Emerging porous solids for electrocatalytic and photocatalytic seawater splitting

Direct splitting of the seawater by renewable energy sources is pivotal to the practical production of hydrogen because of the reduced energy and cost of water purification. However, formidable challenges remain for realizing the direct utilization of seawater for hydrogen production due to the slow water splitting reaction kinetics under the near-neutral condition (approximately pH 8.0) and the occurrence of side reactions originating from the impurities in the seawater. Design concepts of the catalysts compatible with direct seawater splitting are thus greatly needed to satisfy both catalytic activity and selectivity, and porous solid materials such as metal–organic frameworks and covalent organic frameworks have emerged as a new class of electrocatalysts or photocatalysts toward the direct seawater splitting. Herein, we review the current status of the porous solid materials as new catalyst materials by placing emphasis on the structural features that make these materials particularly attractive for seawater splitting: Non-pyrolyzed porous solid structures, which preserve their inherent porosity and properties of organic linkers, have shown great promises in particular. We also point to the existing limitations and future research directions for placing porous solid-based electrocatalysts and photocatalysts on the horizon of a sustainable energy future.