Electrocatalysts for hydrogen and oxygen evolution reactions under neutral/near-neutral conditions: Summary and challenges

The electrocatalytic hydrogen production via water electrolysis offers a clean, eco-friendly, and renewable pathway to address global challenges of growing energy demand. However, enhancing the efficiency of water splitting process requires the development of cost-effective and robust catalysts with distinctive chemical structures, physical properties, and adequate stabilities. Catalyst degradation, particularly in electrocatalysis, remains a major limitation that decreases the efficiency of electrocatalytic devices. During the water splitting process, controlling the electrolyte pH is an effective strategy to improve catalyst stability by reducing its degradation. Extreme pH values (strongly acidic or basic conditions) typically enhance the reaction kinetics of most water splitting electrocatalysts. However, such extreme conditions can also lead to issues such as accelerated corrosion of cell components, increased energy consumption for electrolyte handling, and limited compatibility with non-metallic or less durable materials. These issues highlight the urgent need for the development of electrocatalysts that retain acceptable activity under neutral or near-neutral conditions. Different types of molecular and heterogeneous catalysts have been explored including nanostructured oxides, hydroxides, phosphides, sulfides, selenides, non-metallic carbonaceous materials, as well as pure metals and alloys. Under such conditions, exceptional electrocatalytic activities (e.g., overpotentials (η₁₀) as low as ∼22 mV and Tafel slopes of ∼21 mV/dec) and stabilities (up to ∼4–5 weeks) have been achieved. This review highlights the diversity and performance of recently developed electrocatalysts for OER and HER in neutral environments, emphasizing their potential to inspire further research in this emerging field.