From Atomic-Level Synthesis to Device-Scale Reactors: A Multiscale Approach to Water Electrolysis

ConspectusThe development of an advanced energy conversion system for water electrolysis with high efficiency and durability is of great significance for a hydrogen-powered society. This progress relies on the fabrication of electrocatalysts with superior electrochemical performance. Despite decades of advancements in exploring high-performance noble and non-noble metal electrocatalysts, several challenges persist at both the micro- and macrolevels in the field of water electrolysis.At the microlevel, which encompasses electrocatalyst synthesis and characterization, design strategies for high-performance electrocatalysts have primarily focused on interface chemical engineering. However, comprehensive understanding and investigation of interface chemical engineering across various length scales, from micrometers to atomic scales, are still lacking. This deficiency hampers the rational design of catalysts with optimal performance. Under harsh reaction conditions, such as high bias potential and highly acidic or alkaline media, the surface of catalyst materials is susceptible to undergoing "reconstruction", deviating from what is observed through ex situ characterization techniques postsynthesis. Conventional ex situ characterization methods do not provide an accurate depiction of the catalyst's structural evolution during the electrocatalytic reaction, hindering the exploration of the catalytic mechanism.At the macrolevel, pertaining to catalysis-performance evaluation systems and devices, traditional laboratory settings employ a conventional three-electrode or two-electrode system to assess the catalytic performance of electrocatalysts. However, this approach does not accurately simulate hydrogen production under realistic industrial conditions, such as elevated temperatures (60-70 °C), high current densities exceeding 0.5 A cm-2, and flowing electrolytes. To address this limitation, it is crucial to develop testing equipment and methodologies that replicate the actual industrial conditions.In this Account, we propose a multiscale research framework for water electrolysis, spanning from microscale synthesis to macroscale scaled reactor design. Our approach focuses on the design and evaluation of high-performance HER/OER (hydrogen evolution reaction/oxygen evolution reaction) electrocatalysts, incorporating the following strategies: Leveraging principles of interface chemical engineering across various length scales (micrometers, nanometers, and atoms) enables the design of catalyst materials that enhance both activity and durability. This approach provides a comprehensive understanding of the intricate interplay between the catalyst structure and activity, implementing in situ/operando characterization techniques to monitor dynamic interfacial reactions and surface reconstruction processes. This facilitates a profound exploration of catalytic reaction mechanisms, offering insights into the catalyst's structural evolution during the electrocatalytic reaction. We construct a laboratory-scale membrane electrode assembly (MEA) electrochemical reactor capable of operating at high current densities (>1 A cm-2) to evaluate the electrocatalytic performance under simulated industrial conditions. This ensures objective and authentic assessments of the catalyst application potential. Throughout the following sections, we illustrate the application of interface chemical engineering on different length scales in designing diverse electrocatalyst materials. We rely on in situ characterization techniques to gain a profound understanding of the mechanisms behind the HER and OER. Additionally, we describe the development of both acidic and alkaline MEA electrochemical reactors to enhance the precision of electrocatalytic performance evaluation. Finally, we provide a concise overview of the challenges and opportunities in this field.