# Interfacial Adsorbate Competition Regulates Intermediate Stabilization and Onset Potential in Acidic CO2 Electroreduction

## TL;DR

This study explores how anions affect CO2 reduction in acidic conditions, showing that sulfate adsorption hinders the process while hydroxyl helps stabilize key reaction steps.

## Contribution

The paper introduces a novel understanding of anion effects on CO2R selectivity and performance in acidic environments using in situ spectroscopy and simulations.

## Key findings

- Sulfate adsorption inhibits CO2R at low pH and delays intermediate formation.
- Hydroxyl coadsorption enables *CO stabilization and supports multicarbon product formation.
- Anion interactions significantly influence CO2R selectivity and overpotentials.

## Abstract

Electrochemical CO2 reduction (CO2R) in acid
may enable high carbon utilization but faces selectivity challenges,
particularly from the Hydrogen Evolution Reaction (HER). While the
source of protons and cation concentrations play a role in this balance,
the role of anions remains underexplored. Here, we combine in situ
surface-enhanced Raman Spectroscopy during CO2R in acid
with theoretical simulations to investigate the role of anionic species
over copper gas diffusion electrodes at application-relevant current
densities (up to 0.2 A·cm–2) and performance.
Our observations reveal that sulfate adsorption inhibits CO2R at low pH and delays CO2R intermediate formation, which
is enabled by hydroxyl species coadsorption. Such competition regulates
*CO stabilization and the balanced *CO coverage needed to favor the
formation of multicarbon products. These results shed light on how
anion interactions govern CO2R selectivity under acidic
conditions and their impact on overpotentials, offering guidance on
catalyst–electrolyte interface design.