Insight into Electrochemical CO₂ Reduction on Surface-Molecule-Mediated Ag Nanoparticles

The electrochemical CO₂ reduction reaction to form valued hydrocarbon molecules is an attractive process, because it can be coupled with renewable energy resources for carbon recycling. For an efficient CO₂ conversion, designing a catalyst with high activity and selectivity is crucial, because the CO₂ reduction reaction in aqueous media competes with the hydrogen evolution reaction (HER) intensely. We have developed a strategy to tune CO₂ reduction activity by modulating the binding energies of the intermediates on the electrocatalyst surfaces with the assistance of molecules that contain the functional group. We discovered that the amine functional group on Ag nanoparticle is highly effective in improving selective CO production (Faradaic efficiency to 94.2%) by selectively suppressing HER, while the thiol group rather increases HER activity. A density functional theory (DFT) calculation supports the theory that attaching amine molecules to Ag nanoparticles destabilizes the hydrogen binding, which effectively suppresses HER selectively, while an opposite tendency is found with thiol molecules. In addition, changes in the product selectivity, depending on the functional group, are also observed when the organic molecules are added after nanoparticle synthesis or nanoparticles are immobilized with an amine (or thiol)-containing anchoring agent. CO Faradaic efficiencies were consistently improved when the Ag nanoparticle was modified with amine groups, compared with that of its thiol counterpart

Simple Chemical Solution Deposition of Co₃O₄ Thin Film Electrocatalyst for Oxygen Evolution Reaction

Oxygen evolution reaction (OER) is the key reaction in electrochemical processes, such as water splitting, metal–air batteries, and solar fuel production. Herein, we developed a facile chemical solution deposition method to prepare a highly active Co₃O₄ thin film electrode for OER, showing a low overpotential of 377 mV at 10 mA/cm² with good stability. An optimal loading of ethyl cellulose additive in a precursor solution was found to be essential for the morphology control and thus its electrocatalytic activity. Our results also show that the distribution of Co₃O₄ nanoparticle catalysts on the substrate is crucial in enhancing the inherent OER catalytic performance

Selective CO₂ Reduction on Zinc Electrocatalyst: The Effect of Zinc Oxidation State Induced by Pretreatment Environment

Here, we have developed porous nanostructured Zn electrocatalysts for CO₂ reduction reaction (CO₂RR), fabricated by reducing electrodeposited ZnO (RE-Zn) to activate the CO₂RR electrocatalytic performance. We discovered that the electrochemical activation environment using CO₂-bubbled electrolyte during reducing ZnO in a pretreatment step is important for highly selective CO production over H₂ production, while using Ar gas bubbling instead can lead to less CO product of the Zn-based catalyst in CO₂RR later. The RE-Zn activated in CO₂-bubbled electrolyte condition achieves a Faradaic efficiency of CO production (FE_CO) of 78.5%, which is about 10% higher than that of RE-Zn activated in Ar-bubbled electrolyte. The partial current density of CO product had more 10-fold increase with RE-Zn electrodes than that of bulk Zn foil at −0.95 V vs RHE in KHCO₃. In addition, a very high FE_CO of 95.3% can be reached using the CO₂-pretreated catalyst in KCl electrolyte. The higher amount of oxidized zinc states has been found in the high performing Zn electrode surface by high-resolution X-ray photoelectron spectroscopy studies, which suggest that oxidized zinc states induce the active sites for electrochemical CO₂RR. Additionally, in pre- and post-CO₂RR performance tests, the carbon deposition is also significantly suppressed on RE-Zn surfaces having a higher ratio of oxidized Zn state

Sloughing a Precursor Layer to Expose Active Stainless Steel Catalyst for Water Oxidation

Hydrogen production by water electrolysis has been regarded as a promising approach to wean away from sourcing energy through fossil fuels, as the produced hydrogen gas can be converted to electrical or thermal energy without any harmful byproducts. However, an efficient hydrogen production is restricted by the sluggish oxygen evolution reaction (OER) at the counter anode. Therefore, the development of new OER catalysts with high catalytic activities is crucial for high performance water splitting. Here, we report a novel sloughing method for the fabrication of an efficient OER catalyst on a stainless steel (SS) surface. A chalcogenide (Fe–S) overlayer generated by sulfurization on the SS surface is found to play a critical role as a precursor layer in the formation of an active surface during water oxidation. Interestingly, a newly exposed catalytic layer after sloughing off the Fe–S overlayer has a nanoporous structure with changed elemental composition, resulting in a significant improvement in OER performance with an overpotential value of 267 mV at a current density of 10 mA cm^–2 (in 1 M KOH). Our novel method for the preparation of OER catalyst provides an important insight into designing an efficient and stable electrocatalyst for the water splitting community