Electrocatalysts for Hydrogen and Oxygen Evolution
Hydrogen is one of the most valuable energy carriers and a clean and renewable energy supply. Electrolysis of water, that is, water splitting into hydrogen and oxygen gases under an electrical bias, offers a near-term and long-term solution for the production of hydrogen gas as fuel and for chemical products with large-scale capability. Coupling electricity from photovoltaic or wind farms and hydropower plants with electrolysis can provide a sustainable energy supply without creating environmental problems.
Worldwide, researchers and technologists are working towards improvement of materials which increase the energy conversion efficiency and lower the cost of components and systems for renewable energy conversion and storage. The progress is encouraging.
Electrocatalysts are critical assistants in electrolysis, largely determining its energy conversion efficiency, cost, lifetime, etc. The large voltage for water splitting comes from the ohmic resistance, and anode and cathode overpotentials. Many efforts have been devoted to developing catalysts with small overpotentials. Rare noble metals and their oxides are state-of-the-art electrocatalysts for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), respectively, with good efficiency and lifetime. Their scarcity, however, causes high prices and limited usage, severely restricting the deployment of electrolysis technology for large-scale fuel production. Research has turned to development of earth-abundant, low-cost and highly active catalysts, such as NiFe layered double hydroxide for OER, non-noble metal dichalcogenides and phosphides for HER. Recent years have witnessed a burst of research results in the search for good electrocatalysts, and the papers collected in this JMR Focus Issue represent the broad spectrum of the field’s rapid advancement.