Exploiting Non-Classical Nucleation for Improved Gas Bubble Mitigation on Nickel Electrocatalysts for the Oxygen Evolution Reaction
Authors: Rea Alex J. G. , Beaurain Janyce , Gates Byron D. 
Published: August 2024

The efficient transport of gas poses a significant challenge in the design of high-performance gas evolving electrocatalysts. Inefficiencies due to mass transport limitations become more pronounced at the high current densities required in industrial electrolyzers, largely as a result of gas bubbles that obstruct a portion of the electrochemically active surface area of the anode and/or cathode, while also hindering electrolyte transport to the electrode surfaces. One promising approach to mitigate these sources of inefficiency is to engineer micro-to-nanoscale surface textures that promote the favorable growth and release of these bubbles. A range of structures have been shown to improve electrocatalyst performance under both stagnant and induced convection conditions, particularly in applications for hydrogen production via electrocatalytic water splitting in alkaline water electrolyzers.1 Trends between surface texture and electrocatalyst performance have been observed for a range of features, such as pillars,2,3 ridges,4 dimples,5 “cracked” structures,6 and electrodeposited crystalline structures,7 however substantial work is still needed to optimize the designs of these materials. These textured surfaces can influence bubble evolution in various ways, such as by altering the wetting properties of a surface, or by providing preferential nucleation sites. Previous studies have noted that surface structures that provide good control over bubble nucleation can often be adversely affected by increased bubble retention.3–5 The present study investigates a method of fabricating patterned electrocatalysts that provides a fine, tunable control over the distribution of bubble nucleation sites on the surfaces of planar Ni electrocatalysts for the oxygen evolution reaction (OER). These textured surfaces are designed to take advantage of so-called “non-classical nucleation” or “type IV nucleation”, a scenario in which gas is trapped at specific surface sites with an effective radius larger than the critical radius for classical nucleation, thereby allowing spontaneous bubble growth without being required to overcome an activation energy barrier.8 The separation between these sites on the surface of the OER active material (i.e., Ni) is then varied to obtain the most favorable distribution of these non-classical nucleation sites. Chronoamperometry is used to compare the current densities achieved by these patterned Ni electrodes to that of a planar Ni electrode. High speed videography is used to directly measure how these textures influence processes such as bubble growth and detachment, and to determine how these processes influence performance. A better understanding of these gas evolution processes can help lower the energy requirements for electrolyzers and may have more general implications for the design of energy efficient gas evolving electrocatalysts relevant to a variety of industrially important reactions.

References:

Angulo, A.; van der Linde, P.; Gardeniers, H.; Modestino, M.; Fernández Rivas, D. Influence of Bubbles on the Energy Conversion Efficiency of Electrochemical Reactors. Joule
2020, 4 (3), 555–579.

Paul, M. T. Y.; Yee, B. B.; Bruce, D. R.; Gates, B. D. Hexagonal Arrays of Cylindrical Nickel Microstructures for Improved Oxygen Evolution Reaction. ACS Appl. Mater. Interfaces
2017, 9 (8), 7036–7043.

Lake, J. R.; Soto, Á. M.; Varanasi, K. K. Impact of Bubbles on Electrochemically Active Surface Area of Microtextured Gas-Evolving Electrodes. Langmuir
2022, 38 (10), 3276–3283.

Taylor, A. K.; Mou, T.; Sonea, A.; Chen, J.; Yee, B. B.; Gates, B. D. Arrays of Microscale Linear Ridges with Self-Cleaning Functionality for the Oxygen Evolution Reaction. ACS Appl. Mater. Interfaces
2021, 13 (2), 2399–2413.

Taylor, A. K.; Andreu, I.; Gates, B. D. Regular Dimpled Nickel Surfaces for Improved Efficiency of the Oxygen Evolution Reaction. ACS Appl. Energy Mater.
2018, 1 (4), 1771–1782.

R. Zeradjanin, A.; A. Topalov, A.; Overmeere, Q. V.; Cherevko, S.; Chen, X.; Ventosa, E.; Schuhmann, W.; J. Mayrhofer, K. J. Rational Design of the Electrode Morphology for Oxygen Evolution – Enhancing the Performance for Catalytic Water Oxidation. RSC Adv.
2014, 4 (19), 9579–9587.

Hyun Ahn, S.; Choi, I.; Park, H. Y.; Jun Hwang, S.; Jong Yoo, S.; Cho, E.; Kim, H. J.; Henkensmeier, D.; Woo Nam, S.; Kim, S. K.; Hyun Jang, J. Effect of Morphology of Electrodeposited Ni Catalysts on the Behavior of Bubbles Generated during the Oxygen Evolution Reaction in Alkaline Water Electrolysis. Chem. Commun.
2013, 49 (81), 9323–9325.

Jones, S. F.; Evans, G. M.; Galvin, K. P. Bubble Nucleation from Gas Cavities — a Review. Adv. Colloid Interface Sci.
1999, 80 (1), 27–50.