Key points are not available for this paper at this time.
Monoclinic Co2–xNixP2O7 (x = 0.00–2.00) pyrophosphates were synthesized and composition-tuned to reveal an optimal morphology/porosity at x = 1.00 that delivered high-performance supercapacitor electrodes. Across the series, X-ray diffraction (XRD) results confirmed a pure phase of Co2–xNixP2O7 (P21/c), with Ni substitution providing acceptable crystallite-size shifts and a systematic lattice shrinkage. Field emission scanning electron microscopy (FE-SEM) showed that x = 1.00 specimen formed well-faceted octagonal microplates with the highest specific surface area (11.381 m2/g) and mesoporous surfaces with average pore sizes of ∼10 nm and mesopore volume of 0.0909 cm3/g, as revealed by Brunauer–Emmett–Teller/Barett–Joyner–Halenda (BET/BJH) analysis. X-ray photoelectron spectroscopy (XPS) identified Co2+, Ni2+, and P5+, which is consistent with OH–-coupled M2+/M3+ pseudocapacitance observed using cyclic voltammetry (CV)/galvanostatic charge–discharge (GCD) in 3 M KOH. The x = 1.00 electrode achieved 654 F/g at 0.5 A/g and maintained 84.6% of its initial state after a 3000-cycle GCD test at 5 A/g. An asymmetric device (Co1.00Ni1.00P2O7//rGO) delivered 56.68 Wh/kg at 938.36 W/kg. Electrochemical enhancement resulted from a combination of mixed-metal redox centers and optimized meso-porosity/microstructure, as evidenced by CV, GCD, and electrochemical impedance spectroscopy (EIS). The findings demonstrated that compositional control presented an effective strategy for controlling mesoporousity and enhancing redox utilization in Co–Ni pyrophosphate electrodes.
Wannasen et al. (Thu,) studied this question.