Optimizing the Performance of Nickel Electrocatalysts with Regular Arrays of Linear Ridge-like Features for Enhancing the Oxygen Evolution Reaction

Abstract

The oxygen evolution reaction (OER) represents a major source of inefficiency in the production of green hydrogen via electrocatalytic water splitting. At high overpotentials relevant to industrial rates of gas production, bubbles can contribute substantially to these inefficiencies by inhibiting the mass transport of electrolyte and partially obstructing the electrochemically active surface area (Aecsa) of an electrode.1 Arrays of microscale features have been shown to improve the efficiency of gas evolving reactions, including the OER. The performance of electrodes modified with linear ridge-like surface features has been previously observed to increase with the spacing between the ridges with a separation of up to 200 µm, but it was not known whether this trend continues indefinitely.2 The present study utilizes rapid prototyping techniques, including microscope projection photolithography and electrodeposition, to determine whether an optimal ridge separation exists between 200 and 450 µm. At a relatively high overpotential of 1.8 V (vs Hg/HgO) in an alkaline electrolyte, the performance of these ridges was observed to increase up to a critical separation, after which the performance decreased to a level comparable to a planar electrode at a wider separation between the ridges. Chronoamperometry measurements indicated that ridges with this optimal spacing attained a current response nearly 3× that of a planar electrode when normalized to (Aecsa). A better understanding of the reasons for this observed trend was pursued using high speed imaging. Direct observations of bubble production on the surfaces of the electrodes provided a deeper understanding of how the distribution of gas bubbles on an electrode affects performance.