Superwetting Electrodes for Gas-Involving Electrocatalysis

Gas-involving electrochemical reactions, including gas evolution reactions and gas consumption reactions, are essential components of the energy conversion processes and gathering elevating attention from researchers. Besides the development of highly active catalysts, gas management during gas-involving electrochemical reactions is equally critical for industrial applications to achieve high reaction rates (hundreds of milliamperes per square centimeter) under practical operation voltages. Biomimetic surfaces, which generally show regular micro/nanostructures, offer new insights to address this issue because of their special wetting capabilities. Although a series of nanoarray-based structured electrodes have been constructed and demonstrated with excellent performances for gas-involving electrochemical reactions, understanding of bubble wetting behavior remains elusive. In this Account, our recent works including understanding the way to achieve the superwetting properties of solid electrode surfaces, and our advanced design and fabrication of superwetting electrodes for different types of electrochemical gas-involving electrochemical reactions are summarized. To begin, we first put forward several criteria of superwetting surfaces, including superaerophobic surfaces and superaerophilic surfaces. Then, we discuss how the nanoarray-based surface engineering technology can achieve the superwetting properties, in which high roughness of the nanoarray architecture is discovered to be a critical factor for constructing superaerophobic and superaerophilic surfaces. Finally, the feasibility of superwetting electrodes for enhancing the performances of gas-involving electrochemical reactions is also analyzed. Based on theoretical guidance, a series of superaerophobic and superaerophilic electrodes with various methods, such as hydrothermal reactions, electrodeposition technology and high-temperature vapor phase growth, have been built for practice. By comparing with the traditional planar electrodes fabricated by drop-casting method, the superaerophobic electrodes afford a low adhesion force to gas products and accelerate gas bubbles evolution, resulting in fast current increase and stable current for gas evolution reactions. This phenomenon is confirmed by operating different gas evolution reactions (hydrogen evolution, oxygen evolution and hydrazine oxidation) using superaerophobic electrodes with different catalysts (e.g., MoS₂, Pt and Cu). On the other side, the superaerophilic electrodes can improve the catalytic performance of gas consumption reaction (e.g., oxygen reduction reaction) by facilitating gas diffusion and electron transport. Following theoretical analyses and experimental demonstrations, we assemble several energy conversion systems (e.g., electrochemical water splitting and direct hydrazine fuel cells) based on superwetting electrodes and test their performances. By virtue of the structural advantages of electrodes, these energy conversion systems show much higher energy efficiencies than their counterparts. In the last section, we put forward several future fields which are worthy for further exploration as rational extensions of the superwetting electrodes.