Cu-pyrazolate cluster-based halogen-rich magnetic MOFs for electrochemical water splitting.

The main theme of interest of the current study is to evaluate the electrochemical water splitting activity of Cu-cluster-based MOFs, generated using the node-spacer concept. Accordingly, a series of Cu-MOFs were constructed using an inorganic cluster, namely, the trinuclear Cu-pyrazolate [Cu3(μ3-OH)(μ-Pyz)3] (TCuP) moiety, as the node, and various halogen-substituted dicarboxylic acids as spacers. The recurrence of networks comprising the TCuP motif node not only supports the robustness and reproducibility of the synthetic strategy but can also be envisaged as successful improvisation for the periodic grafting of a potentially important water oxidation catalytic site inside the framework. Furthermore, strategically chosen linkers with immobilized halogens, in their part, vindicate our thematic aim of forming peripheral hedges to exert a positive impact on the local electronic environment of the OER site (TCuP) by instigating charge species formation as well as transportation, a potentially crucial facilitator for electrocatalysis. Comprehensive electrochemical water splitting studies under alkaline media were carried out to evaluate the importance of the TCuP-based MOFs as water oxidation catalysts. The results, presented in terms of overpotential, electrocatalytic surface area values and Tafel slopes, are gratifying and highly competitive to those of well-known published systems. Finally, the presence of Cu6 units, comprising two triangular hydroxy-bridged tris Cu-pyrazolate motifs, as nodes enhances the prospective use of these MOFs as magnetic materials. Accordingly, detailed magnetic studies of TCuP-2 and TCuP-3 were carried out, which show interesting magnetic features, including encouraging cryogenic magnetic refrigeration with respective -ΔSM values of 7 J kg-1 K-1 and 6.1 J kg-1 K-1 at T = 2 K for a field change of ΔH = 7 T.