Cu-In Dual Sites with Sulfur Defects toward Superior Ethanol Electrosynthesis from CO2 Electrolysis

The electrosynthesis of multi-carbon chemicals from excess carbon dioxide (CO2) is an area of great interest for research and commercial applications. However, improving both the yield of CO2-to-ethanol conversion and the stability of the catalyst at the same time is proving to be a challenging issue. Here it is proposed to stabilize active Cu(I) and In dual sites with sulfur defects through an electro-driven intercalation strategy, which leads to the delocalization of electron density that enhances orbital hybridizations between the Cu-C and In-H bonds. Hence, the energy barrier for the rate-limiting *CHO formation step is reduced toward the key *OCHCHO* formation during ethanol production, which is also facilitated by the combined Cu site enabling C-C coupling and In site with a higher oxygen affinity based on both thermodynamic and kinetic calculations. Accordingly, such dual-site catalyst achieves a high partial current density toward ethanol of 409 ± 15 mA cm⁻2 for over 120 h. Furthermore, a scaled-up flow cell is assembled with an industrial-relevant current of 5.7 A for over 36 h, in which the carbon loss is less than 2.5% and single-pass carbon efficiency is ≈19%.

Regulation Strategy of Nanostructured Engineering on Indium-Based Materials for Electrocatalytic Conversion of CO2

Electrochemical carbon dioxide reduction (CO2 RR), as an emerging technology, can combine with sustainable energies to convert CO2 into high value-added products, providing an effective pathway to realize carbon neutrality. However, the high activation energy of CO2 , low mass transfer, and competitive hydrogen evolution reaction (HER) leads to the unsatisfied catalytic activity. Recently, Indium (In)-based materials have attracted significant attention in CO2 RR and a series of regulation strategies of nanostructured engineering are exploited to rationally design various advanced In-based electrocatalysts, which forces the necessary of a comprehensive and fundamental summary, but there is still a scarcity. Herein, this review provides a systematic discussion of the nanostructure engineering of In-based materials for the efficient electrocatalytic conversion of CO2 to fuels. These efficient regulation strategies including morphology, size, composition, defects, surface modification, interfacial structure, alloying, and single-atom structure, are summarized for exploring the internal relationship between the CO2 RR performance and the physicochemical properties of In-based catalysts. The correlation of electronic structure and adsorption behavior of reaction intermediates are highlighted to gain in-depth understanding of catalytic reaction kinetics for CO2 RR. Moreover, the challenges and opportunities of In-based materials are proposed, which is expected to inspire the development of other effective catalysts for CO2 RR.

Ag+ -Doped InSe Nanosheets for Membrane Electrode Assembly Electrolyzer toward Large-Current Electroreduction of CO2 to Ethanol

It is an appealing approach to CO2 utilization through CO2 electroreduction (CO2 ER) to ethanol at high current density; however, the commonly used Cu-based catalysts cannot sustain large current during CO2 ER despite their capability for ethanol production. Herein, we report that Ag+ -doped InSe nanosheets with Se vacancies can address this grand challenge in a membrane electrode assembly (MEA) electrolyzer. As revealed by our experimental characterization and theoretical calculation, the Ag+ doping, which can tailor the electronic structure of InSe while diversifying catalytically active sites, enables the formation of key reaction intermediates and their sequential evolution into ethanol. More importantly, such a material can well work for large-current conditions in MEA electrolyzers with In2+ species stabilized via electron transfer from Ag to Se. Remarkably, in an MEA electrolyzer by coupling cathodic CO2 ER with anodic oxygen evolution reaction (OER), the optimal catalyst exhibits an ethanol Faradaic efficiency of 68.7 % and a partial current density of 186.6 mA cm-2 on the cathode with a full-cell ethanol energy efficiency of 26.1 % at 3.0 V. This work opens an avenue for large-current production of ethanol from CO2 with high selectivity and energy efficiency by rationally designing electrocatalysts.

Native frustrated Lewis pairs on core-shell In@InOxHy enhances CO2-to-formate conversion

Strategies to efficiently activate CO2 by strongly inhibiting the competitive hydrogen evolution reaction process are highly desired for practical applications of the electrochemical CO2 reduction technique. Here, we assembled a core-shell In@InOxHy architecture on carbon black by one-step reduction of NaBH4 as a CO2-to-formate catalyst with high selectivity. The stable CO2-to-formate reaction originates from the creation of steritic frustrated Lewis pairs (FLPs) on the InOxHy shell with In-OVs (OVs, oxygen vacancies) Lewis acid, and In-OH Lewis base. During CO2 reduction, the electrochemically stable FLPs are capable of first capturing and stabilizing protons to protonate FLPs to In-H Lewis acid and In-OH2 Lewis base due to its strong steric electrostatic field; then, CO2 is captured and activated by the protonated FLPs to selectively produce formate. Our results demonstrated that FLPs can be created on the surface of oxyphilic single-metal catalysts efficient in accelerating CO2 reduction with high selectivity.

Aligned InS Nanorods for Efficient Electrocatalytic Carbon Dioxide Reduction

Electrochemical CO₂ reduction technology can combine renewable energy sources with carbon capture and storage to convert CO₂ into industrial chemicals. However, the catalytic activity under high current density and long-term electrocatalysis process may deteriorate due to agglomeration, catalytic polymerization, element dissolution, and phase change of active substances. Here, we report a scalable and facile method to fabricate aligned InS nanorods by chemical dealloying. The resulting aligned InS nanorods exhibit a remarkable CO₂RR activity for selective formate production at a wide potential window, achieving over 90% faradic efficiencies from -0.5 to -1.0 V vs reversible hydrogen electrode (RHE) under gas diffusion cell, as well as continuously long-term operation without deterioration. In situ electrochemical Raman spectroscopy measurements reveal that the *OCHO* species (Bidentate adsorption) are the intermediates that occurred in the reaction of CO₂ reduction to formate. Meanwhile, the presence of sulfur can accelerate the activation of H₂O to react with CO₂, promoting the formation of *OCHO* intermediates on the catalyst surface. Significantly, through additional coupling anodic methanol oxidation reaction (MOR), the unusual two-electrode electrolytic system allows highly energy-efficient and value-added formate manufacturing, thereby reducing energy consumption.

All-solid-state WO3/TQDs/In2S3 Z-scheme heterojunctions bridged by Ti3C2 quantum dots for efficient removal of hexavalent chromium and bisphenol A

Ti₃C₂ quantum dots (TQDs) derived from ultrathin few-layered Ti₃C₂ nanosheets were served as the low-cost solid electron mediator of photogenerated carriers at the semiconductor interfaces, which could greatly reserve the reductive and oxidative reaction sites on the surface of heterojunctions and accelerate the reduction and oxidation reactions. The all-solid-state TQDs-bridge WO₃/TQDs/In₂S₃ Z-scheme photocatalysts exhibited extremely promoted photocatalytic reduction of Cr (VI) and photocatalytic oxidation of Bisphenol A (BPA) under visible light irradiation, which are 4 and 3 times higher than that of WO₃/In₂S₃ heterojunctions, respectively. The favorable photocatalytic activities of WO₃/TQDs/In₂S₃ should attribute to the effective electron transfer and charges separation with introduction of TQDs as the electron mediators in the Z-scheme system. In addition, the stability of WO₃/TQDs/In₂S₃ was investigated and the possible mechanisms during photo-reduction of Cr (VI) and photo-oxidation of BPA were proposed. This work provides a new strategy for fabrication of all-solid-state Z-scheme heterojunctions using Ti₃C₂ quantum dots as the low-cost solid electron mediator for efficient environmental remediation.

An industrial perspective on catalysts for low-temperature CO2 electrolysis

Electrochemical conversion of CO₂ to useful products at temperatures below 100 °C is nearing the commercial scale. Pilot units for CO₂ conversion to CO are already being tested. Units to convert CO₂ to formic acid are projected to reach pilot scale in the next year. Further, several investigators are starting to observe industrially relevant rates of the electrochemical conversion of CO₂ to ethanol and ethylene, with the hydrogen needed coming from water. In each case, Faradaic efficiencies of 80% or more and current densities above 200 mA cm^-2 can be reproducibly achieved. Here we describe the key advances in nanocatalysts that lead to the impressive performance, indicate where additional work is needed and provide benchmarks that others can use to compare their results.

Electrocatalysis for CO2 conversion: from fundamentals to value-added products

This timely and comprehensive review mainly summarizes advances in heterogeneous electroreduction of CO₂: from fundamentals to value-added products.

Aromatic Ester-Functionalized Ionic Liquid for Highly Efficient CO2 Electrochemical Reduction to Oxalic Acid

Electrochemical reduction of CO₂ into valuable chemicals is a significant route to utilize CO₂ resources. Among various electroreduction products, oxalic acid (H₂ C₂ O₄ ) is an important chemical for pharmaceuticals, rare earth extraction, and metal processing. Here, an aprotic aromatic ester-functionalized ionic liquid (IL), 4-(methoxycarbonyl) phenol tetraethylammonium ([TEA][4-MF-PhO]), was designed as an electrolyte for CO₂ electroreduction into oxalic acid. It exhibited a large oxalic acid partial current density of 9.03 mA cm^-2 with a faradaic efficiency (FE) of 86 % at -2.6 V (vs. Ag/Ag⁺ ), and the oxalic acid formation rate was as high as 168.4 μmol cm^-2  h^-1 , which is the highest reported value to date. Moreover, the results of density functional theory calculations demonstrated that CO₂ was efficiently activated to a -COOH intermediate by bis-active sites of the aromatic ester anion via the formation of a [4-MF-PhO-COOH]^- adduct, which finally dimerized into oxalic acid.

A Mn-N3 single-atom catalyst embedded in graphitic carbon nitride for efficient CO2 electroreduction

Developing effective catalysts based on earth abundant elements is critical for CO₂ electroreduction. However, simultaneously achieving a high Faradaic efficiency (FE) and high current density of CO (j_CO) remains a challenge. Herein, we prepare a Mn single-atom catalyst (SAC) with a Mn-N₃ site embedded in graphitic carbon nitride. The prepared catalyst exhibits a 98.8% CO FE with a j_CO of 14.0 mA cm^-2 at a low overpotential of 0.44 V in aqueous electrolyte, outperforming all reported Mn SACs. Moreover, a higher j_CO of 29.7 mA cm^-2 is obtained in an ionic liquid electrolyte at 0.62 V overpotential. In situ X-ray absorption spectra and density functional theory calculations demonstrate that the remarkable performance of the catalyst is attributed to the Mn-N₃ site, which facilitates the formation of the key intermediate COOH^* through a lowered free energy barrier.

Electroreduction of CO2 in Ionic Liquid-Based Electrolytes

Electroreduction of carbon dioxide (CO₂) to value-added chemicals and fuels is a promising approach for sustainable energy conversion and storage. Many electrocatalysts have been designed for this purpose and studied extensively. The role of the electrolyte is particularly interesting and is pivotal for designing electrochemical devices by taking advantage of the synergy between electrolyte and catalyst. Recently, ionic liquids as electrolytes have received much attention due to their high CO₂ adsorption capacity, high selectivity, and low energy consumption. In this review, we present a comprehensive overview of the recent progress in CO₂ electroreduction in ionic liquid-based electrolytes, especially in the performance of different catalysts, the electrolyte effect, as well as mechanism studies to understand the reaction pathway. Perspectives on this interesting area are also discussed for the construction of novel electrochemical systems.