A [Co₁₉(OH)₁₂]²⁶⁺-Incorporating Polyoxotungstate for Electrocatalytic Oxygen Evolution

Considerable efforts have been devoted to the research of transition-metal oxides for oxygen evolution reaction (OER) catalysts. Polyoxometalates (POMs) are one of the typical compounds of transition-metal oxides. In particular, cobalt-containing POMs have attracted much attention as potential catalysts for the OER. In this work, a new [Co₁₉(OH)₁₂]²⁶⁺ unit-incorporating polyoxotungstate, Na₃₄[Co₁₉(OH)₁₂(α-SiW₁₀O₃₇)₆]·46H₂O (referred to as CoSiW), has been successfully prepared and explored for highly efficient OER. The most obvious feature is that the giant [Co₁₉(OH)₁₂(α-SiW₁₀O₃₇)₆]^34- subunit in CoSiW consists of six dilacunary Keggin-type [α-SiW₁₀O₃₇]^10- groups interlaced and wrapped around a hexagonal-like [Co₁₉(OH)₁₂]²⁶⁺ nanosheet, forming a sandwich-type structure. Furthermore, in comparison with other well-known Co-containing Keggin-type POMs of [Co₄(H₂O)₂(α-PW₉O₃₄)₂]^10- (denoted as Co₄(PW₉)₂) and [α-CoW₁₂O₄₀]^6- (denoted as CoW₁₂) as well as cobalt oxide (CoO), the CoSiW electrocatalyst exhibits an overpotential of 329.4 mV at 10 mA·cm^-2, a low Tafel slope of 80.8 mV·dec^-1, and a high stability in 0.1 M KOH electrolyte for over 40 h at 60.0 mA·cm^-2. The hydroxyl bridges in CoSiW characterized by cooperative Co-O-Co interactions and multiple catalytic active sites act as a key factor in improving the electrocatalytic performance of POMs, thereby offering a cost-effective electrocatalyst with potential applications in renewable energy.