Heterometallic Polyoxotitanium Clusters as Bifunctional\nElectrocatalysts for Overall Water Splitting

Abstract

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