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.