Heterometallic Polyoxotitanium Clusters as Bifunctional Electrocatalysts for Overall Water Splitting

Abstract

Incorporating heterometal into titanium-oxygen clusters (TOCs) is an effective way to improve its catalytic activity. Herein, we synthesize three novel heterometallic TOCs with the formula of [Ti₆Cu₂O₇(Dmg)₂(OAc)₄(ⁱPrO)₆][H₂Ti₆Cu₂O₇(Dmg)₂(OAc)₄(ⁱPrO)₈] ({Ti₆Cu₂}), [Ti₈Cu₂O₉(Dmg)₂(OAc)₂(ⁱPrO)₁₂] ({Ti₈Cu₂}), and [Ti₁₀Co₂O₆(Dmg)₂(Pdc)₄(ⁱPrO)₁₈Cl₃] ({Ti₁₀Co₂}, DmgH₂ = dimethylglyoxime; PdcH₂ = pyridine-2,3-dicarboxylic acid) using dimethylglyoxime and different carboxylates as the synergistic ligands. By depositing the clusters {Ti₆Cu₂} and {Ti₁₀Co₂} on carbon cloth as electrodes, we investigated the electrocatalytic performance of TOCs for full water splitting for the first time. To reach a 10 mA cm^-2 current density in an alkaline solution, the {Ti₁₀Co₂}@CC electrode needs an overpotential as low as 120 and 400 mV for the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER), respectively. In addition, full water-splitting equipment with {Ti₁₀Co₂}@CC as a cathode and an anode need only 1.67 V to deliver a current density of 10 mA cm^-2. Our work confirmed the potential of noble metal-free TOCs as bifunctional cluster-based electrocatalysts for water splitting, and their activities can be tuned by doping with different metal ions.