Harnessing sonochemistry in MnCoP2O7 as trifunctional electrodes for symmetric supercapacitor and electrochemical water splitting applications

Abstract

Bimetallic pyrophosphates remain relatively unexplored despite their potential for high specific capacitance and electrocatalytic efficiency in an alkaline medium. Notably, this research represents the first successful synthesis of manganese cobalt pyrophosphate, via ultrasonic-assisted synthesis followed by calcination at 500 °C, which plays a pivotal role in energy storage and conversion as an effective catalyst. The samples were systematically characterized to determine their phase composition, structure, functional groups, morphological features, surface elemental composition, and surface area. Our research uncovers that the incorporation of cobalt significantly enhances the electrochemical active sites of the material. The synthesized MnCoP₂O₇ exhibits remarkable specific capacitance and capacity values of 405.2 F g⁻¹ and 202.6 C g⁻¹ in the alkaline electrolyte of 1 M KOH at 1 A g⁻¹, maintaining exceptional stability of 102.8% over 10 000 cycles. Furthermore, the assembled symmetric supercapacitor achieved an energy density of 16.2 Wh kg⁻¹ at a power density of 399.9 W kg⁻¹, retaining 78.2% capacitance over 20 000 cycles. Additionally, MnCoP₂O₇ demonstrates exceptional hydrogen evolution reaction performance, with a low overpotential of 212 mV at a current density of 50 mA cm⁻² and a Tafel slope of 135.6 mV dec⁻¹. Similarly, its oxygen evolution reaction performance evidenced an overpotential of 349 mV at a current density of 50 mA cm⁻² and a Tafel slope of 169.2 mV dec⁻¹. The MnCoP₂O₇ catalyst achieves a current density of 10 mA cm⁻² at a cell voltage of 1.57 V, demonstrating its efficiency for overall water splitting. These values represent the highest performance reported to date for bimetal pyrophosphates in 1 M KOH electrolyte. Furthermore, these findings establish a rational approach for synthesizing electrocatalysts suitable for trifunctional applications.