Boosting alkaline hydrogen evolution via cobalt functionalization of organic–inorganic hybrid germanoniobate electrocatalysts

Abstract

Two organic–inorganic hybrid germanoniobates with analogous supramolecular frameworks H₃Na₂(H₂O)₄[Co^III(en)₃]₆(Co^III(OH)₂(H₂O)₂)[Co^II(en)(H₂O)Ge₄(OH)₂Nb₁₆O₅₄]₂·32H₂O ({Co₉(Ge₄Nb₁₆)₂}, en = ethylenediamine) and Na₄(H₂O)₁₀(H₂en)₅ [Ge₄(OH)₂Nb₁₆O₅₄]·15H₂O ({Ge₄Nb₁₆}), have been successfully built from {Ge₄(OH)₂Nb₁₆O₅₄} polyoxoanions functionalized with either the Co–amine complex or en organic ligand. Compound {Co₉(Ge₄Nb₁₆)₂} represents the first example of a germanoniobate incorporating both Co^II and Co^III complexes. Both compounds form three-dimensional supramolecular structures with an unusual eight-connected hex-type topology. Electrochemical experiments demonstrate that the Co-containing {Co₉(Ge₄Nb₁₆)₂} exhibits significantly enhanced hydrogen evolution reaction (HER) activity under strongly alkaline conditions compared to the Co-free analogue {Ge₄Nb₁₆}. This finding highlights the crucial role of cobalt in promoting electrocatalytic performance. This work provides molecular-level insights into how deliberate structural modification of polyoxometalates (POMs) modulates their electrocatalytic HER activity.