Design of noble metal catalysts and reactors for the electrosynthesis of hydrogen peroxide

Hydrogen peroxide (H2O2) is an eco-friendly oxidant vital for chemical synthesis, water treatment, and disinfection. However, the conventional anthraquinone production method is energy-intensive, generates waste, and requires hazardous transport of concentrated H2O2. Electrochemical H2O2 synthesis via a two-electron oxygen reduction reaction (2e- ORR) has emerged as a sustainable alternative, enabling renewable-powered, decentralized production under mild conditions. Noble metal catalysts outperform alternatives in acidic media, demonstrating superior stability and selectivity. Despite these advantages, several technical challenges must be addressed to enable industrial-scale implementation. The primary challenge lies in optimizing catalyst performance to achieve both high activity and selectivity for the 2e- pathway while suppressing the competing 4epathway that produces water. This requires precise control of the catalyst's electronic and surface structures. Additionally, the development of cost-effective reactor systems that can maintain high performance at scale presents another significant hurdle. Current research focuses on improving mass transport, current distribution, and product separation while minimizing energy consumption. This review provides a comprehensive examination of recent progress in the 2e- ORR, with particular emphasis on noble metal catalysts and reactor engineering. We begin by discussing the fundamental principles and reaction mechanisms underlying the 2e- ORR, emphasizing the role of material design in optimizing catalytic performance. Noble-metal catalysts are categorized into four types, namely, pure metals, alloys, compounds, and single-atom catalysts, with a critical evaluation of their performance based on theoretical and experimental findings. The second part of the review focuses on reactor design strategies for practical applications. We evaluate reactor designs, including H-cells, flow cells, membrane electrode assemblies, and solid-state electrolyte cells, with a focus on their mass transport and scalability characteristics. Particular emphasis is placed on gas diffusion electrodes for improved oxygen accessibility and innovative in situ product separation methods. Finally, we discuss the remaining challenges and future directions, including the need for reduced noble metal loading, improved long-term stability, and system integration with renewable energy sources. The review concludes by highlighting the tremendous potential of electrochemical H2O2 production to transform industrial oxidation processes while contributing to the development of sustainable chemical manufacturing.