Combining Nanoconfinement in Ag Core/Porous Cu Shell Nanoparticles with Gas Diffusion Electrodes for Improved Electrocatalytic Carbon Dioxide Reduction

Ag-Co3 O4 -CoOOH-Nanowires Tandem Catalyst for Efficient Electrocatalytic Conversion of Nitrate to Ammonia at Low Overpotential via Triple Reactions

The electrocatalytic conversion of nitrate (NO3 ‾) to NH3  (NO3 RR) offers a promising alternative to the Haber-Bosch process. However, the overall kinetic rate of NO3 RR is plagued by the complex proton-assisted multiple-electron transfer process. Herein, Ag/Co3 O4 /CoOOH nanowires (i-Ag/Co3 O4  NWs) tandem catalyst is designed to optimize the kinetic rate of intermediate reaction for NO3 RR simultaneously. The authors proved that NO3 ‾ ions are reduced to NO2 ‾ preferentially on Ag phases and then NO2 ‾ to NO on Co3 O4  phases. The CoOOH phases catalyze NO reduction to NH3  via NH2 OH intermediate. This unique catalyst efficiently converts NO3 ‾ to NH3  through a triple reaction with a high Faradaic efficiency (FE) of 94.3% and a high NH3  yield rate of 253.7 μmol h-1  cm-2  in 1 M KOH and 0.1 M KNO3  solution at -0.25 V versus RHE. The kinetic studies demonstrate that converting NH2 OH into NH3  is the rate-determining step (RDS) with an energy barrier of 0.151 eV over i-Ag/Co3 O4  NWs. Further applying i-Ag/Co3 O4  NWs as the cathode material, a novel Zn-nitrate battery exhibits a power density of 2.56 mW cm-2  and an FE of 91.4% for NH3  production.

Multilayer-Cavity Tandem Catalyst for Profiling Sequentially Coupling of Intermediate CO in Electrocatalytic Reduction Reaction of CO2 to Multi-Carbon Products

Electrochemical CO2  reduction reaction (CO2 RR) is an effective approach to address CO2  emission, promote recycling, and synthesize high-value multi-carbon (C2+ ) chemicals for storing renewable electricity in the long-term. The construction of multilayer-bound nanoreactors to achieve management of intermediate CO is a promising strategy for tandem to C2+ products. In this study, a series of Ag@Cu2 O nanoreactors consisting of an Ag-yolk and a multilayer confined Cu shell is designed to profile electrocatalytic CO2 RR reactions. The optimized Ag@Cu2 O-2 nanoreactor exhibits a 74% Faradaic efficiency during the C2+ pathway and remains stable for over 10 h at a bias current density of 100 mA cm-2 . Using the finite element method, this model determines that the certain volume of cavity in the Ag@Cu2 O nanoreactors facilitates on-site CO retention and that multilayers of Cu species favor CO capture. Density functional theory calculations illustrate that the biased generation of ethanol products may arise from the (100)/(111) interface of the Cu layer. In-depth explorations in multilayer-bound nanoreactors provide structural and interfacial guidance for sequential coupling of CO2 RR intermediates for efficient C2+ generation.

Bridging Trans-Scale Electrode Engineering for Mass CO2 Electrolysis

Electrochemical CO2 upgrade offers an artificial route for carbon recycling and neutralization, while its widespread implementation relies heavily on the simultaneous enhancement of mass transfer and reaction kinetics to achieve industrial conversion rates. Nevertheless, such a multiscale challenge calls for trans-scale electrode engineering. Herein, three scales are highlighted to disclose the key factors of CO2 electrolysis, including triple-phase boundaries, reaction microenvironment, and catalytic surface coordination. Furthermore, the advanced types of electrolyzers with various electrode design strategies are surveyed and compared to guide the system architectures for continuous conversion. We further offer an outlook on challenges and opportunities for the grand-scale application of CO2 electrolysis. Hence, this comprehensive Perspective bridges the gaps between electrode research and CO2 electrolysis practices. It contributes to facilitating the mixed reaction and mass transfer process, ultimately enabling the on-site recycling of CO2 emissions from industrial plants and achieving net negative emissions.

Simultaneous Anodic and Cathodic Formate Production in a Paired Electrolyzer by CO2 Reduction and Glycerol Oxidation

Electrochemical CO₂ conversion is a key technology to promote the production of carbon-containing molecules, alongside reducing CO₂ emissions leading to a closed carbon cycle economy. Over the past decade, the interest to develop selective and active electrochemical devices for electrochemical CO₂ reduction emerged. However, most reports employ oxygen evolution reaction as an anodic half-cell reaction causing the system to suffer from sluggish kinetics with no production of value-added chemicals. Therefore, this study reports a conceptualized paired electrolyzer for simultaneous anodic and cathodic formate production at high currents. To achieve this, CO₂ reduction was coupled with glycerol oxidation: a BiOBr-modified gas-diffusion cathode and a Ni_x B on Ni foam anode keep their selectivity for formate in the paired electrolyzer compared to the half-cell measurements. The paired reactor here reaches a combined Faradaic efficiency for formate of 141 % (45 % anode and 96 % cathode) at a current density of 200 mA cm^-2 .

Operando Scanning Electrochemical Probe Microscopy during Electrocatalysis

Scanning electrochemical probe microscopy (SEPM) techniques can disclose the local electrochemical reactivity of interfaces in single-entity and sub-entity studies. Operando SEPM measurements consist of using a SEPM tip to investigate the performance of electrocatalysts, while the reactivity of the interface is simultaneously modulated. This powerful combination can correlate electrochemical activity with changes in surface properties, e.g., topography and structure, as well as provide insight into reaction mechanisms. The focus of this review is to reveal the recent progress in local SEPM measurements of the catalytic activity of a surface toward the reduction and evolution of O₂ and H₂ and electrochemical conversion of CO₂. The capabilities of SEPMs are showcased, and the possibility of coupling other techniques to SEPMs is presented. Emphasis is given to scanning electrochemical microscopy (SECM), scanning ion conductance microscopy (SICM), electrochemical scanning tunneling microscopy (EC-STM), and scanning electrochemical cell microscopy (SECCM).

Single-entity Electrochemistry Unveils Dynamic Transformation during Tandem Catalysis of Cu2 O and Co3 O4 for Converting NO3 - to NH3

Electrochemically converting nitrate to ammonia is an essential and sustainable approach to restoring the globally perturbed nitrogen cycle. The rational design of catalysts for the nitrate reduction reaction (NO₃ RR) based on a detailed understanding of the reaction mechanism is of high significance. We report a Cu₂ O+Co₃ O₄ tandem catalyst which enhances the NH₃ production rate by ≈2.7-fold compared to Co₃ O₄ and ≈7.5-fold compared with Cu₂ O, respectively, however, most importantly, we precisely place single Cu₂ O and Co₃ O₄ cube-shaped nanoparticles individually and together on carbon nanoelectrodes provide insight into the mechanism of the tandem catalysis. The structural and phase evolution of the individual Cu₂ O+Co₃ O₄ nanocubes during NO₃ RR is unveiled using identical location transmission electron microscopy. Combining single-entity electrochemistry with precise nano-placement sheds light on the dynamic transformation of single catalyst particles during tandem catalysis in a direct way.

Selective and high-rate CO2 electroreduction by metal-doped covalent triazine frameworks: a computational and experimental hybrid approach

The electrochemical CO₂ reduction reaction (CO₂RR) has attracted intensive attention as a technology to achieve a carbon-neutral society. The use of gas diffusion electrodes (GDEs) enables the realization of high-rate CO₂RRs, which is one of the critical requirements for social implementation. Although both a high reaction rate and good selectivity are simultaneously required for electrocatalysts on GDEs, no systematic study of the relationship among active metal centers in electrocatalysts, reaction rate, and selectivity under high-rate CO₂RR conditions has been reported. In the present study, we employed various metal-doped covalent triazine frameworks (M-CTFs) as platforms for CO₂ reduction reaction (CO₂RR) electrocatalysts on GDEs and systematically investigated them to deduce sophisticated design principles using a combined computational and experimental approach. The Ni-CTF showed both high selectivity (faradaic efficiency (FE) > 98% at -0.5 to -0.9 V vs. reversible hydrogen electrode) and a high reaction rate (current density < -200 mA cm^-2) for CO production. By contrast, the Sn-CTF exhibited selective formic acid production, and the FE and partial current density reached 85% and 150 mA cm^-2, respectively. These results for the CO₂RR activity and selectivity at high current density with respect to metal centers correspond well with predictions based on first-principles calculations. This work is the first demonstration of a clear relationship between the computational adsorption energy of intermediates depending on metal species and the experimental high-rate gaseous CO₂RR.