Photocatalytic Seawater Splitting by Earth‐Abundant Catalysts: Metal‐Semiconductor Metamaterials Made of Plasmonic Magnesium Diboride and Transitional Metal Dichalcogenides

Metal-semiconductor metamaterials hold great promise for photocatalytic water splitting due to their excellent light harvesting in a broad spectral range as well as efficient charge carrier generation and transfer. In the majority of such metamaterials, semiconductors are used to initiate the water splitting reaction, while their metal counterparts are employed to improve light harvesting through plasmonic effects. Here, we describe for the first time an exceptional reversed case of metal-semiconductor photocatalysts in which metals are used to initiate the water splitting reaction and semiconductors are employed to improve light harvesting through the blackbody effect and serve as co-catalysts. The studied photoanodes are made of non-noble plasmonic MgB₂ combined with transition metal dichalcogenides (TMDCs). The plasmonic resonances of the MgB₂ component contribute to field confinement, plasmon-exciton coupling, and hot-electron transfer providing an enhancement of photoactivity in the entire solar spectrum capable of water splitting. The TMDC component provides impedance matching and enhances light absorption by the metal catalyst. We demonstrate seawater splitting with MgB₂-TMDCs photoanodes attaining current densities of ~3 mA cm^-2 at solar radiation. The overall efficiency of hydrogen production in seawater splitting by sunlight with the help of the studied photoanodes is 3 % at a bias voltage of V_bias=0.3 V.