Controlled doping of electrocatalysts through engineering impurities

TL;DR

This paper demonstrates how controlled impurity doping, specifically boron into palladium catalysts, can enhance hydrogen oxidation reaction activity in alkaline fuel cells, enabling cost-effective and stable Pt-free catalysts for energy conversion.

Contribution

It introduces an impurity engineering method to control boron doping in Pd catalysts and explores its effects on HOR activity in alkaline conditions.

Findings

Boron ingress into Pd nano-catalysts can be controlled.

B-doping improves HOR activity in alkaline media.

Ab-initio calculations explain the doping effects.

Abstract

Fuel cells recombine water from H2 and O2 thereby powering e.g. cars or houses with no direct carbon emission. In anion-exchange membrane fuel cells (AEMFCs), to reach high power densities, operating at high pH is an alternative to using large volumes of noble metals catalysts at the cathode, where the oxygen-reduction reaction occurs. However, the sluggish kinetics of the hydrogen-oxidation reaction (HOR) hinders upscaling despite promising catalysts. Here, we observe an unexpected ingress of B into Pd nano-catalysts synthesised by wet-chemistry, gain control over this B-doping, and report on its influence on the HOR activity in alkaline conditions. We rationalize our findings using ab-initio calculations of both H- and OH-adsorption on B-doped Pd. Using this "impurity engineering" approach, we thus design Pt-free catalysts as required in electrochemical energy conversion devices, e.g. next generations of AEMFCs, that satisfy the economic and environmental constraints, i.e. reasonable operating costs and long-term stability, to enable the hydrogen economy.