Hydrogen is a green and sustainable energy carrier with high energy density and zero carbon emission characteristics. It is an essential part of the sustainable and clean energy system in the future. The integration of renewable energy and water electrolysis to produce "green hydrogen" can achieve zero carbon emission, which is very important for carbon neutralization mission. Acidic water electrolysis with high current density and energy conversion efficiency is important, but its development is restricted by the poor activity and stability of oxygen evolution electrode. Most of the reported catalysts have good performance only at low current density (< 200 mA cm-2), while it is difficult to achieve stable high-current-density (> 200 mA cm-2) operation to meet industrial needs. In addition, under oxidative and corrosive environment, the catalyst is prone to dissolve and fall off from the electrode, worsening its activity and stability and thus limiting its long-term practical use. It is important to develop catalysts that can achieve high current density operation and long-term stability for industrial uses.
Recently, Prof. Bilu LIU and Dr. Qiangmin YU from Tsinghua Shenzhen International Graduate School (Tsinghua SIGS) have published a review paper, discussing recent progress and prospects in improving acidic oxygen evolution reaction (OER) catalysts for practical applications. This review mainly includes intrinsic activity, high current density operation, and long-term stability of catalysts. The researchers propose ways to design and synthesize smart catalysts, their in-situ characterization, high current density operation, long-term stability, and their practical use in proton exchange membrane water electrolysis (PEMWE).
Figure 1. Three essential features of low-dimensional catalysts for practical applications of acidic OER, including intrinsic activity, high current density operation, and long-term stability.
Intrinsic activity of the catalysts is the principal factor and this can be improved by surface chemistry engineering, using amorphous state, and synergetic effect engineering because these methods can modify electronic structure and binding energy of intermediates. Compared with low current density reaction, high current density OER has put forward higher requirements in terms of the exposure of the active sites, mass transfer, electron transfer and the stability of the electrode. All these factors must be considered for high current density OER operation to be achieved by constructing a porous structure and/or introducing a catalyst support. The catalyst stability includes chemical stability and mechanical stability, and both should be improved in order to achieve long-term stability. The catalyst may suffer from degradation due to its dissolution into electrolyte and/or peeling off from the electrode. Protecting the active sites and strengthening catalyst-support interaction are beneficial for improving the long-term stability of catalysts.
Figure 2. Strategies of engineering the surface chemistry of catalysts to improve their intrinsic OER activity, including heteroatom doping, vacancy engineering, alloying, core-shell construction, and strain regulation.
The review also put forward four aspects for further investigation, including smart catalyst design and synthesis, visualizing in-situ characterizations, high current density operation and long-term stability, and industrial applications of PEMWE.
Figure 3. Prospects for developing acidic OER.
The review entitled “Low-Dimensional Electrocatalysts for Acidic Oxygen Evolution: Intrinsic Activity, High Current Density Operation, and Long-Term Stability”, has recently been published in the journal Advanced Functional Materials. The corresponding authors are Prof. Bilu LIU and Dr. Qiangmin YU. The first author is Shuqi HU, a PhD candidate at Tsinghua SIGS. Authors also include Shiyu GE, Heming LIU, and Xin KANG. This work is supported by the National Science Fund for Distinguished Young Scholars; the National Natural Science Foundation of China; Guangdong Innovative and Entrepreneurial Research Team Program; Guangdong Basic and Applied Basic Research Foundation; Shenzhen Basic Research Project; the Science, Technology, and Innovation Commission of Shenzhen Municipality.
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Written by Shuqi Hu
Edited by Alena Shish & Yuan Yang