Transition-metal phosphides (TMPs) enjoy metalloid characteristics with good electrical conductivity, making them potential candidates for electrochemical supercapacitors. However, TMPs are difficult to synthesize by conventional methods, limiting their practical use in a plethora of applications. Herein, we demonstrate the successful fabrication of Ni–Cu binary phosphides (NCP) via a one-step, facile solvothermal method. More importantly, the correlation between the degree of phosphidation and the electrochemical behavior of the material is explored and discussed. The NCP electrode exhibited a battery-like behavior with an ultrahigh specific capacitance (C s) of 1573 F g–1 at 1 A g–1. Upon use as a positive electrode, it showed superior performance in a hybrid supercapacitor device with bioderived activated carbon (BAC) as the negative electrode (NCP//BAC), providing a high energy density of 40.5 W h kg–1 at 875 W kg–1 with exceptional capacity retention after 10,000 cycles. These values are 4 times higher than that of commercial supercapacitors (10–12 W h kg–1), suggesting the unique supercapacitance performance of the NCP//BAC device compared to the phosphide-based devices reported so far.

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The facile fabrication of functional supercapacitor electrodes with desirable characteristics is a bottleneck challenge to advance the supercapacitor industry. Among those functional materials, metal phosphides and sulfides have been explored separately with various pros and cons. Herein, we report a facile one-step electrodeposition method for the preparation of bimetallic thiophosphide (FNSP) based electrodes that comprise the advantages of both sulfides and phosphides simultaneously. Upon use as a supercapacitor electrode, FNSP shows an exceptionally high specific capacity of 1415.20 C/g at 1 A/g. Moreover, the assembled AC//FNSP asymmetric device reveals outstanding performance with a high energy density of 52.42 Wh/kg corresponding to a power density of 1.70 kW/kg at 2 A/g with superior Coulombic efficiency and cycling stability over 10 000 cycles. The obtained performance metrics demonstrate the superb performance of the fabricated AC// FNSP device over the sulfide or phosphide alone based devices reported so far. The exceptional specific capacitance of the FNSP electrode is attributed to the synergy between S and P in the fabricated electrode that improves the conductivity and provides more electrochemical active sites.