Selective Ion Transport Regulation Enables High Current Density CO2-to-C2+ Conversion in Acid.

Electrocatalytic CO ₂ Reduction over Bimetallic Bi-Based Catalysts: A Review

On the Conversion Efficiency of CO2 Electroreduction on Gold

Electrochemical ammonia synthesis: Mechanistic understanding and catalyst design

Effects of electrochemical active surface area of Cu on electrochemical CO2 reduction in acidic electrolyte using Cu nanoparticles on surfactant-treated carbon

The electrochemical carbon dioxide reduction reaction (ECDRR) driven by clean energy resources (such as wind, solar, etc.) to chemical feedstock and fuels is an attractive route to balance the carbon‐neutral cycle and for regenerating fuels. To date, the ECDRR has been the most promising technology for the conversion of carbon dioxide (CO2) to carbon‐building blocks, which has a huge market demand and increasing annual global production. Despite tremendous research, the conversion of CO2 into valuable fuels and chemicals is still challenging due to the highly inert and diverse CO2 reduction pathways towards high Faradaic efficiency, current density, and stability in the industrialization of ECDRR process. Herein, the most recent developments such as 1) the evaluation of the role of an electrocatalyst according to industrial production demands; 2) the performance of nanostructured electrocatalyst, electrolyte, and devices; 3) advantages and disadvantages of promising metals, such as Au, Ag, and Cu, and single‐atoms, such as Ni, Fe, and Co; and 4) the electrolyte effects, pH effects, and ion effects are described with a vision for ECDRR electrocatalysis towards industrialization. Finally, this review aims to offer forward‐looking, on‐going research/possible activities, together with future perspectives on the ECDRR process from a small‐scale production to industrialization.

The electrochemical carbon dioxide reduction reaction (CO2RR) offers a promising solution to mitigate carbon emission and at the same time generate valuable carbonaceous chemicals/fuels. Single atom catalysts (SACs) are encouraging to catalyze the electrochemical CO2RR due to the tunable electronic structure of the central metal atoms, which can regulate the adsorption energy of reactants and reaction intermediates. Moreover, SACs form a bridge between homogeneous and heterogeneous catalysts, providing an ideal platform to explore the reaction mechanism of electrochemical reactions. In this review, we first discuss the strategies for promoting the CO2RR performance, including suppression of the hydrogen evolution reaction (HER), generation of C1 products and formation of C2+ products. Then, we summarize the recent developments in regulating the structure of SACs toward the CO2RR based on the above aspects. Finally, several issues regarding the development of SACs for the CO2RR are raised and possible solutions are provided.

Planar Ni(II) porphyrinoid complexes have been widely used in electrochemical carbon dioxide reduction reaction and oxygen reduction reaction as well as hydrogen evolution reaction (HER). However, nonplanar Ni(II) tetra-pyrrolic complexes have not been thoroughly investigated thus far. In this study, three highly bent bis(dipyrrin) Ni(II) complexes have been synthesized to investigate their structure, electronic property, and electrocatalytic HER activities. Cyclic voltammetry and thin-layer UV-visible spectroelectrochemistry studies revealed four redox processes, yielding two reduced species as the final products. The ic/ip values of phenyl- and pentafluorophenyl-bearing bis(dipyrrin) Ni(II) complexes were >30 when trifluoroacetic acid was used as the proton source, and their Faradaic efficiencies for H2 generation were >93%. Density functional theory calculations of the HERs revealed low endothermic energies of bent bis(dipyrrin) Ni(II) complexes.

There is a growing need to utilize CO2 and realize a carbon-neutral society from the perspective of environmental problems caused by CO2 from fossil fuel-based processes. In this trend, electrochemical carbon dioxide reduction reaction (CO2RR), which converts CO2 to valuable fuels and chemicals with renewable energy, is attracting attention[1]. However, CO2RR has many challenges, including its low product selectivity. In particular, the hydrogen evolution reaction (HER), which occurs at the potential close to the standard electrode potential of CO2RR, reduces the selectivity of CO2RR, especially in aqueous electrolytes such as KHCO3 [2] [3]. Therefore, we focus on a concentrated electrolyte, which is used as a means of HER suppression in water-based Li-ion batteries[4], to improve the selectivity of CO2RR. A concentrated electrolyte is an electrolyte with a high salt concentration, which can improve the electrochemical stability of water by creating a specific water environment[5]. Furthermore, due to its high salt concentration, the effect of anions and/or cations may become significant[6][7]. However, there has been no detailed understanding of how the electrolyte concentration affects the complex reaction pathway of CO2RR.Here, we report the effect of concentrated electrolytes on the reaction process of CO2RR by directly observing reaction intermediates in situ while applying the potential. The product selectivity of CO2RR in 22.2, 42.0, and 61.7 mol kg– 1 of concentrated electrolyte was evaluated. Gas chromatography (GC) analysis confirms the suppression of HER in the series of concentrated electrolytes compared to 0.1 M KHCO3, a common aqueous electrolyte. In addition, an increase in the Faradaic efficiency of C2H4 was observed in ~ 42.0 mol kg– 1, implying a concentration-dependent change in the CO2RR reaction pathway (Fig.1). To elucidate the cause of the high C2H4 selectivity, in situ surface-enhanced infrared absorption spectroscopy (SEIRAS), which allows direct observation of the reaction intermediates, was performed. The results showed that as the electrolyte concentration was increased, the peaks at 1400 to 1500 cm– 1 region became more pronounced at low potential. We also observed the difference in the potential dependency for the intensity of CO adsorbates peak at 2100 cm–1 by electrolyte concentration. We will then discuss the effect of electrolyte concentration on the intermediates, unraveling the concentration-dependent change of the C2H4 selectivity. The work highlights the use of concentrated electrolytes to open up additional knobs for tuning the product selectivity of CO2RR, simply by designing an electrolyte component.[1] De Luna, P. et al, Science. 2019 364, 350.[2] Pan, F.; Yang, Y. Energy Environ. Sci. 2020, 13, 2275–2309.[3] Hori, Y. et al, Electrochim. Acta. 1994 39, 1833–1839.[4] Han, J. et al, Energy Environ. Sci. 2023 16, 1480.[5] Ko, S. et al, Electrochem. Commun. 2020 116, 106764.[6] Shin, S. J. et al, Nat. Commun. 2022 13, 5482.[7] Varela, A. S. et al, ACS Catal. 2016 6, 2136-2144. Figure 1

Development of efficient catalysts for electrochemical carbon dioxide reduction reaction (CO2RR) represents a great challenge in renewable energy research. Although noble metals have long been explored as catalysts for CO2RR, their reactivity and selectivity remain rather low owing to the competing hydrogen evolution reaction (HER). Here, this work proposes that noble metal monolayers (MLs) supported by transition metal carbides (TMCs) and nitrides (TMNs) can become exceptional CO2RR catalysts with much suppressed HER. This work shows that there is a direct, antibonding interaction between the hydrogen adsorbate and the TMC/TMN substrates, while such interactions between CO2RR intermediates and the substrates are absent. This difference enables dual‐site functionalization of the ML catalysts, which circumvents the energy scaling relations dictating the competition between CO2RR and HER. Consequently, it is possible to reduce the binding of the H adsorbate to suppress HER and simultaneously increase the binding of CO2RR intermediates to boost the CO2RR. This work identifies several Ag and Au‐based catalysts that are thermodynamically and electrochemically stable and exhibit high activity and selectivity toward the production of formic acid. In addition, this work predicts that higher order CO2RR products including methanol and ethylene can also be produced on selected catalysts.

Thin Films Fabricated by Pulsed Laser Deposition for Electrocatalysis

Unprecedented Lower Over-potential for CO2 Electro-reduction on Copper oxide Anchored to Graphene Oxide Microstructures

The electrochemical carbon dioxide reduction reaction (eCO2RR) using nitrogen-doped carbon (N-C) materials offers a promising and cost-effective approach to global carbon neutrality. Regulating the porosity of N-C materials can potentially increase the catalytic performance by suppressing the concurrence of the hydrogen evolution reaction (HER). However, the augmentation of porosity usually alters the active sites or the chemical composition of catalysts, resulting in intertwined influences of various structural factors and catalytic performance. In this study, incorporating secondary carbon sources into the metal-organic framework (MOF) precursor through nanocasting aimed to selectively enhance the mesoporous structure, allowing for deciphering this effect from other changes in the catalyst composition. Consequently, the developed N-C catalyst exhibited a significant surface area with abundant mesopores, leading to a maximum Faradaic efficiency (FE)for carbon monoxide(CO)of 95% at -0.50 V versus the reversible hydrogen electrode (vs. RHE). Furthermore, the FE for CO is enhanced across a wide potential range, surpassing previously reported metal-free N-C eCO2RR catalysts. The investigation reveals that constructing mesoporous structures can induce excellent CO2 catalysis by enhancing the accessibility of active sites while establishing an elevated local pH at these sites.

The electrochemical carbon dioxide reduction reaction (CO2RR) to generate feedstocks for chemical products (e.g., carbon monoxide, CO) offers a highly attractive method for achieving the closure of the carbon cycle. Ionic liquids (ILs)-functionalized Cu-based catalyst Cu2O-HKUST-1/IL1/PTFE was developed, configuring metal-organic frameworks(MOFs) based materials with high adsorption and multiple active sites. The modified electrocatalysts exhibited high specific surface area, strong CO2 adsorption capacity, abundant active sites, and fast charge transfer rate. The nucleophilic active site of deprotonation at the C2 site in imidazole ILs further improved the selectivity of proton migration and CO product generation, which was verified through DFT calculations for the low Gibbs free energy of the generated intermediate interactions. In addition, the hydrophobic interface constructed by PTFE facilitated the inhibition of the hydrogen evolution reaction (HER) and significantly improved the efficiency of CO2 electroreduction. The Cu2O-HKUST-1/IL1/PTFE catalyst manifested a high C1 Faraday efficiency (FE) up to 96.5% and in particular 92.7% for FECO at -1.7 V vs RHE. The present work provides an efficient strategy for configuring ILs-functionalized MOFs-based materials with good hydrophobic interfaces to enhance the efficiency of CO2 electroreduction to C1 products.

Efficient electrochemical CO2 reduction reaction on a robust perovskite type cathode with in-situ exsolved Fe-Ru alloy nanocatalysts

Electrochemical carbon dioxide reduction reaction (CO2RR) under strongly acidic conditions enables high CO2 utilization. However, especially in proton exchange membrane (PEM) electrode assembly reactors, achieving selective CO2RR in such environments remains challenging due to uncontrolled interfacial water diffusion at high current densities. Here, we develop a nickel-based heterogeneous molecular electrocatalyst (NiPc-NH2/CNT-SHP) featuring amino (-NH2) functional groups and grafted long-chain hydrophobic molecules. Under acidic conditions, -NH2 is in situ protonated to form amino cations (-NH3⁺). The positively charged -NH3⁺ groups and hydrophobic molecules effectively disrupt the protonated water (H3O+)-rich network, inhibiting the invasion of H3O+ and thereby suppressing the hydrogen evolution reaction, while enhancing selectivity for acidic CO2RR. The catalyst achieves nearly 100% Faradaic efficiency for CO at current densities from 50 to 400 mA cm-2, with approximately 76% CO2 utilization efficiency in a flow cell, and sustains over 80% selectivity for more than 200 h in a self-designed PEM-porous solid electrolyte reactor. These findings highlight interfacial water management as a key design principle for efficient acidic CO2 electroreduction.