Impact of the Gas Atmosphere at the Triple Boundary Phase on the Measured Oxygen Evolution Reaction Activity of Ni ₂ B/Ni ₃ B Electrocatalysts

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.