## 2 Materials and Methods
### Instrumentation  
The thermal behavior of the obtained semiroduct was studied using synchronous (TGA/DSC) thermal analysis (SDT Q-600 thermal analyzer, TA Instruments, New Castle, DE, USA) in an air flow in the temperature range of 25-1000 \({}^{\circ}\)C (controlled heating was performed in Al2O3 microcrucibles at the rate of 10 \({}^{\circ}\)/min in air flow, the gas flow rate was 250 mL/min, and the sample mass was 8.911 mg).  
To record the Fourier transform infrared (FTIR) spectra of the powder, a suspension was prepared in nujol mull, which was then placed as a film between KBr glasses. Spectra were recorded in the wave number range of 350-4000 cm\({}^{-1}\) (signal accumulation time--15 s and resolution--1 cm\({}^{-1}\)) using an FTIR spectrometer InfraLUM FT-08 (Lumex, St. Petersburg, Russia).  
XRD analysis of the obtained powder was carried out using a D8 Advance diffractometer (Bruker, Bremen, Germany; CuK\(\alpha\) = 1.5418 A, Ni filter, E = 40 keV, I = 40 mA, 2\(\theta\) range--5\({}^{\circ}\)-80\({}^{\circ}\) and 30\({}^{\circ}\)-41\({}^{\circ}\), resolution--0.02\({}^{\circ}\), signal accumulation time at one point was 0.3 s and 2.0 s (in the case of powder analysis at 2\(\theta\) range--30\({}^{\circ}\)-41\({}^{\circ}\))). The average size of the coherent scattering region (CSR) was calculated using the Debye-Scherrer formula [53]:  
\[D=\frac{k\lambda}{\beta cos\theta}, \tag{1}\]  
with \(D\) being crystallite size, \(\lambda\) being X-ray wavelength, \(k\) being Scherrer's constant, \(\beta\) being the full width at half maximum, and \(\theta\) being the diffraction angle.  
The microstructures of the obtained nanopowder and the formed array of miniature planar nanostructures were studied using scanning electron microscopy (SEM; NVision-40, Carl Zeiss, Inc., Oberkochen, Germany). Elemental analysis and mapping of element distributions over the film surface were performed as part of SEM by using an EDX spectrometer INCA X-MAX 80 (Oxford Instruments, Abingdon, UK).  
The film applied to the surface of the nickel-plated steel substrate was also examined by atomic force microscopy (AFM). As a result of the performed measurements, the data on the film microstructure and its local electrophysical properties were obtained. For this purpose, a Solver Pro-M scanning probe microscope (NT-MDT, Zelenograd, Russia) and ETALON HA-HR probes (ScanSens, Bremen, Germany) with W\({}_{2}\)C+ conductive coating (tip curvature radius \(<\) 35 nm) in modes of semicontact AFM, Kelvin probe force microscopy (KPFM), and scanning capacitive microscopy (SCM) were used. The measurements were performed at ambient conditions.  
The electrochemical characteristics of the sample were investigated using a potentiostat-galvanostat P-40X equipped with an electrochemical impedance measurement module FRA-24M (Electrochemical Instruments, Chernogolovka, Russia) at room temperature (25 \({}^{\circ}\)C). The material printed on the surface of a nickel-plated steel substrate served as the working electrode, and Ag/AgCl and a graphite rod were used as the reference and counter electrodes, respectively. The mass of the active material was 2.5 \(\times\) 10\({}^{-5}\) g. The measurements were carried out by cyclic voltammetry (CVA), galvanostatic charge-discharge (GCD), and electrochemical impedance spectroscopy (EIS) in the electrolyte, which was an aqueous solution of KOH (c = 3 mol/L). The value of the areal specific capacitance (C\({}_{s}\), F/cm\({}^{2}\)) of the electrode material under study was calculated using the discharge curves measured using the three-electrode scheme according to the following formula [54]:  
\[\mathrm{C_{s}=(I\times\Delta t)/(S\times\Delta V)} \tag{2}\]  
where I is the discharge current (A), \(\Delta t\) is the discharge time (s), \(\Delta V\) is the discharge potential window, and S is the geometric area of the electrode (cm\({}^{2}\)).