salt precipitation in the gas diffusion electrode in long-term stability tests. In a 10 mM KHCO3 anolyte, the urea-modified Ag catalyst achieved CO selectivity 1.3 times better with energy efficiency 2.8-fold better than an untreated Ag catalyst, and operated stably at 100 mA cm-2 with a faradaic efficiency for CO above 85% for 200 h. Our work provides an alternative approach to fabricating catalyst interfaces in MEAs by modifying the catalyst structure and the local reaction environment for critical electrochemical applications such as CO2 electrolysis and fuel cells.

Interactions of electrolyte ions at electrocatalyst surfaces influence the selectivity of electrochemical CO2 reduction (CO2R) to chemical feedstocks like CO. We investigated the effects of anion type in aqueous choline halide solutions (ChCl, ChBr, and ChI) on the selectivity of CO2R to CO over an Ag foil cathode. Using an H-type cell, we observed that halide-specific adsorption at the Ag surface limits CO faradaic efficiency (FECO) at potentials more positive than -1.0 V vs. reversible hydrogen electrode (RHE). At these conditions, FECO increased from I-90 %) in ChCl (at -0.75 +/- 0.06 Vvs. RHE) and ChI (at -0.78 +/- 0.17 V vs. RHE) could be achieved at a current density of 150 mA cm(-2) in a continuous flow-cell electrolyser with Ag nanoparticles on a commercial gas diffusion electrode. This study provides new insights to understand the interactions of anions with catalysts and offers a new method to modify electrocatalyst surfaces.