Novel components in Proton Exchange Membrane (PEM) Water Electrolyzers (PEMWE): Status, challenges and future needs. A mini review

Electrochemical water splitting represents one of the most promising technologies to produce green hydrogen, which can help to realize the goal of achieving carbon neutrality. While substantial efforts on a laboratory scale have been made for understanding fundamental catalysis and developing high-performance electrocatalysts for the two half-reactions involved in water electrocatalysis, much less attention has been paid to doing relevant research on a larger scale. For example, few such researches have been done on an industrial scale. Herein, we review the very recent endeavors to bridge the gaps between fundamental research and industrial applications for water electrolysis. We begin by introducing the fundamentals of electrochemical water splitting and then present comparisons of testing protocol, figure of merit, catalyst of interest, and manufacturing cost for laboratory and industry-based water-electrolysis research. Special attention is paid to tracking the surface reconstruction process and identifying real catalytic species under different testing conditions, which highlight the significant distinctions of corresponding electrochemical reconstruction mechanisms. Advances in catalyst designs for industry-relevant water electrolysis are also summarized, which reveal the progress of moving the practical applications forward and accelerating synergies between material science and engineering. Perspectives and challenges of electrocatalyst design strategies are proposed finally to further bridge the gaps between lab-scale research and large-scale electrocatalysis applications. 

https://onlinelibrary.wiley.com/doi/pdfdirect/10.1002/eem2.12441

Electrochemical Water Splitting: Bridging the Gaps between Fundamental Research and Industrial Applications

Developing an efficient and non‐precious pH‐universal hydrogen evolution reaction electrocatalyst is highly desirable for hydrogen production by electrochemical water splitting but remains a significant challenge. Herein, a hierarchical structure composed of heterostructured Ni2P‐Ni12P5 nanorod arrays rooted on Ni3S2 film (Ni2P‐Ni12P5@Ni3S2) via a simultaneous corrosion and sulfidation is built followed by a phosphidation treatment toward the metallic nickel foam. The combination of theoretical calculations with in/ex situ characterizations unveils that such a unique sequential phase conversion strategy ensures the strong interfacial coupling between Ni2P and Ni12P5 as well as the robust stabilization of 1D heteronanorod arrays by Ni3S2 film, resulting in the promoted water adsorption/dissociation energy, the optimized hydrogen adsorption energy, and the enhanced electron/proton transfer ability accompanied with an excellent stability. Consequently, Ni2P‐Ni12P5@Ni3S2/NF requires only 32, 46, and 34 mV overpotentials to drive 10 mA cm−2 in 1.0 m KOH, 0.5 m H2SO4, and 1.0 m phosphate‐buffered saline electrolytes, respectively, exceeding almost all the previously reported non‐noble metal‐based electrocatalysts. This work may pave a new avenue for the rational design of non‐precious electrocatalysts toward pH‐universal hydrogen evolution catalysis.

Sequential Phase Conversion‐Induced Phosphides Heteronanorod Arrays for Superior Hydrogen Evolution Performance to Pt in Wide pH Media

Transition metals, in particular noble metals, are the most common species in metal‐mediated water electrolysis because they serve as highly active catalytic sites. In many cases, the presence of nontransition metals, that is, s‐, p‐, and f‐block metals with high natural abundance in the earth‐crust in the catalytic material is indispensable to boost efficiency and durability in water electrolysis. This is why alkali metals, alkaline‐earth metals, rare‐earth metals, lean metals, and metalloids receive growing interest in this research area. In spite of the pivotal role of these nontransition metals in tuning efficiency of water electrolysis, there is far more room for developments toward a knowledge‐based catalyst design. In this review, five classes of nontransition metals species which are successfully utilized in water electrolysis, with special emphasis on electronic structure–catalytic activity relationships and phase stability, are discussed. Moreover, specific fundamental aspects on electrocatalysts for water electrolysis as well as a perspective on this research field are also addressed in this account. It is anticipated that this review can trigger a broader interest in using s‐, p‐, and f‐block metals species toward the discovery of advanced polymetal‐containing electrocatalysts for practical water splitting.

The Pivotal Role of s‐, p‐, and f‐Block Metals in Water Electrolysis: Status Quo and Perspectives

The development of robust nano‐ and microstructured catalysts on highly conductive substrates is an effective approach to produce highly active binder‐free electrodes for energy conversion and storage applications. As a result, nanostructured electrodes with binder‐free designs have abundant advantages that provide superior electrocatalytic performance; these include more exposed active sites, large surface area, strong adhesion to substrates, facile charge transfer, high conductivity, high intrinsic catalytic activity, and fine‐tuning of its electronic nature through nanostructure modification. Notably, the interface chemistry of an electrocatalyst plays a significant role in their optimized electrocatalytic activity and stability. This review provides an overview of recent progress in nano‐ and microstructured catalysts, such as one, two, and 3D catalysts as binder‐free electrodes for electrocatalytic water splitting via the hydrogen evolution reaction and oxygen evolution reaction, and beyond. Furthermore, this review focuses on the current challenges and synthesis strategies of binder‐free electrodes, with a focus on the impact of nanostructure on their functional property relationships and enhanced bifunctional electrocatalytic performance. Finally, an outlook for their future advances in energy conversion and storage is provided.

Hongyuan Yang

Papers

Self-Supported Electrocatalysts for Practical Water Electrolysis