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, Na4(C4H7N2)[{Mn3WO3}[BiW9O33]2(H3O)8]·7H2O (1), Na7(C3H3N2)[{MnWO3}{BiW9O33}]·14H2O (2). Both compounds, 1 and 2 are
made up of two {BiW9O33}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 {BiW9O33}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 H2SO4) 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), Na12[(Na(H2O)2)6(BiW9O33)2]·27H2O (abbreviated as {BiW9}) (369 mV/534 mV), [{NaO2(H2O)2}2{(Mn(H2O)2)2(WO2)2 (BiW9O33)2}]·16H3O+·XH2O
(abbreviated as {BiW9–Mn})(285 mV/435 mV) at 10
mA cm–2 in 0.5 M H2SO4 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.