Scalable solvent-mediated nanoarchitectonics of high-surface-area mesoporous Ni₂P₂O₇ for enhanced electrochemical performance in alkaline media

Abstract

Sol–gel synthesis provides a versatile and scalable route for producing high-surface-area materials. Here, we develop a facile sol–gel strategy for mesoporous nickel pyrophosphate Ni₂P₂O₇ using H₄P₂O₇, nickel nitrate, and Pluronic P123 in butanol- and ethanol-based media. These mixtures form homogeneous sols that gelate and, after drying and calcination at 300 °C, yield powders with surface areas up to 410 m² g⁻¹. In contrast, methanol systems─and certain ethanol conditions─phase-separate into precipitate and supernatant layers. After calcination, the solution and precipitate fractions produce mesoporous Ni₂P₂O₇, while the supernatant fraction forms Ni₃(PO₄)₂ with different textural properties. The materials remain amorphous up to 600 °C and crystallize into α-Ni₂P₂O₇ at 700 °C. Thin-film electrodes were prepared by spin-coating on fluorine-doped tin oxide and dip-coating on graphite, followed by calcination. In 1 M KOH, Ni₂P₂O₇ converts into ultrafine Ni(OH)₂ nanoflakes, with the transformed graphite-supported electrodes showing high oxygen evolution reaction (OER) activity and stability. Moreover, Ni₂P₂O₇ is stable in alkaline media (pH ∼13) when the P₂O₇⁴⁻ concentration exceeds ∼0.27 M in the electrolyte. This work demonstrates a simple, tunable route to mesoporous Ni₂P₂O₇ and reveals its conversion into highly active OER electrocatalysts (381 mV at 100 mA cm–2, 45 mV dec–1).