Deciphering the In Situ Surface Reconstruction of Supercapacitive Bimetallic Ni-Co Oxyphosphide during Electrochemical Activation Using Multivariate Statistical Analyses

Abstract

Electrochemical energy storage (EES) technologies are playing a leading role in the global effort to address the energy challenges. Current EES systems are limited by their energy density, capacity, and cycling stability. Some of those limitations arise from nanoscale phenomena, which are not fully understood or accounted for. Electrochemical activation (ECA), an often-overlooked process, creates more active sites on the electrode material and boosts the activity of the system to achieve a higher storage capacity. Herein, the ECA of bimetallic Ni–Co oxyphosphides is investigated via a plethora of spectroscopic techniques, including transmission electron microscopy enhanced by multivariate statistical analysis as a tool to better analyze the obtained spectra. Interestingly, ECA induces an in situ reconstruction of the pre-electrode via phosphorus leaching, together with accelerated surface segregation of the reconstructed Ni and Co species. The electrodes with reconstructed composition showed 110% higher supercapacitive performance than their pre-electrode counterparts. Thanks to the electrochemical optimization approach, a hybrid device has been assembled with a superb performance. The device exhibits energy density values comparable with batteries: 89 W h kg–1 at a power density of 848 W kg–1 with an excellent stability over 10,000 galvanic charge–discharge cycles as manifested by the steady capacitive retention (94.2–100.9%) even during the last 1000 cycles.

Highly Durable Compositionally Variant Bifunctional Tetrametallic Ni–Co–Mn–Fe Phosphide Electrocatalysts Synthesized by a Facile Electrodeposition Method for High-Performance Overall Water Splitting

“…As for the Ni spectrum, the peaks recorded at 856.2 eV and 878 indicate the presence of Ni 2+ species Ni 2p 3/2 and Ni 2p 1/2 , respectively . Besides, the two peak characteristics of oxidized nickel phosphide (Ni–PO x ) were observed at 873.2 eV (2p 1/2 ) and 856.2 eV (2p 3/2 ) . The manganese spectrum showed that the dominant phase formed is Mn 3+ (2p 3/2 ), as indicated by the peak with the highest intensity at 642.7 eV. , Note that a small peak related to Mn 2+ was also observed after deconvolution at 640 eV, along with the characteristic satellite signal of Mn 2+ at 646.5 eV. , The Fe 2p spectrum showed two peaks at 711.9 and 722 eV, with the peak at 714 eV attributed to the oxidized Fe–P .…”

“…66 Besides, the two peak characteristics of oxidized nickel phosphide (Ni−PO x ) were observed at 873.2 eV (2p 1/2 ) and 856.2 eV (2p 3/2 ). 67 The manganese spectrum showed that the dominant phase formed is Mn 3+ (2p 3/2 ), as indicated by the peak with the highest intensity at 642.7 eV. 68,69 Note that a small peak related to Mn 2+ was also observed after deconvolution at 640 eV, along with the characteristic satellite signal of Mn 2+ at 646.5 eV.…”

“…Interestingly, although NiCoMnFe−P2 exhibits lower overpotential, NiC-oMnFe−P1 shows higher stability over the operating time. This might be attributed to the higher rate of P dissolution in NiCoMnF−P2 67 compared to the higher ability of NiC-oMnF−P1 to preserve the P species. The XPS spectra of the catalysts after measurements were collected and analyzed, S1, the energy barrier of the rate-determining step was calculated according to the values of ΔG2 and ΔG3 of each composite.…”

NiFeZnP Nanosheets with Enriched Phosphorus Vacancies for Supercapattery Electrodes

“…Among these energy storage devices, supercapacitors (SCs) enjoy the merits of superb reversibility, high power output, and very long cycle life. − Based on the energy storage mechanism, supercapacitor electrodes can be classified into the following: (1) electrochemical double layer electrodes (EDL) such as carbon-based materials, where the charge is physically stored by electrostatic charge adsorption at the electrode/electrolyte interface; (2) pseudo-capacitive electrodes, which store charges via surface intercalation and diffusion processes; and (3) battery-type electrodes, which involve diffusion and redox reaction processes . Although the performance of supercapacitors is between conventional capacitors (very low energy density) and batteries (low power density), there is still a room to identify and fabricate robust and cheap supercapacitor electrode materials that can deliver high energy density and excellent electrochemical performance . This can be attained by devising a supercapattery, a hybrid device that includes different electrode materials with different charge storage mechanisms, such as combining an EDL electrode with a battery-type electrode. , For battery-type electrodes, materials such as transition metal oxides, hydroxides, nitrides, and sulfides as well as conductive polymers have been extensively investigated as potential candidates. ,− …”

“…9 Although the performance of supercapacitors is between conventional capacitors (very low energy density) and batteries (low power density), there is still a room to identify and fabricate robust and cheap supercapacitor electrode materials that can deliver high energy density and excellent electrochemical performance. 10 This can be attained by devising a supercapattery, a hybrid device that includes different electrode materials with different charge storage mechanisms, such as combining an EDL electrode with a battery-type electrode. 11,12 For battery-type electrodes, materials such as transition metal oxides, hydroxides, nitrides, and sulfides as well as conductive polymers have been extensively investigated as potential candidates.…”