# Rational Strain Engineering in Delafossite Oxides for Highly Efficient Hydrogen Evolution Catalysis in Acidic Media

## TL;DR

This paper introduces a new family of delafossite oxide electrocatalysts for hydrogen evolution in acid, demonstrating that strain-engineered surface modifications significantly enhance catalytic activity beyond platinum.

## Contribution

It presents the design and synthesis of strain-stabilized delafossite-based catalysts, revealing how in-situ surface modifications improve HER performance in acidic media.

## Key findings

- PdCoO₂ shows increased exchange current density and reduced Tafel slope.
- Surface modification stabilizes β-palladium hydride phase.
- Overpotentials below 15 mV at 10 mA/cm².

## Abstract

The rational design of hydrogen evolution reaction (HER) electrocatalysts which are competitive with platinum is an outstanding challenge to make power-to-gas technologies economically viable. Here, we introduce the delafossites PdCrO$_2$, PdCoO$_2$ and PtCoO$_2$ as a new family of electrocatalysts for the HER in acidic media. We show that in PdCoO$_2$ the inherently strained Pd metal sublattice acts as a pseudomorphic template for the growth of a strained (by +2.3%) Pd rich capping layer under reductive conditions. The surface modification continuously improves the electrocatalytic activity by simultaneously increasing the exchange current density j$_0$ from 2 to 5 mA/cm$^2_{geo}$ and by reducing the Tafel slope down to 38 mV/decade, leading to overpotentials $\eta_{10}$ < 15 mV for 10 mA/cm$^2_{geo}$, superior to bulk platinum. The greatly improved activity is attributed to the in-situ stabilization of a $\beta$-palladium hydride phase with drastically enhanced surface catalytic properties with respect to pure or nanostructured palladium. These findings illustrate how operando induced electrodissolution can be used as a top-down design concept for rational surface and property engineering through the strain-stabilized formation of catalytically active phases.

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Source: https://tomesphere.com/paper/1903.10576