A pH-Tolerant Nickel-Vanadium Phosphonate Framework for Stable Aqueous Supercapacitor Cycling.
basic_science · Level V
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- Record sourced from PubMed, PMID 42406492.
- Also identified by DOI 10.1021/acsnano.6c02468.
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Abstract
We report a hybrid layered metal-phosphonate framework, [Ni(2,2'-bpy)<sub>3</sub>]<sup>2+</sup>[(VO(H<sub>2</sub>O))<sub>2</sub>(VO)<sub>4</sub>(μ-O)<sub>2</sub>(C<sub>6</sub>H<sub>5</sub>PO<sub>3</sub>)<sub>6</sub>]<sup>2-</sup>·2H<sub>2</sub>O, in which redox-active [(Ni(2,2'-bpy)<sub>3</sub>)]<sup>2+</sup> cations are embedded between anionic vanadium phosphonate layers [(VO(H<sub>2</sub>O))<sub>2</sub>(VO)<sub>4</sub>(μ-O)<sub>2</sub>(C<sub>6</sub>H<sub>5</sub>PO<sub>3</sub>)<sub>6</sub>]<sup>2-</sup> (with 2,2'-bpy = 2,2'-bipyridine). X-ray photoelectron spectroscopy reveals coexisting Ni<sup>2+</sup>, V<sup>2+</sup>, V<sup>3+</sup>, and V<sup>4+</sup>/V<sup>5+</sup> species on the surface of the crystals, indicating a highly dynamic redox system. The material exhibits a main photoluminescence peak at 2.25 eV and strong short-range antiferromagnetic coupling between the V<sup>4+</sup> centers. Electrochemical characterization in aqueous media yields capacitances of 79 F/g in Na<sub>2</sub>SO<sub>4</sub> (pH 7) and 43 F/g in H<sub>3</sub>PO<sub>4</sub> (pH 4) at 1 A/g. In Na<sub>2</sub>SO<sub>4</sub> (pH 7), the material reaches about 300 F/g at a scan rate of 1 mV/s and retains capacity over more than 10,000 cycles. The crystals remain chemically stable between pH 2 and pH 10 for at least 1 week. Combined sustainable synthesis, robust redox activity, high capacitance, long cycle stability, and broad pH tolerance make these hybrid metal-phosphonate crystals promising candidates for next-generation aqueous energy-storage applications.