Suppressing Hydrogen Evolution Research Articles

Computational evaluation of CO2 conversion into formic acid via a novel adsorption mechanism on metal-free B4C12

The electrochemical reduction of CO2 (CO2RR) to formic acid (HCOOH) is a promising approach to harness renewable energy for the production of value-added chemicals and contribute to carbon cycling. The search for cost-effective and efficient metal-free electrocatalysts is critical for realizing industrial applications. However, limited literature is available on this topic, primarily because the significant challenge of efficiently activating inert CO2 remains unresolved. In this study, we have designed and applied a novel boron carbide (B4C12) monolayered cage as an electrocatalyst for CO2RR to produce HCOOH. B4C12 exhibits exceptional electronic, dynamic, and thermodynamic stability. Through comprehensive density functional theory computations, we have observed that B4C12 rapidly and stably adsorbs CO2 in a unique η3(O, C, O)-CO2 configuration, resulting in excellent CO2RR activity with a low limiting potential (–0.38 V) and suppressed hydrogen evolution reaction. Our mechanistic investigations reveal that B4C12 donates electrons to facilitate the bending of CO2, anchoring it onto the curved surface effectively. Additionally, the C atom in the η3(O, C, O)-CO2 configuration attracts H+ + e− pairs through its active p electron, leading to the observed low limiting potential. This study not only successfully designs a novel class of metal-free electrocatalysts but also provides a promising strategy for advancing CO2RR research in the future.

Elucidating key mechanistic processes during acidic CO2 electroreduction on gas diffusion electrodes towards stable production of formic acid

The electrochemical reduction of CO2 using renewable electricity could be a sustainable alternative to produce formic acid. Although using bulk acidic electrolyte offers system and downstream processing benefits, neutral to alkaline electrolyte systems prevail due to challenge suppressing hydrogen evolution in acidic environment. In recent years, it has been shown that HER could be mitigated by confining the OH- being generated and constraining the movement of H3O+ towards reaction surface, thereby producing an alkaline reaction environment within the electrode. Herein, we have demonstrated how a porous and highly hydrophobic Bi-based gas diffusion electrode enables remarkably efficient bulk acidic electrolysis. Importantly, the local alkaline reaction environment has been proven via electrochemical impedance spectroscopy and pH visualization. Furthermore, optical monitoring of electrolyte conditions through a transparent cell sheds light on the CO2 recovery process in the acidic system, promoting a better technical practice in handling with electrochemical cells and CO2 recirculation. Finally, HCOOH accumulation as the key degradation reason is unveiled through investigation into the impact of operating modes on the stability at high current density, where earlier studies failed to adequately address. It is believed that this valuable insight could facilitate stable and efficient formic acid production in future work.

Attenuating Water Activity Through Impeded Proton Transfer Resulting from Hydrogen Bond Enhancement Effect for Fast and Ultra‐Stable Zn Metal Anode

AbstractThe high activity of water molecules induces notorious side reactions that seriously impair the stability of the Zn metal anode. Inspired by the mechanism of proton transfer in an aqueous solution, ectoine (ET) with a kosmotropic effect is first introduced into the typical aqueous electrolyte of aqueous zinc‐ion batteries (ZIBs). The hydrogen bond enhancement brought by the ET additive increases the energy barrier for the reconfiguration of hydrogen bonds, thereby impeding the hopping transport of protons based on the Grotthuss mechanism. The inhibited hydrogen evolution reaction (HER) by impeded proton transfer is strongly proved by in situ electrochemical gas chromatography (EC‐GC). The distinctive hydrogen bond enhancement effect of ET results in remarkably improved Zn anode stability while maintaining fast reaction kinetics. Consequently, the Zn//Zn symmetric cell delivers an ultra‐long cycle life of 5700 h 1 mA cm−2/1 mAh cm−2 and 2000 h at 5 mA cm−2/5 mAh cm−2 with lower voltage hysteresis, extending a cycling life by >27 and 24 times without sacrificing reaction kinetics.

Electroreduction of Nitrite to Ammonia Over Ni1Ru Single‐Atom Alloys

AbstractElectroreduction of nitrite to ammonia (NO2RR) holds great promise for concurrently achieving efficient NH3 electrosynthesis and wastewater purification. This study first develops Ni1Ru single‐atom alloys as an efficient and robust NO2RR catalyst. Extensive experiments and theoretical computations reveal that isolated Ni atoms electronically couple their adjacent Ru atoms to render Ni1Ru with high thermodynamic stability, boosted NO2−‐to‐NH3 hydrogenation energetics and suppressed hydrogen evolution. As a result, Ni1Ru assembled in a flow cell shows an exceptional NH3 yield rate of 37.5 mg h−1 cm−2 with an NH3‐Faradaic efficiency of 93.9% at a high current density of 312.3 mA cm−2, representing one of the highest NO2RR performances ever reported.

Interfacial Modification of a Zn Anode by Amorphous Se toward Long-Life and Hydrogen Evolution-Free Aqueous Rechargeable Batteries.

The Zn anode in rechargeable aqueous Zn-ion batteries suffers from hydrogen gas evolution and dendrite growth, which are critical issues that make the battery impractical. Here, the Zn anode performance is greatly improved by coating an amorphous selenium overlayer with a simple chemical bath reaction process. The reduction of SeO32- ions by the Zn metal leads to the formation of an amorphous Se layer, and the optimal reaction time that determines the thickness of the Se coating as well as the Zn anode performance is found to be 2 h. The symmetric cell using Zn@Se exhibits improved rate performance and an ultralong cycle life of 4500 h after being tested at 1 mA cm-2 and 1 mAh cm-2, respectively. Compared to the bare Zn anode, the Zn@Se anode leads to a larger Zn2+ transference number and reduced charge transfer resistance. The button-type MnO2∥Zn@Se full cell exhibits higher capacity and a much longer cycle life compared to the counterpart using a bare Zn anode. Also, pouch-type MnO2∥Zn@Se full cells with a high capacity of 9.7 mAh cm-2 are made to demonstrate the inhibition of hydrogen evolution and practical applications. It is found that the in situ formation of an amorphous ZnO nanosheet network induced by the amorphous Se overlayer plays a key role in enhancing the Zn anode performance.

Suppressing hydrogen evolution and eliminating sulfation in lead-carbon batteries via potential-matching g-C3N4@rGO nanosheets

Suppressing hydrogen evolution and eliminating sulfation in lead-carbon batteries via potential-matching g-C3N4@rGO nanosheets

Surface-immobilized cross-linked cationic polyelectrolyte enables CO2 reduction with metal cation-free acidic electrolyte

Electrochemical CO2 reduction in acidic electrolytes is a promising strategy to achieve high utilization efficiency of CO2. Although alkali cations in acidic electrolytes play a vital role in suppressing hydrogen evolution and promoting CO2 reduction, they also cause precipitation of bicarbonate on the gas diffusion electrode (GDE), flooding of electrolyte through the GDE, and drift of the electrolyte pH. In this work, we realize the electroreduction of CO2 in a metal cation-free acidic electrolyte by covering the catalyst with cross-linked poly-diallyldimethylammonium chloride. This polyelectrolyte provides a high density of cationic sites immobilized on the surface of the catalyst, which suppresses the mass transport of H+ and modulates the interfacial field strength. By adopting this strategy, the Faradaic efficiency (FE) of CO reaches 95 ± 3% with the Ag catalyst and the FE of formic acid reaches 76 ± 3% with the In catalyst in a 1.0 pH electrolyte in a flow cell. More importantly, with the metal cation-free acidic electrolyte the amount of electrolyte flooding through the GDE is decreased to 2.5 ± 0.6% of that with alkali cation-containing acidic electrolyte, and the FE of CO maintains above 80% over 36 h of operation at −200 mA·cm−2.

Titania-supported Cu Single Atom Catalyst for Electrochemical Reduction of Acetylene to Ethylene at Low-Concentrations with Suppressed Hydrogen Evolution.

Electrochemical acetylene reduction (EAR) is a promising strategy for removing acetylene from ethylene-rich gas streams. However, suppressing the undesirable hydrogen evolution is vital for practical applications in acetylene-insufficient conditions. Herein, weimmobilized Cu single atoms on anatase TiO2 nanoplates (Cu-SA/TiO2 ) for electrochemical acetylene reduction, achieving an ethylene selectivity of ∼97% with a 5vol.% acetylene gas feed (Ar balance). At the optimal Cu single atom loading, Cu-SA/TiO2 wasable to effectively suppress HER and ethylene over-hydrogenation even when using dilute acetylene (0.5vol.%) or ethylene-rich gas feeds, delivering a 99.8% acetylene conversion, providing a turnover frequency of 8.9 × 10-2 s-1 , which is superior to other EAR catalysts reported to date. Theoretical calculations showed that the Cu single atoms and the TiO2 support acted cooperatively to promote charge transfer to adsorbed acetylene molecules, whilst also inhibiting hydrogen generation in alkali environments, thus allowing selective ethylene production with negligible hydrogen evolution at low acetylene concentrations. This article is protected by copyright. All rights reserved.

A Bio‐Inspired Trehalose Additive for Reversible Zinc Anodes with Improved Stability and Kinetics

AbstractThe moderate reversibility of Zn anodes, as a long‐standing challenge in aqueous zinc‐ion batteries, promotes the exploration of suitable electrolyte additives continuously. It is crucial to establish the absolute predominance of smooth deposition within multiple interfacial reactions for stable zinc anodes, including suppressing side parasitic reactions and facilitating Zn plating process. Trehalose catches our attention due to the reported mechanisms in sustaining biological stabilization. In this work, the inter‐disciplinary application of trehalose is reported in the electrolyte modification for the first time. The pivotal roles of trehalose in suppressed hydrogen evolution and accelerated Zn deposition have been investigated based on the principles of thermodynamics as well as reaction kinetics. The electrodeposit changes from random accumulation of flakes to dense bulk with (002)‐plane exposure due to the unlocked crystal‐face oriented deposition with trehalose addition. As a result, the highly reversible Zn anode is obtained, exhibiting a high average CE of 99.8 % in the Zn/Cu cell and stable cycling over 1500 h under 9.0 % depth of discharge in the Zn symmetric cell. The designing principles and mechanism analysis in this study could serve as a source of inspiration in exploring novel additives for advanced Zn anodes.

A Bio-Inspired Trehalose Additive for Reversible Zinc Anodes with Improved Stability and Kinetics.

The moderate reversibility of Zn anodes, as a long-standing challenge in aqueous zinc-ion batteries, promotes the exploration of suitable electrolyte additives continuously. It is crucial to establish the absolute predominance of smooth deposition within multiple interfacial reactions for stable zinc anodes, including suppressing side parasitic reactions and facilitating Zn plating process. Trehalose catches our attention due to the reported mechanisms in sustaining biological stabilization. In this work, the inter-disciplinary application of trehalose is reported in the electrolyte modification for the first time. The pivotal roles of trehalose in suppressed hydrogen evolution and accelerated Zn deposition have been investigated based on the principles of thermodynamics as well as reaction kinetics. The electrodeposit changes from random accumulation of flakes to dense bulk with (002)-plane exposure due to the unlocked crystal-face oriented deposition with trehalose addition. As a result, the highly reversible Zn anode is obtained, exhibiting a high average CE of 99.8 % in the Zn/Cu cell and stable cycling over 1500 h under 9.0 % depth of discharge in the Zn symmetric cell. The designing principles and mechanism analysis in this study could serve as a source of inspiration in exploring novel additives for advanced Zn anodes.

Preferred Orientation Deposition via Multifunctional Gel Electrolyte with Molecular Anchor Enabling Highly Reversible Zn Anode.

The high activity of water molecules results in a series of awful parasitic reaction, which seriously impede the development of aqueous zinc batteries. Herein, a new gel electrolyte with multiple molecular anchors is designed by employing natural biomaterials from chitosan and chlorophyll derivative. The gel electrolyte firmly anchors water molecules by ternary hydrogen bonding to reduce the activity of water molecules and inhibit hydrogen evolution reaction. Meanwhile, the multipolar charged functional groups realize the gradient induction and redistribution of Zn2+ , which drives oriented Zn (002) plane deposition of Zn2+ and then achieves uniform Zn deposition and dendrite-free anode. As a result, it endows the Zn||Zn cell with over 1700h stripping/plating processes and a high efficiency of 99.4% for the Zn||Cu cell. In addition, the Zn||V2 O5 full cells also exhibit capacity retention of 81.7% after 600 cycles at 0.5 A g-1 and excellent long-term stability over 1600 cycles at 2 A g-1 , and the flexible pouch cells can provide stable power for light-emitting diodeseven after repeated bending. The gel electrolyte strategy provides a reference for reversible zinc anode and flexible wearable devices.

Dual Electrolyte Additives Enabling Bilayer SEI to Suppress Hydrogen Evolution Reaction in Aqueous Li-Ion Batteries

Aqueous Li-ion batteries (LIBs) feature safe operation, low cost, and environmental friendliness, but suffer from low energy density due to narrow electrochemical stability window (ESW) of aqueous electrolytes. While exploiting high-salt-concentration strategy of water-in-salt electrolytes (WiSEs) is effective in improving the electrochemical stability, the improvement is still insufficient to ensure practical feasibility of aqueous LIBs. In particular, the reduction stability of WiSEs needs further improvement to enable stable operation of low-voltage anode materials including Li4Ti5O12.This talk reports that the co-use of two electrolyte additives can effectively expand the cathodic limit of various WiSE systems. The synergistic effect between the two additives is attributed to the formation of unique solid-electrolyte interphase composed of organic and inorganic bilayers. The inner inorganic layer suppresses hydrogen evolution reaction, while the outer hydrophobic organic polymer mitigates the dissolution of inner SEI. LiMn2O4/Li4Ti5O12 cells employing 21 m LiTFSI WISE with the dual additives exhibit excellent long-term cycling (>70% retention after 400 cycles at 25 oC) and good rate capability (110 mAh/g at 6 mA/cm2). The efficacy of the dual-additive approach is also demonstrated for other WiSE solutions including water-in-bisalt, hydrate melt, and aqueous/organic hybrid electrolytes, suggesting the general applicability of the dual-additive strategy. Figure 1

Pressure-Electrochemistry as a Pathway to Novel Metal Hydrides

We have developed a pressure-electrochemical cell apparatus to electrochemically insert hydrogen into metals at applied pressures of 1GPa. The coupling of pressure and potential (P^2) was motivated by our recent density functional theory calculations that predicted the stability of novel metal hydride phases when both pressure and potential are applied [1]. In this work, we adapted a traditional piston-cylinder pressure apparatus into a pressure-electrochemical cell by replacing the inert pressure transmitting medium with a proton-conducting liquid electrolyte (1M NaOH + polyvinyl alcohol) such that it not only provides hydrostatic pressure but also reduces into hydrogen, which is then absorbed into the metal cathode. The pressure being applied by the electrolyte was verified by measuring an increase in the electrical resistance of manganin alloy with pressure. We then electrochemically hydrogenated yttrium foil under varying pressures ranging from 0.25 to 1GPa, measuring the extent of hydrogenation post-mortem using x-ray diffraction. We find that the application of pressure suppresses hydrogen evolution, improving the current efficiency of hydrogenation of Y into YH3 from 45% at 0.25GPa to 75% at 1GPa. The development of the pressure-electrochemical apparatus unlocks a new pathway in potentially synthesizing novel metal hydrides.[1] P.-W. Guan, R. J. Hemley, V. Viswanathan, Proceedings of the National Academy of Sciences. 118, e2110470118 (2021).

Simultaneous Boosting Nitrogen Reduction Activity and Suppressing Hydrogen Evolution Reaction Activity of Transition Metal Oxide Based Electrocatalyst

Ammonia (NH3) is widely served as fertilizer, safer chemical hydrogen storage, and energy conservation materials with an annual production around 200 million tons per year. Currently, NH3 is mainly synthesized via the Haber-Bosch process, which is an extremely energy- and capital-intensive (high temperature 400–500 °C and high pressure 100–350 atm) process, consuming over 1% of the global annual energy output, emitting massive amount of greenhouse gases (~420 Mt CO2 annually), and causing serious concerns with climate change. Electrochemical nitrogen reduction reaction (eNRR) allows NH3 production from nitrogen (N2) and water (H2O) under ambient conditions. Especially if driven by renewable energies, NRR represents a potentially clean and sustainable strategy for replacing the traditional Haber-Bosch process and alleviating climate change effect. One of the most critical fundamental challenges in production of ammonia via electrochemical nitrogen reduction reaction (eNNR) is developing catalysts which are capable to boost eNRR activity and concurrently suppress the overwhelming competitive hydrogen evolution reaction (HER). This work reports a new strategy to develop such catalysts to alleviate this challenge. This new strategy for the first time takes advantage of the outstanding capability of some redox active transition metal oxides (TMOs) in their super capability in electrochemically controlled proton interstitial doping and the associated remarkable structural changes to boost their NRR activity. Further, inspired by their unique hydrogen intercalation determined HER activity, this new strategy introduced cationic substitutional doping of the TMOs with nonmetal elements, such as phosphorus (P), to modulate their proton intercalation behavior, achieving HER suppression. In this work, tungsten oxide nanosheets (WO3) have been exploited as a typical example of such TMOs to demonstrate the feasibility of this innovative strategy. It is found that cationic P doping also accompanies introduction of large quantity of oxygen vacancies (OVs) in the matrix of the WO3 and structural changes of the WO3 lattice. The synergy of the substitutional doping and interstitial doping in tuning the electronic and the local geometric structures leads to significantly enhanced eNNR performance of WO3 nanosheets. An unprecedented high Faradaic efficiency (FE) of 64.1% with NH3 yield of 24.5 µg h-1 has been reached, representing the highest NRR performance for WO3 based catalysts. It is worth mentioning that the P-doped WO3 catalyst (200 nm square with a thickness of 20-40 nm) is much larger than most of the reported catalyst. The catalytic yield is even higher than that achieved with atomic thin two-dimensional (2D) WO3 nanosheets (OV-rich) catalysts (17 µg h-1 with a FE of 7.0%), which is known for their high catalytic efficiency due to the excellent accessibility of all the catalytic active sites. It is also worthwhile to mention that the FE of 64.1% is comparable to that of the natural nitrogenase can be reached (65%), which is unprecedented high compared to most of catalysts reported so far (<25%). In addition, inclusion of Li ions in the electrolyte further increased the NH3 yield to 60.1 µg h-1 with the high FE largely remained, reached the highest eNNR performance for all the TMO based catalysts. Density functional theory calculations further revealed the synergistic role of interstitial doping of H* and substitutional cationic doping of P, and the associated generation of OVs in increasing the electronic states crossing the Fermi level of the WO3 and thus reducing reaction energy barrier in N2 activation and hydrogenation. An interesting non-PCET (proton coupled electron transfer) mechanism is revealed in the first step and the rate determining step during eNNR, providing a new design principle for TMO-based catalysts. Figure 1

Tailoring Microenvironment in Bilayer Electrode with Copper and Silver Nanocatalysts for Bicarbonate Electroreduction to Multicarbon Products

As compared with CO2 electrolyzers, bicarbonate electrolyzers can achieve direct conversion of CO2 captured solutions to higher-valued chemicals, that can bypass energy-intensive steps of CO2 regeneration and pressurization processes. However, most previous studies have only reported single carbon chemicals (i.e., CO, formate, CH4) as the major products so far. In this presentation, we will present direct electro-reduction of potassium bicarbonate (KHCO3) to multicarbon (C2+) products (i.e., acetate, ethylene, ethanol, propanol) using rationally designed bilayer of Cu and Ag nanosized catalysts. The in-situ generated CO2 was first reduced to CO on the Ag layer, followed by CO reduction to C2+ products on the Cu layer benefiting from locally high concentration of CO. Through optimizing the configurations, compositions, ionomer types, and local hydrophobicity of the bilayer electrode, we have created the favorable microenvironment (high local pH, low water content, etc.) to increase bicarbonate conversion to C2+ products with a largely suppressed hydrogen evolution reaction, and a remarkable C2+ FE of 41.6% at a current density of 100 mA cm−2 was achieved.

Manipulating cation-water chemistry to inhibit hydrogen evolution of zinc metal anodes

The electrochemical behavior of zinc metal anodes is dominated by the interfacial chemistry between the anode and the electrolyte. The local enrichment of cation-solvent complexes with strong interactions in the Helmholtz plane can lead to the evolution of hydrogen on the Zn anode surface during cycling. To tackle this issue, we propose the addition of low doses of N-dimethylformamide (DMF) solvent into 2 M of ZnSO4 electrolyte (D-ZS) to inhibit hydrogen evolution from water splitting and dendrite growth. Molecular dynamics simulation and nuclear magnetic resonance spectroscopy reveal that high donor-number DMF molecules replace part of H2O molecules, thereby reducing the amount of H2O in the solvated sheath of Zn2+. Furthermore, density functional theory calculations demonstrate that DMF increases the lowest unoccupied molecular orbital level of bound water owing to reduced Zn2+ cation-water interaction, preventing the breakage of O−H bond and reducing side reactions of Zn anodes. In addition, the desolvated DMF molecules prefer to adsorb on the zinc anode surface, hindering the migration of Zn2+ to low surface-energy positions that could lead to dendritic formation. As a result, a symmetric cell with D-ZS electrolyte can operate for over 1970 h at 0.5 mA cm−2 for 0.25 mAh cm−2, and Zn-ion hybrid supercapacitors achieve an exemplary cycle performance (93% of capacity retention rate after 30,000 cycles at 2 A g−11). The present work provides a roadmap for regulating electrolyte structure to inhibit hydrogen evolution of zinc metal anodes by manipulating Zn2+ cation-water chemistry.

Pulse cyclone electrowinning of gallium recovery for higher current efficiency and lower energy consumption

Traditional gallium electrowinning suffers from low current efficiency and high specific energy consumption due to the inevitable hydrogen evolution reaction. In order to inhibit hydrogen evolution reaction and alleviate the concentration polarization, the pulse cyclone electrowinning process was proposed and developed to enhance diffusion and convection. During the pulse current off time, the ion concentration in the cathode diffusion layer can be effectively restored, while forced convection accelerates this process. Electrochemical experiments using a rotating disk electrode have preliminarily confirmed that pulsed electrodeposition can accelerate nucleation and improve current efficiency. Pilot experiments were conducted using an industrial gallium electrolyte to further validate the feasibility of the pulse cyclone electrowinning process. Under the following conditions: current density of 2000 A/m2, duty ratio of 50%, frequency of 10 Hz, and circulation flow of 400 L/h, the current efficiency and specific energy consumption were determined to be 69.21% and 7836 kWh/t, respectively. Compared to the traditional electrowinning process at the same average current density, pulse cyclone electrowinning exhibited a significant increase in current efficiency and a reduction in specific energy consumption by 52.28% and 31.57%, respectively. Overall, this study confirmed the feasibility of pulse cyclone electrowinning coupling pulse current and forced convection, which can also be applied to other electrodeposition processes to achieve higher current efficiency and lower energy consumption.

Boosting uniform nucleation and suppressing hydrogen evolution with an in-situ formed zinc hyaluronate protective film on zinc anodes

Developing long-cycle stable Zn-ion batteries encounters significant challenges associated with Zn anodes. To address these issues, we propose an interface engineering strategy using an artificial protective layer called zinc hyaluronate (ZH) on the Zn anode surface. The ZH film acts as a barrier, preventing direct contact between Zn anode and electrolyte, reducing hydrogen evolution and corrosion. Its carboxyl and hydroxyl groups create uniform and plentiful nucleophilic sites for Zn2+ ions, promoting uniform Zn deposition and suppressing dendrite growth. Remarkably, a Zn//Zn symmetric cell assembled with ZH-decorated Zn foil (Zn@ZH) exhibits outstanding cycle life, lasting 3600 h at a current density of 5 mA cm−2 and a capacity density of 5 mAh cm−2, much better than cells with pristine Zn anode. Even under extremely tough conditions of 10 mA cm−2 and 10 mAh cm−2, the battery life exceeds 1300 h. Furthermore, the Zn@ZH//V2O5 full cell demonstrates superior capacity retention compared to the Zn//V2O5 cell after 1000 cycles at a current density of 10 A g−1. These results highlight the benefits of the artificial protective layer strategy for advanced Zn anodes, providing insights into the underlying mechanism and promoting the development of high-performance aqueous zinc ion batteries.

Molecular Engineering of Cation Solvation Structure for Highly Selective Carbon Dioxide Electroreduction.

Balancing the activation of H2O is crucial for highly selective CO2 electroreduction (CO2RR), as the protonation steps of CO2RR require fast H2O dissociation kinetics, while suppressing hydrogen evolution (HER) demands slow H2O reduction. We herein proposed one molecular engineering strategy to regulate the H2O activation using aprotic organic small molecules with high Gutmann donor number as a solvation shell regulator. These organic molecules occupy the first solvation shell of K+ and accumulates in the electrical double layer, decreasing the H2O density at the interface and the relative content of proton suppliers (free and coordinated H2O), suppressing the HER. The adsorbed H2O was stabilized via second sphere effect and its dissociation was promoted by weakening the O-H bond, which accelerates the subsequent *CO2 protonation kinetics and reduces the energy barrier from 0.93 to 0.42 eV. In the model electrolyte containing 5 M dimethyl sulfoxide (DMSO) as an additive (KCl-DMSO-5), the highest CO selectivity over Ag foil increased to 99.2%, with FECO higher than 90.0% within -0.75 to -1.15 V (vs. RHE). This molecular engineering strategy for cation solvation shell can be extended to other metal electrodes, such as Zn and Sn, and organic molecule like N,N-dimethylformamide.

Molecular Engineering of Cation Solvation Structure for Highly Selective Carbon Dioxide Electroreduction

AbstractBalancing the activation of H2O is crucial for highly selective CO2 electroreduction (CO2RR), as the protonation steps of CO2RR require fast H2O dissociation kinetics, while suppressing hydrogen evolution (HER) demands slow H2O reduction. We herein proposed one molecular engineering strategy to regulate the H2O activation using aprotic organic small molecules with high Gutmann donor number as a solvation shell regulator. These organic molecules occupy the first solvation shell of K+ and accumulate in the electrical double layer, decreasing the H2O density at the interface and the relative content of proton suppliers (free and coordinated H2O), suppressing the HER. The adsorbed H2O was stabilized via the second sphere effect and its dissociation was promoted by weakening the O−H bond, which accelerates the subsequent *CO2 protonation kinetics and reduces the energy barrier. In the model electrolyte containing 5 M dimethyl sulfoxide (DMSO) as an additive (KCl‐DMSO‐5), the highest CO selectivity over Ag foil increased to 99.2 %, with FECO higher than 90.0 % within −0.75 to −1.15 V (vs. RHE). This molecular engineering strategy for cation solvation shell can be extended to other metal electrodes, such as Zn and Sn, and organic molecules like N,N‐dimethylformamide.