Proton conduction facilitates the hydrogen evolution reaction in heptamolybdate-protected SnO 2 nanocore

Abstract Recently, the Anderson-type heptamolybdate [Mo7O24]6- ion has been used as an inorganic ligand to protect various metal oxy-hydroxides (FeOOH and NixFe1-xOOH) and oxides (SnO2 and CeO2), and these unique varieties of materials are employed as electrode materials for water oxidation and nitrate reduction. Herein, [Mo7O24]6- covalently connected to a SnO2 nanocore, namely Mox@SnO2, is prepared through a hydrothermal route and has been fabricated on a 1 cm2 surface of a conducting carbon support to study proton conduction and electrocatalytic proton reduction. The Mox@SnO2 fabricated carbon cloth (CC) exhibits the maximum proton conductivity of 15.34 × 10−3 S cm-1 at pH 3.65 and room temperature, which increased linearly with the increment in cell temperature and reached 32.47 × 10−3 S cm−1 at 318 K. Under similar conditions, the bare SnO2 fabricated on CC shows relatively low proton conductivity, highlighting the importance of POM ligands on Mox@SnO2 to facilitate proton conduction with an extremely low activation energy of 0.13 eV, indicative of proton shuttling through the Grotthuss pathway. Further, the facile proton conduction on Mox@SnO2 and the redox participation of POMs, as depicted from cyclic voltammetric studies, enable electrocatalytic hydrogen evolution reaction (HER) under mild acidic conditions, delivering an onset potential of -0.4 V vs RHE and a nearly two-fold higher catalytic current at -0.9 V compared to that observed for SnO2. The electrokinetic study has confirmed that the improved performance of Mox@SnO2 over SnO2 is due to enhanced charge-transfer kinetics. This study showcases a new role for covalently attached heptamolybdate anions on SnO2, facilitating proton relay and reduction.