Enhancing the Performance of Nickel Electrocatalysts for the Oxygen Evolution Reaction Using Arrays of Self-Cleaning Linear Ridges

The oxygen evolution reaction represents a key source of inefficiency for green hydrogen production. In general, persistent bubbles that grow on the surfaces of an electrode obstruct a portion of the electrochemically active surface area, resulting in a decreased overall efficiency. Microscale features on the surfaces of electrocatalysts can, however, aid in the removal of these adherent bubbles. Gas production and conversion efficiencies have been shown to improve when incorporating linear, ridge-like microscale features onto electrodes. These factors improve with an increase in the separation between these ridges as demonstrated for features with separations up to 200 μm, but the full extent of this trend is not known. In this study, a series of linear, ridge-like features were prepared to seek a separation between these features that yields an optimal performance. The ridge-like features were prepared from nickel (Ni) using microscope project lithography techniques in combination with Ni electrodeposition, which was demonstrated to be a versatile technique for rapidly prototyping these features. At an industrially relevant potential of 1.8 V vs mercury/mercury oxide (Hg/HgO) in an alkaline electrolyte, the performance of arrays of the ridge-like features was observed to increase up to a critical separation of ∼300 μm, beyond which the performance decreased and approached that of planar Ni electrocatalysts. At this identified critical separation of features, the current response under chronoamperometry conditions was nearly triple that obtained for the planar Ni electrocatalysts. Observations of growth, coalescence, and detachment of gas bubbles on the microscale ridge-like features achieved using high-speed imaging suggest a possible cause for the improved performance at the identified optimal spacing of the arrays of linear features.