# Mechanistic Insights into the Electroreduction of Carbon Dioxide to Formate on Palladium

## TL;DR

This study explores how palladium catalysts convert CO2 to formate and how their structure affects performance and poisoning.

## Contribution

The study reveals how structural features of Pd surfaces influence CO2-to-formate activity and CO poisoning.

## Key findings

- Pd/C shows consistent formate activity due to surface hydride involvement.
- Pd aerogel suffers from CO poisoning due to grain boundaries promoting CO formation.
- Structural optimization of Pd surfaces can enhance formate production efficiency.

## Abstract

The electrochemical reduction of carbon dioxide (or the
CO2-reduction reaction, CO2RR) presents a promising
strategy to mitigate CO2 emissions while producing valuable
chemical feedstocks. Palladium (Pd) catalysts are particularly interesting
for their capacity to selectively produce formate at low overpotentials
and carbon monoxide (CO) at higher overpotentials. However, palladium’s
CO2-to-formate activity is often hindered by the progressive
poisoning of its surface with CO. To shed light on the parameters
that control this performance-determining process, in this study we
employ Operando grazing incidence X-ray absorption spectroscopy and
attenuated total reflectance surface-enhanced infrared absorption
spectroscopy to investigate the CO2RR mechanism on carbon-supported
Pd nanoparticles (Pd/C) and a freestanding Pd aerogel with similar
electrochemical surface areas but substantial differences in hydride
formation, CO poisoning, and catalytic performance. Pd/C demonstrates
rapid hydride formation and constant formate activity at −100
and −200 mV vs the reversible hydrogen electrode, revealing
an indirect correlation between activity for formate and hydride stoichiometry
that strongly indicates the active involvement of the surface hydride
in the CO2RR to formate. In contrast, the Pd aerogel suffers
from rapid CO surface poisoning and a concomitantly negligible formate-production
activity at the same potentials. These differences in catalytic behavior
are linked to an increased presence of grain boundaries in the aerogel’s
surface that has been tied to a reduction in the activation barrier
for CO2 conversion to the surface-adsorbed *COOH and the
subsequent formation of strongly adsorbed CO. As such, our findings
highlight how optimizing the structural features of Pd-based surfaces
can lead to significant enhancements in their efficiency toward formate
production.