# Impact of the Gas Atmosphere at the Triple Boundary Phase on the Measured Oxygen Evolution Reaction Activity of Ni2B/Ni3B Electrocatalysts

## TL;DR

This study shows how the gas environment affects the measurement of oxygen evolution reaction activity in nickel-boron electrocatalysts.

## Contribution

The study reveals that gas convection and composition significantly influence OER activity measurements and that Ni3B has higher activity than Ni2B.

## Key findings

- Gas convection increases measured OER current density compared to no convection.
- CO2 in the atmosphere significantly reduces apparent OER activity.
- Ni3B shows nearly 20% higher OER activity than Ni2B.

## Abstract

The evaluation of the oxygen evolution reaction (OER) electrocatalytic activity of established electrocatalysts is key for the rational design of new electrocatalysts. In this study, scanning electrochemical cell microscopy (SECCM) is employed to assess, under identical conditions, the OER electrocatalytic activity of Ni2B and Ni3B, simultaneously present in a Ni70B30 ingot. An important finding is that the gas environment surrounding the nanodroplet formed at the tip of the SECCM probe and the Ni70B30 ingot impacts the measured current density. The presence of a gas flowing (air, Ar, CO2, and O2) outside the electrolyte droplet increases the measured OER current recorded on both phases, compared to a situation without gas convection, revealing one of the key parameters that can be used to enable higher OER current densities to be recorded on the same catalyst. Notably, the presence of CO2, even in small concentrations (2% O2 in Ar) in the surrounding atmosphere, leads to a significant apparent decrease of the OER activity. The study reveals that Ni3B shows an almost 20% enhanced OER electrocatalytic activity compared to Ni2B, which contradicts previous findings and highlights the importance of precisely controlled experiments enabled by SECCM when establishing catalytic trends.

This study reveals the impact of gas convection and its composition on the oxygen evolution reaction (OER) electrocatalytic activity of Ni‐B catalysts using scanning electrochemical cell microscopy (SECCM). Applying a controlled protective Ar atmosphere, and using a well‐defined Ni‐B specimen, containing Ni3B and Ni2B phases, it is revealed that Ni3B has an increased OER activity compared to Ni2B.