One-step electrosynthesis of ethylene and ethanol from CO2 in an alkaline electrolyzer

There has been significant progress in the electrochemical reduction of CO2 since the seminal work of Hori et al. in 1985 demonstrating hydrocarbon production at copper cathodes. The introduction of gas diffusion electrode (GDE) and membrane electrode assembly (MEA) flow cells have demonstrated progress to produce C2 products (ethylene, ethanol and acetate) at current densities >150 mA cm-2 with Faradaic Efficiencies (FE) >50% at different types of Cu cathodes. Selectivity depends on several pathways and the intermediate binding strength of species like *CO, *CHO, *OCCO, and *OCCOH. Thus, there are opportunities to engineer or optimize product selectivity.The work advanced ethylene production through Cu-P0.065 electrocatalyst (Cuδ+ = 0.13), achieving 52% FE at 150 mA cm-2 in 0.1 M KHCO3, and remarkably improving to 70% FE in weakly acidic conditions (pH 6) while maintaining 64% FE at 250 mA cm−2. Electrolyte engineering demonstrated that larger alkali cations (Na+ to Cs+) effectively suppress hydrogen evolution from 31% to 4% while promoting C2 formation (45% to 89% FE). K+ concentration optimization (0.1-2M) further enhanced ethylene production, increasing FE from 42% to 65% at 4V while reducing HER from 48% to 20%. Mechanistic studies revealed K+ and OH- species accumulation near the electrocatalyst surface promotes C-C coupling through K+ and *OCCO intermediate interactions, while phosphorus doping enhances *CO generation and coupling.In terms of ethanol our work demonstrates that Cu-Sn0.03 electrocatalyst (Cuδ+ = 0.27) can achieve 48% FE at 350 mA cm-2 under alkaline conditions. A breakthrough in product separation was achieved through a dual-layer membrane configuration incorporating CEM and AEM. This system, using 1M KOH (pH 14) inner layer and 1M KOH+H3PO4 (pH 6) anolyte, reached 51.92% FE for ethanol with minimal anode crossover (<1.07% FE), enabling direct production of >8 wt% ethanol. Additionally, anion identity studies (PO4 2-, SO4 2-, and NO4 -) demonstrated consistent C2 efficiencies (61-65%) at fixed pH.In terms of acetate production, we show Cu2Se electrocatalyst (Cuδ+ = 0.47), demonstrating 40% FE for acetate at 350 mA cm-2. Notably, all electrocatalysts maintained exceptional stability over 250 hours with minimal degradation (0.02% FE loss/hour). These results show structure-function relationships of electrocatalysts in CO2 reduction and high levels of ethylene, ethanol, and acetate production; however, several critical barriers related to operating (viz. Energy) cost and durability remain. We conclude with a review of the state of the art and the needs for commercialization.

There has been significant progress in the electrochemical reduction of CO2 since the seminal work of Hori et al. in 1985 demonstrating hydrocarbon production at copper cathodes. The introduction of gas diffusion electrode (GDE) and membrane electrode assembly (MEA) flow cells have demonstrated progress to produce C2 products (ethylene, ethanol and acetate) at current densities >150 mA cm-2 with Faradaic Efficiencies (FE) >50% at different types of Cu cathodes. Selectivity depends on several pathways and the intermediate binding strength of species like *CO, *CHO, *OCCO, and *OCCOH. Thus, there are opportunities to engineer or optimize product selectivity.The work advanced ethylene production through Cu-P0.065 electrocatalyst (Cuδ+ = 0.13), achieving 52% FE at 150 mA cm-2 in 0.1 M KHCO3, and remarkably improving to 70% FE in weakly acidic conditions (pH 6) while maintaining 64% FE at 250 mA cm−2. Electrolyte engineering demonstrated that larger alkali cations (Na+ to Cs+) effectively suppress hydrogen evolution from 31% to 4% while promoting C2 formation (45% to 89% FE). K+ concentration optimization (0.1-2M) further enhanced ethylene production, increasing FE from 42% to 65% at 4V while reducing HER from 48% to 20%. Mechanistic studies revealed K+ and OH- species accumulation near the electrocatalyst surface promotes C-C coupling through K+ and *OCCO intermediate interactions, while phosphorus doping enhances *CO generation and coupling.In terms of ethanol our work demonstrates that Cu-Sn0.03 electrocatalyst (Cuδ+ = 0.27) can achieve 48% FE at 350 mA cm-2 under alkaline conditions. A breakthrough in product separation was achieved through a dual-layer membrane configuration incorporating CEM and AEM. This system, using 1M KOH (pH 14) inner layer and 1M KOH+H3PO4 (pH 6) anolyte, reached 51.92% FE for ethanol with minimal anode crossover (<1.07% FE), enabling direct production of >8 wt% ethanol. Additionally, anion identity studies (PO4 2-, SO4 2-, and NO4 -) demonstrated consistent C2 efficiencies (61-65%) at fixed pH.In terms of acetate production, we show Cu2Se electrocatalyst (Cuδ+ = 0.47), demonstrating 40% FE for acetate at 350 mA cm-2. Notably, all electrocatalysts maintained exceptional stability over 250 hours with minimal degradation (0.02% FE loss/hour). These results show structure-function relationships of electrocatalysts in CO2 reduction and high levels of ethylene, ethanol, and acetate production; however, several critical barriers related to operating (viz. Energy) cost and durability remain. We conclude with a review of the state of the art and the needs for commercialization.

Developing efficient carbon-based metal-free electrocatalysts can bridge the gap between laboratory studies and practical applications of CO2 reduction. However, along with the ambiguous understanding of the active sites in carbon-based electrocatalysts, carbon-based electrocatalysts with high selectivity and satisfactory stability for electroreduction of CO2 remain rare. Here, using the nitrogen rich silk cocoon as a precursor, carbon-based electrocatalysts with intrinsic defects can be prepared for efficient and long-term electroreduction of CO2 by a simple two-step carbonization. The obtained electrocatalyst can catalyze CO2 reduction to CO with a Faradaic efficiency of ~ 89% and maintain good selectivity for about 10 days. Particularly, our experimental studies suggest that in-plane defects are the main active sites on which the rate-determining step for CO2 reduction should be the direct electron transfer to CO2 but not the proton-coupled electron transfer. Further theoretical calculations consistently demonstrate that the intrinsic defects in carbon matrix, particularly the pentagon-containing defects, act as main active sites to accelerate the direct electron transfer for CO2 reduction. In addition, our synthetic approach can convert egg white into efficient catalysts for CO2 electroreduction. These findings, providing new insights into the biomass-derived catalysts, should pave the way for fabricating efficient and stable carbon-based electrocatalysts with catalytically active defects by using naturally abundant precursors.

Efficient Electrocatalytic CO2 Reduction to C2+ Alcohols at Defect-Site-Rich Cu Surface

An Extrinsic Faradaic Layer on CuSn for High-Performance Electrocatalytic CO ₂ Reduction

Modern industrialization is accompanied with the extensive usage of fossil fuels for energy demands and consequently, an excessive emission of CO2 into the atmosphere. To combat the injurious greenhouse effects, the CO2 electroreduction (CER) to feedstocks and fuels becomes an appealing approach to reducing CO2 emission and simultaneously producing useful products. It is generally recognized that the solid-catalyst/liquid-electrolyte/gaseous-CO2 triple-phase boundary is the key microstructure feature of CER, where CO2 molecules react with protons (H+) and e− and are reduced. Besides the intrinsic activity of catalyst itself and the accessibility of active sites, CER performance also strongly depends on the transport of H+ and CO2 molecules through electrolyte to catalyst surface. Apparently, the availability of H+ in aqueous solution can be readily achieved via H2O ionization, while the low solubility of CO2 limits the supply of CO2 to the catalyst surface. Moreover, previous study has demonstrated that complete depletion of CO2 on the catalyst surface can even occur when high overpotential is applied.1 In this regard, rationally designing the structure of catalyst to increase the concentration of CO2 at the triple-phase boundary is immensely significant for CER since this could overcome the limited diffusion of CO2 in aqueous medium.Recently, surface hydrophobicity engineering has been proved to be a wise tactic to increase the local CO2 concentration by trapping CO2 near the catalyst surface, thus improving CO2 electrolysis. For example, modification of the hydrophobic organics on catalyst surface could create triple-phase boundary and increase CO2 concentration on catalyst surface, these improved CER performance and simultaneously inhibited HER.2 Unfortunately, the insulative organics coated on the catalyst surface will sacrifice its activity, while some small pieces of organics may desorb from the surface or in the case of flow cell, these pieces can be flushed away by the fluid. Since most catalysts are in situ grown on carbon support with the advantages of rapid electron transfer and seamless contact,3, 4 it is possible to tailor the microenvironment around the catalyst through chemical modification of carbon support. For example, platinum-based catalysts supported on hydrophobic carbon with a desirable microenvironment display a state-of-the-art catalytic activity for oxygen reduction reaction.5 However, few studies have been conducted to investigate how the carbon support can be modified to create a favourable triple-phase boundary for CER.In this study, we have in situ grown Bi2O3 nanosheets (NSs) on two types of carbon materials, hydrophobic carbon nanofiber (Bi2O3@C/HB) and hydrophilic carbon nanofiber (Bi2O3@C/HL), respectively, and used them as the cathode catalysts for CER. Compared to Bi2O3@C/HL, the as-obtained Bi2O3@C/HB exhibits significantly boosted CER performances for formate formation with the high FEformate of ˃ 93% over an extremely wide potential window of 1000 mV, high formate partial current density (jformate ) of 102.1 mA cm−2 and high formate formation rate of 1905 μmol h−1 cm−2. Molecular dynamics (MD) simulations together with electrochemical measurements reveal that the hydrophobic carbon support can create a hydrophobic microenvironment by avoiding the formation of hydrogen bond. This increases the local CO2 concentration and pH, both contributing to the enhancement of the overall CER. We believe that the findings from this work can provide significant guidelines for designing highly active CER catalysts and showcase a promising approach to improving other types of electrolysis involving gas phase. Raciti, D.; Mao, M.; Park, J. H.; Wang, C., Mass transfer effects in CO2 reduction on Cu nanowire electrocatalysts. Catal. Sci. Technol. 2018, 8, 2364-2369.Wang, J.; Cheng, T.; Fenwick, A. Q.; Baroud, T. N.; Rosas-Hernández, A.; Ko, J. H.; Gan, Q.; Goddard Iii, W. A.; Grubbs, R. H., Selective CO2 Electrochemical Reduction Enabled by a Tricomponent Copolymer Modifier on a Copper Surface. J. Am. Chem. Soc. 2021, 143, 2857-2865.Liu, S.; Lu, X. F.; Xiao, J.; Wang, X.; Lou, X. W., Bi2O3 nanosheets grown on multi‐channel carbon matrix to catalyze efficient CO2 electroreduction to HCOOH. Angew. Chem., Int. Ed. 2019, 58, 13828-13833.Li, F.; Chen, L.; Knowles, G. P.; MacFarlane, D. R.; Zhang, J., Hierarchical mesoporous SnO2 nanosheets on carbon cloth: a robust and flexible electrocatalyst for CO2 reduction with high efficiency and selectivity. Angew. Chem., Int. Ed. 2017, 56, 505-509.Zhao, Z.; Hossain, M. D.; Xu, C.; Lu, Z.; Liu, Y.-S.; Hsieh, S.-H.; Lee, I.; Gao, W.; Yang, J.; Merinov, B. V., Tailoring a Three-Phase Microenvironment for High-Performance Oxygen Reduction Reaction in Proton Exchange Membrane Fuel Cells. Matter 2020, 3, 1774-1790.

Understanding the molecular dynamics on buried electrodes is of significant interest in electrochemistry. There is a big gap of knowledge in the CO2 electroreduction mechanism due to the limitations to access to the liquid-metal interface. Vibrational Sum Frequency Spectroscopy (VSFS) is a non-invasive and surface sensitive technique, with molecular level detection that can be used to probe electrochemical reactions occurring on the electrolyte-electrode interface [1]. In this study, we observed the CO2 electroreduction to CO in ionic liquid on poly Ag using VSFS synchronized with cyclic voltammetry. In order to follow the CO2 reaction in situ on the ionic liquid-Ag interface, the CO, CO2 and imidazolium vibrational modes (resonant SFS) were monitored as a function of potential. We identified at which potential the CO was produced and how the EMIM+-BF4 - played an important role in the electron transfer to the CO2, lowering the intermediate, CO2 - , energy barrier. We also present a new approach to reveal the double layer dynamics to the electrostatic environment by the study of the nonresonant SFS as a function of potential. In this analysis, we observed a strong third order effect in the susceptibility of the high electric field created in the double layer [2]. Finally, we discuss the intrinsic technical difficulties of probing deeply buried electrodes, as the IR absorption from the species of the electrolyte and how we tackled this problem. Note: why do we specifically study this electrochemical cell? Ionic liquids (ILs) attracted a wide attention within the electrochemical community due to their unique properties; such a high charge density, stable electrolytes and low volatility. In particular, imidazolium-based ILs were proposed as a promising electrolyte to use in CO2 fuel reactors, due to the CO2 high solubility. These gas flow-electrochemical cells, convert the CO2 into useful products such a CO, methane, ethanol [3]. The development of this technology can address two important environmental problems: the excess of CO2 in the atmosphere and the use of a different energy sources than fossil fuels for transportation. However, CO2 electroreduction is energetically very expensive, and higher energetic efficiency and reaction rates need to be fulfilled to become feasible [4]. Previous studies have shown, CO2 electroreduction in a water mixture with imidazolium–based ILs on Ag nanoparticles at lower overpotential [5]. Our study help to understand the dynamics of the ionic liquid at electrified interfaces and the influence in the CO2electroreduction to improve these gas electrochemical reactors. [1] (a) Bain, C. D.; J. Chem. Soc., Faraday Trans., 1995, 91, 1281. (b) Tadjeddine, A.; Vidal, F.; In-situ Spectroscopic Studies of Adsorption at the Electrode and Electrocatalysis, Elsevier Science B.V., Amsterdam,2007, pp. 273-298. [2] (a) Eisenthal, K. B.; Chem. Rev.; 1996, 96 (4): 1343. (b) Koelsch, P.; Muglali, M. I.; Rohwerder, M. and Erbe, A.; J. Opt. Am. B, 2013, 30 (1), 219. [3] Jhong, H.-R. M.; Ma, S.; Kennis, P. J. A.; Curr. Opin. Chem. Eng. 2013, 2: 191. [4] Whipple, D. T. & Kenis, P. J. A.; J. Phys. Chem. Lett.; 2010, 1 (24), 3451. [5] Rosen, B. A.; Salehi-Khojin, A.; Thorson, M. R.; Zhu, W.; Whipple, D. W., Kenis, P. J. A.; and Masel, R.I.; Science, 2011, 334 (6056), 643.

The electroreduction of CO(2), driven by renewable electricity, can be used to sustainably generate synthetic fuels and chemical feedstocks. Long carbon chain molecules are of particular interest due to their high energy densities and utilities. However, to date, most of the CO(2) reduction products formed are limited to C2 and C3. Herein, we discuss the development of electrocatalysts for the reduction of CO(2) to long-chain oxygenates and hydrocarbons, and their underlying reaction mechanisms.CO(2) electroreduction has been previously reported to yield a range of carbonaceous products including alcohols, hydrocarbons and carboxylic acids. Interestingly, esters, an important family of organic compounds, have not been formed. We show how C3–C6 acetate esters could be produced from CO reduction in a membrane electrode assembly (MEA) cell. The near water-free reaction environment and the high local pH in the MEA played key roles in forming the esters with a Faradaic efficiency of 22 % and a current density up to −55 mA cm−2. We also disclose that inorganic nickel oxygenate (INO)-derived electrocatalysts can reduce CO2 to linear and branched C3-C6 hydrocarbons with Faradaic efficiencies up to 6.5%. We identified Niδ+ active sites which bind CO moderately. Our results show that Ni atom polarization to be important in hindering CO poisoning of nickel and thus facilitating CO2 reduction to a wider pool of valuable products.Finally, we show how MgAl layered double hydroxide (LDH) nanosheets ‘House-of-cards’ structures help to disperse CuO-derived Cu (OD-Cu) catalysts. The porous structures formed enhanced CO gas percolation through the catalyst layer. OD-Cu dispersed by the ‘House-of-cards’ structures catalysed CO electroreduction to C2+ products with a partial current density that is an order of magnitude higher than that shown by the unsupported OD-Cu.

Background: Many studies have been conducted on tutor performance in problem-based curricula. In the past, the implicit assumption behind these studies was that tutor performance is a relatively stable characteristic. More recent studies demonstrate that a tutor's performance may be dependent on other circumstances, such as the level of structure in the curricular materials. The aim of this study was to investigate whether a tutor's performance is also dependent on the tutorial group's productivity. Purpose: The idea is that low-productive tutorial groups require much more input from a tutor than high-productive groups. In the problem-based curriculum under investigation, most tutors guide 2 tutorial groups within the same unit. A salient finding in this problem-based curriculum was that some tutors who guide 2 tutorial groups within the same unit have discrepancies in their tutor performance across the 2 groups. This finding might be explained by differences in both tutorial groups. In this study, first the scope of the discrepancy phenomena was studied. Second, the relation between the tutor's performance and the tutorial group's productivity was studied. Methods: The data set for this study included 136 tutors who, in total, ran 272 tutorial groups (each tutor ran 2 groups per unit). The analyses were conducted at the tutorial group level. Students were asked to judge the performance of their tutor. Low, medium, and high levels of tutor performance were distinguished. Tutors who were qualified as "low level of performance" in one tutorial group and "medium level of performance" in the other tutorial group were considered to have a discrepancy in their tutor performance: "discrepancy tutors." The same holds for tutors with medium level of performance in one group and high level of performance in the other group or low level of performance in one group and high level of performance in the other group. All other tutors were considered "nondiscrepancy tutors." The nondiscrepancy tutors had equal levels of performance in both groups: a low, medium, or high level. For each type of tutor (discrepancy tutors and nondiscrepancy tutors) the average tutorial group's productivity score was computed. Results: The results show that 39% of the tutors were classified as discrepancy tutors. In addition, it was found that a discrepancy tutor with a low level of tutor performance in one group also had a low productivity score in this group, whereas a high level of tutor performance corresponds with a high level of the tutorial group's productivity. Furthermore, the results show that nondiscrepancy tutors with a high level of tutor performance receive high tutor performance scores, irrespective of the tutorial group's level of productivity. Conclusions: These findings demonstrate that the tutorial group's productivity is another influencing factor in determining tutor performance. Low-productive groups require much more input from a tutor than high-productive groups. Nondiscrepancy tutors with consistent low levels of tutor performance and discrepancy tutors lack certain competencies that are needed when being confronted with a low-productive tutorial group. Nondiscrepancy tutors with a high level of tutor performance, on the contrary, know how to deal with low-productive tutorial groups, due to which their tutor performance is high irrespective of the tutorial group's productivity. Thus, a tutor's performance seems to be part tutor specific and part situation specific (i.e., dependent on the group's productivity).

The electroreduction of greenhouse gas CO 2 into high‐value‐added chemicals using renewable electricity is a promising way to mitigate climate change and realize carbon cycling. Atomically precise thiolate‐protected gold nanoclusters have shown great potential for selective electrochemical conversion of CO 2 toward CO due to their quantum confinement effect and unique electronic structures. Additionally, the atomic precision of gold nanocluster is advantageous for investigating the CO 2 reduction mechanism, which is typically challenging to understand due to the complexity of the catalytic interface, and unknown structure of the active site in more conventional catalysts. By summarizing CO 2 reduction catalyzed by gold nanoclusters, we aim to identify key factors that contribute to the activity, selectivity, and stability of nanocluster catalysts, as well as elucidate the CO₂ reduction pathway, thereby contributing to the design of more active and selective nanocluster catalysts for CO 2 reduction.

The production of syngas by traditional processes such as steam methane reforming is energetically expensive and leads to substantial CO2 emissions. This strongly motivates the development of CO2 electroreduction at ambient conditions. As a family of non-precious metal catalysts, transition metal-nitrogen-carbon electrocatalysts are cost effective and highly selective towards syngas production1,2. In this presentation, we will show our current research into mono and bi-metallic nitrogen-doped carbon (M-N-C, M = Fe, Mo or FeMo) electrocatalysts for syngas production. The electrocatalyst composition (i.e. the Fe:Mo ratio in the bimetallic electrocatalyst) was tuned, in combination with the potential applied, to control the selectivity and therefore the electrocatalyst’ ability to generate syngas. We show that a higher ratio of iron to molybdenum leads to an increase in selectivity to CO over H2 production. We show a greatly improved production rate for CO using traditional Fe-N-C which maxes out at a CO partial current density higher than that of commercial Ag nanoparticles (jco= -30.9 mA/cm2 geo at -1.1 VRHE) using a custom-built flow cell. The difficulties and importance of considering intrinsic catalytic activity is stressed to compare electrocatalytic activity. Apart from catalyst composition, reaction conditions can also substantially alter the electrochemical CO2/H2O co-electrolysis3. The catalyst composition can be used as an engineering control for the desired product selectivity by using a variable precursor metallic ratio in bi-metallic M-N-C catalysts. Potential control may be used alongside variations in reaction conditions for the dynamic control over the selectivity to syngas. Reference Delafontaine, L., Asset, T., & Atanassov, P. (2020). Metal–Nitrogen–Carbon Electrocatalysts for CO 2 Reduction towards Syngas Generation. ChemSusChem, 13(7), 1688–1698. Varela, A. S., Ranjbar Sahraie, N., Steinberg, J., Ju, W., Oh, H.-S., & Strasser, P. (2015). Metal-Doped Nitrogenated Carbon as an Efficient Catalyst for Direct CO2Electroreduction to CO and Hydrocarbons. Angewandte Chemie, 127(37), 10908–10912. Pan, F., & Yang, Y. (2020). Designing CO2 reduction electrode materials by morphology and interface engineering. Energy & Environmental Science, 13(8), 2275–2309. Figure 1

INTRODUCTION The demand of renewable energy is increasing, yet fluctuating power supply is one of the problems. Therefore, technology for energy storage such as alkaline water electrolysis is required. When an alkaline water electrolyzers is powered by renewable energy, electrodes degrade due to reverse current generated on shutdown.We have reported self-repairing catalysts based on hybrid cobalt hydroxide nanosheets (Co-ns), and β-FeOOH nanorods (Fe-nr).[1,2] Our previous studies showed that Co-ns formed thick catalyst layer with highly conductive framework, whereas Fe-nr formed a thin layer with much higher OER activity than that of Co-ns. With these features, we have designed the self-repairing supported composite catalysts[3] where colloidal assembly can be electrochemically deposited to form a composite catalyst layer, in which CoOOH nanosheets form a mesoporous network and Fe-nr is distributed on the surface of the CoOOH nanosheets as a supported catalyst.In this study we report and discuss about the deposition kinetics of composite catalyst on the electrodes by cyclic and continuous deposition protocol and compared the durability and OER activity of composite catalyst via ADT (accelerated degradation test) protocol for up to 2000th cycles. EXPERIMENTAL Co-ns [1] and Fe-nr[2] were synthesized according to the literature. Electrochemical tests were performed in a 1.0 M KOH, using a PFA three-electrode cell. A nickel plate, a nickel coil, and a reversible hydrogen electrode were used as the working, counter, and reference electrodes, respectively. The Co-ns dispersion, Fe-nr dispersion, or composite (each concentration of Co-ns catalyst is 40 ppm and those of Fe-nr catalyst varies from 5 ppm to 60 ppm) was added in the electrolyte. Catalysts were deposited by the following process: Cyclic Protocol[1,2] i) chronopotentiometry at 800 mA cm– 2 for 30 min, ii) cyclic voltammetry (CV) between 0.5 and 1.8 V vs. RHE at 5 mV s– 1, iii) CV between 0.5 and 1.6 V vs. RHE at 50 mV s– 1, and iv) electrochemical impedance spectroscopy at 1.6 V vs. RHE. and i)–iv) were repeated 20 times, and new protocol i.e. Continuous Protocol i) chronopotentiometry at 1600 mA cm– 2 for 18 hrs. The measurements ii)–iv) were performed after that. Furthermore, an accelerated durability test (ADT)[4] was conducted 2000 cycles to examine the degradation. RESULTS AND DISCUSSION The OER polarization curves during the electrolysis are shown in the Fig. 1. The OER overpotential at 100 mA cm–2 (η 100) of the composite catalyst (Co-ns 40 ppm + Fe-nr 5 ppm) is 266 mV after 18 hrs. of electrolysis. It is best among all the experiment performed as shown in Fig 2. The catalysts prepared by the continuous protocol tend to show lower Tafel slopes than those by the cyclic protocol.The CV curves at 50 mV/s during the electrolysis is shown in Fig 3, showing the shift of peaks due to Co2+/3+ to higher potential in the cyclic protocol. Meanwhile, the deposition amount of Co-ns (m Co)[5] as a function of the concentration of Fe-nr is shown in Fig. 4. It shows that the m Co value of sample (Co-ns 40 ppm + Fe-nr 5 ppm) via the continuous protocol is 302 µg cm– 2 and that via the cyclic protocol is 42 µg cm– 2. The deposition amount is much higher in the continuous protocol than in the cyclic protocol, probably because a partial structural change of CoOOH[6] into Co3O4 by repeated redox processes lowers the reactivity of CoOOH nanosheets to connect with Co-ns in the subsequent cycles.The results of ADT with the composite catalyst (Co-ns 40 ppm + Fe-nr 5 ppm) prepared via the continuous protocol and the cyclic protocol (Fig. 5) depicts that the continuous protocol shows higher activity up to 2000th cycles without loss of durability.In conclusion, the continuous protocol shows higher deposition amount of composite catalyst than the cyclic protocol. During ADT protocol, it also shows higher activity than the Fe-nr only, Co-ns only and composite catalyst deposited via the cyclic protocol. Therefore, the redox reaction of catalysts should be minimized during the initial catalyst deposition process to form thicker and durable catalyst layer. This work was supported by the JSPS KAKENHI (grant number 24K01580). REFERENCE [1] Y. Kuroda et al., Electrochem. Acta. 323, 1348122 (2019).[2] Y. Kuroda et al., J. Sol-Gel Sci. Technol., 104, 647 (2022).[3] Y. Kuroda et al., Adv. Energy Sust . Res. 2400196 (2024).[4] A. Haleem et al., Electrochemistry 89, 186 (2021).[5] R. Nakajima et al., ChemSusChem,16, e202300384 (2023).[6] M. Hamdani et al J . A ppl. E lectrochem. 18, 568(1988). Figure 1

Machine learning accelerates the screening of single-atom catalysts towards CO2 electroreduction

Alkaline water electrolysis (AWE) is at a stage of high technological maturity, and modern pressurized designs have mitigated the weaknesses of now-outdated atmospheric electrolyzers. For instance, pressurized systems now deliver high hydrogen outputs and can efficiently adjust to rapid changes in power loads. These improvements were, in part, made possible through significant reductions to internal ohmic losses coming from improved gas separators, shorter distances between electrodes, and increased operating temperatures.From an industrial point of view, the critical parameter to optimize is the full stack voltage. The stack voltage is tightly bound to the individual cell voltage and can thus be lowered by employing more efficient electrocatalysts. However, reducing the cell voltage by raising the temperature of operation—thereby improving both reaction kinetics and the conductivity of the KOH electrolyte—can be of similar or even higher importance (e.g., ca. 4.5 mV/˚C, Figure 1) [1]. Therefore, stability under operation at elevated temperatures must be considered when evaluating novel hydrogen and oxygen evolution reaction catalysts for AWE. Else, a novel catalyst risks becoming the bottleneck in the pursuit of higher operating temperatures, limiting its applicability for large-scale electrolysis [2]. Many assessments of novel AWE catalysts are still carried out at room temperature in diluted electrolytes and at low current densities [3]. In the harsher conditions of an electrolyzer, catalysts experience higher dissolution rates and are subject to higher mechanical stress from, for instance, the aggressive bubble evolution. This gap hinders the transfer of catalyst developments from academia to industrial research laboratories and, ultimately, to practical applications.In this work, we attempted to narrow that gap by conducting electrochemical measurements under more application-oriented conditions (i.e., 80-120 °C and 8-11 M KOH). We evaluated the HER activity and the robustness of high-surface-area electrodes produced through controlled leaching of bimetallic nickel-based alloys. A parametric study of the overpotential and robustness as a function of electrochemically active surface area was enabled by varying the synthesis parameters of a Raney-type preparation. Direct coupling to renewable energy sources requires the electrolyzer to frequently and rapidly shut off and on. This intermittent operation induces additional stress on the electrodes as the catalysts transition through different redox states, which is often overlooked in AWE electrocatalyst research. To track redox, compositional, and morphological changes, we used ex situ X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy. At the same time, the dissolution and redeposition of ionic species were monitored using inductively coupled plasma mass spectrometry. By matching the characterization data with the evolution of the overpotential until complete deactivation, we gained an understanding of the degradation mechanisms in high-surface-area nickel-based electrodes. These results shed light on the challenges and prospects of this promising class of electrocatalysts for alkaline HER under industrial conditions.Acknowledgement:This work is partly funded by the Innovation Fund Denmark (IFD) under File No. 1044-00162B.

CO2 electroreduction is a promising technique to convert renewable electricity and CO2 to high-value fuels and chemicals. Selectivity, energy efficiency, carbon efficiency and sustainability are the criteria for CO2 electroreduction techniques suitable for industrial application. With alkaline and neutral electrolytes, carbonate formation from CO2 leads to low carbon efficiency. High energy consumption to regenerate alkaline electrolyte and high resistance of neutral electrolyte cause low energy efficiency. Recently, CO2 reduction with acidic electrolyte becomes a hot topic due to its potential to increase carbon efficiency and energy efficiency. Improving the selectivity towards CO2 reduction is challenging in acidic condition. Diverse approaches were proposed to suppress H+ reduction and promote CO2 reduction. However, fundamental issues about cation effect and local pH effect on CO2 reduction in acidic condition are still under debate. Moreover, bicarbonate precipitation in gas diffusion electrode limits the sustainability with acidic electrolyte. This review tries to rationalize the reported strategies to improve the selectivity towards CO2 reduction in acidic condition from mass transport and electrode reactions. Different approaches, including adding alkali cations, surface decoration, nanostructuring, and electronic structure modulation, are designed based on these two aspects. This review also introduces the recent progress in CO2 electroreduction with metal cation-free acidic electrolyte. This strategy is deemed to improve the sustainability.