Mn-Based Polyoxometalates with Organic–Inorganic Large-Spaced Layers as the Highly Efficient Electrocatalysts for Acidic and Alkaline Hydrogen Evolution Reaction

Polyoxometalates are promising options for electrocatalysts due to electronic sponges properties. Organic–inorganic hybridized polyoxometalates are the focus of research in the field of electrocatalytic hydrogen evolution through substitution by transition metal ions or modification by organic ligands. Using a one-step solution method, two new Mn-based polyoxometalates were successfully created, Na 4 (C 4 H 7 N 2 )[{Mn 3 WO 3 }[BiW 9 O 33 ] 2 (H 3 O) 8 ]·7H 2 O (1), Na 7 (C 3 H 3 N 2 )[{MnWO 3 }{BiW 9 O 33 }]·14H 2 O (2). Both compounds, 1 and 2 are made up of two {BiW 9 O 33 } 9– polyoxyanions encapsulated in 10-nuclear high-nuclear clusters containing Mn ions and further connected to organic ligands through hydrogen bonding. It is worth noting that compound 1 forms large-spaced organic–inorganic layered three-dimensional structures with two {BiW 9 O 33 } 9– polyoxyanions encapsulating 10-nuclear high-nuclear clusters containing Mn ions as the inorganic layer and 2-methylimidazole ligand as the organic layer eventually. However, compound 2 forms a three-dimensional structure with an imidazole ligand organic layer wrapped in an inorganic layer. The two compounds were used in the electrocatalytic hydrogen evolution reaction (HER) in acidic solutions (0.5 M H 2 SO 4 ) and alkaline solutions (1 M KOH). Compound 1 has exceptional catalytic activity, with overpotential values of 30 and 140 mV, respectively, which were significantly lower than compound 2 (74 mV/328 mV), Na 12 [(Na(H 2 O) 2 ) 6 (BiW 9 O 33 ) 2 ]·27H 2 O (abbreviated as {BiW 9 }) (369 mV/534 mV), [{NaO 2 (H 2 O) 2 } 2 {(Mn(H 2 O) 2 ) 2 (WO 2 ) 2 (BiW 9 O 33 ) 2 }]·16H 3 O + ·XH 2 O (abbreviated as {BiW 9 –Mn})(285 mV/435 mV) at 10 mA cm –2 in 0.5 M H 2 SO 4 and 1 M KOH electrolyte solution. Meanwhile, compound 1 showed excellent durability (1000 cycles) and stability (24 h) under both conditions. This study provides a new and convenient way to design organic–inorganic layered polyoxometalates for electrocatalytic hydrogen evolution reactions.