Suppression of the Hydrogen Evolution Reaction Is the Key: Selective Electrosynthesis of Formate from CO₂ over Porous In₅₅Cu₄₅ Catalysts

Abstract

Direct electrosynthesis of formate through CO2 electroreduction (denoted CO2RR) is currently attracting great attention because formate is a highly valuable commodity chemical that is already used in a wide range of applications (e.g., formic acid fuel cells, tanning, rubber production, preservatives, and antibacterial agents). Herein, we demonstrate highly selective production of formate through CO2RR from a CO2-saturated aqueous bicarbonate solution using a porous In55Cu45 alloy as the electrocatalyst. This novel high-surface-area material was produced by means of an electrodeposition process utilizing the dynamic hydrogen bubble template approach. Faradaic efficiencies (FEs) of formate production (FEformate) never fell below 90% within a relatively broad potential window of approximately 400 mV, ranging from −0.8 to −1.2 V vs the reversible hydrogen electrode (RHE). A maximum FEformate of 96.8%, corresponding to a partial current density of j formate = −8.9 mA cm–2, was yielded at −1.0 V vs RHE. The experimental findings suggested a CO2RR mechanism involving stabilization of the HCOO* intermediate on the In55Cu45 alloy surface in combination with effective suppression of the parasitic hydrogen evolution reaction. What makes this CO2RR alloy catalyst particularly valuable is its stability against degradation and chemical poisoning. An almost constant formate efficiency of ∼94% was maintained in an extended 30 h electrolysis experiment, whereas pure In film catalysts (the reference benchmark system) showed a pronounced decrease in formate efficiency from 82% to 50% under similar experimental conditions. The identical location scanning electron microscopy approach was applied to demonstrate the structural stability of the applied In55Cu45 alloy foam catalysts at various length scales. We demonstrate that the proposed catalyst concept could be transferred to technically relevant support materials (e.g., carbon cloth gas diffusion electrode) without altering its excellent figures of merit.

Comparative Spectroscopic Study Revealing Why the CO2 Electroreduction Selectivity Switches from CO to HCOO– at Cu–Sn- and Cu–In-Based Catalysts

“…The presence of either In or Sn in the Cu deposition bath is seen to have a significant impact on the nucleation, growth, and break-off rates of the in situ-generated hydrogen bubbles and hence on the fine structure and physical properties (e.g., porosity, thickness, etc.) of the obtained porous foams . The presence of Cu as a foaming agent is essential to create these dendritic microstructures (porous foams) since fabricated pure Sn and In did not show any dendrite-like structures.…”

A comparative spectroscopic study revealing why the CO2 electroreduction selectivity switches from CO to HCOO- at Cu-Sn and Cu-In based catalysts

“…The shape of these electrodeposited dendrites is mainly controlled by the rate of metal deposition and the rate of the concurrent hydrogen evolution reaction. The presence of either In or Sn in the Cu deposition bath is seen to have a significant impact on the nucleation, growth and break-off rates of the in-situ generated hydrogen bubbles, and hence on the f ine structure and physical properties (e.g., porosity, thickness, etc) of the obtained porous foams 21 . The presence of Cu as foaming agent is essential to create these dendritic microstructures (porous f oams), since the f abricated pure Sn and In did not show any dendrite-like structures.…”

Recent progress and prospect of electrodeposition-type catalysts in carbon dioxide reduction utilizations

“…CuAg [17,59] , CuSn [60,61,62,28,63] , CuPb [64] , CuIn [47,65,66] , CuPd [67] , CuBi [68] etc. In Figure 10a, Yeo et al proposed a strategy to compensate for the insufficient CO solubility by introducing Cu x Zn alloy to catalyze the in situ generation of CO during the CO 2 RR process [58] .…”

“…At present, most research studies focus on the combination of Cu with another metal to improve the CDRR performance, such as CuZn, 58 CuAg, 17,59 CuSn, 28,[60][61][62][63] CuPb, 64 CuIn, 47,65,66 CuPd, 67 CuBi, 68 etc. In Fig.…”