A Facile Synthetic Strategy for Decavanadate and Transition Metal Based All-Inorganic Coordination Polymers and Insights into Their Electrocatalytic OER Activity

This study reports a facile synthetic strategy for decavanadate ([V10O28](6-)) cluster-based all inorganic coordination polymers (CPs) containing earth-abundant and redox-active transition metals and their electrocatalytic oxygen evolution reaction (OER) activity. The first series of such isomorphous compounds containing the transition metals Mn, Co, and Ni, {(H2O)(2)K-mu-(H2O)(3)Mn(H2O)(3)}(2n)[V10O28](n) (1), {(H2O)(2)K-mu-(H2O)(3)Co(H2O)(3)}(2n)[V10O28](n) (2) and {(H2O)(2)K-mu-(H2O)(3)Ni(H2O)(3)}(2n)[V10O28](n) (3), have been synthesized and structurally characterized. In these polymeric compounds, the [V10O28](6-) clusters are interlaced and inter-connected by {(H2O)(2)K-mu-(H2O)(3)-M(H2O)(3)}(+3) units leading to a linear chain-like arrangement. Each of such chains is further interconnected to adjacent chains by bonding K+ ions with a [V10O28](6-) cluster of the adjacent chain leading to a two-dimensional (2D) sheet-like arrangement. Hydrogen bonding interactions between the coordinated water molecules and the cluster oxygens further interconnect the adjacent sheets. All these compounds 1-3 are shown to catalyze the oxygen evolution reaction (OER) under alkaline (0.1 M KOH) conditions. Among the three, the Ni-based catalyst 3 exhibited the best OER activity with a moderate overpotential of 270 mV at onset, a low Tafel slope of 89 mV dec(-1), and a turnover frequency (TOF) of 7.5 s(-1), which is comparable to similar Keggin POM-based systems reported so far. The CPs were not highly stable under the OER conditions employed. The post-catalytic analyses indicated the 'precatalyst' nature of these compounds in alkaline media forming V-doped metal oxyhydroxides as the OER active species under the turnover conditions. Thus, this study provides a new and facile strategy for synthesizing [V10O28](6-)cluster and transition metal-based all-inorganic CPs and insights into their OER electrocatalytic activities for the first time.

Automated summary

This study presents a facile synthetic strategy for the synthesis of all inorganic coordination polymers based on decavanadate clusters. These polymers exhibit electrocatalytic activity for the oxygen evolution reaction under alkaline conditions, with the nickel-based catalyst showing the highest activity.