Imaging the Footprint of Nanoscale Electrochemical Reactions for Assessing Synergistic Hydrogen Evolution

This work proposes a novel method for measuring the intrinsic activity of single metal‐based nanoparticles towards water reduction in neutral media at industrially relevant current densities. Instead of using gas nanobubbles as proxy, the method uses optical microscopy to track the local footprint of the reaction through the precipitation of metal hydroxide, which is associated to the local pH increase during electrocatalysis. The results show the electrocatalytic activities of different types of metal nanoparticles and bifunctionnal core‐shell nanostructures made of Ni and Pt, and demonstrate the importance of metal hydroxide nano‐shells in enhancing electrocatalysis. This method should be generalizable to any electrocatalytic reaction involving pH changes such as nitrate or CO2 reduction. This study proposes a new optical microscopy technique to measure the synergistic effect of metal hydroxide coatings on the hydrogen evolution reaction at the individual particle level in neutral media. The technique involves using hydroxide halo formation as a footprint of the reaction, and can provide real‐time operando quantification of catalytic activity.