Reconstruction and immobilization of polymolybdate induced by metal–organic coordination units for enhanced electrocatalytic hydrogen generation

Abstract

Electrocatalytic water cracking for hydrogen evolution has drawn attention from researchers owing to its high efficiency. Polymolybdate has excellent redox behaviors and an O-rich surface, becoming attractive electrocatalytic materials. In this work, iso- and hetero-polymolybdate anions were introduced in the crystalline metal–organic coordination system as electrocatalytic electrode material for hydrogen evolution reactions. Semi-rigid bi-pyrazole bi-amide ligand was taken as the organic component, and four complexes were yielded under hydrothermal conditions. The reconstruction and oriented immobilization of polymolybdate occur during the assembly of the architectures, owing to the potential template effect from the metal–organic units. This phenomenon influences the distribution of active sites from polymolybdate. The discrete [AlMo₆(OH)₇O₁₇]²⁻ anions in complex 3 were immobilized among the directionally arranged metal–organic chains and exposed more active sites. The carbon cloth-based electrode modified by complex 3 possesses obvious electrocatalytic activity by achieving a low overpotential of 17.0 mV at a current density of 10 mA cm⁻² in 1 M KOH for the hydrogen evolution reaction. Meanwhile, an overpotential of 33.7 mV can be achieved when the current density is 10 mA cm⁻² in simulated seawater.