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

Abstract

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.

Microscale Contacts for Nanowire Characterization Using Microscope Projection Photolithography

“…Microscope projection photolithography is a versatile and cost-effective method of transferring a pattern to a small substrate (e.g., <1 cm 2 ). This technique can be used to produce patterns without the need for equipment, such as mask aligners, or the need for a clean room environment, since MPP is accomplished without physical contact with the surfaces of a substrate. , As such, MPP is an ideal technique for rapid prototyping in a variety of applications, such as in microfluidics, , microelectromechanical systems, textured electrocatalysts, integrated circuits, and micro-to-nanoscale optical components. , A variety of systems have been reported to demonstrate reliable, low-cost fabrication of micro-to-nanoscale structures using MPP. These MPP systems have included (i) the use of colored masks to create multilevel structures; (ii) the use of ultraviolet light-emitting diodes (UV-LEDs) as the light source for the fabrication of components, such as nanoscale optical devices; , and (iii) numerous designs for maskless MPP systems, such as those that use liquid crystal displays or digital micromirror devices in place of a mask or focused electron-beam writing techniques. − …”