To date, batteries are the most widely used energy storage devices, fulfilling the requirements of different industrial and consumer applications. However, the efficient use of renewable energy sources and the emergence of wearable electronics has created the need for new requirements such as high-speed energy delivery, faster charge–discharge speeds, longer lifetimes, and reusability. This leads to the need for supercapacitors, which can be a good complement to batteries. However, one of their drawbacks is their lower energy storage capability, which has triggered worldwide research efforts to increase their energy density. With the introduction of novel nanostructured materials, hierarchical pore structures, hybrid devices combining these materials, and unconventional electrolytes, significant developments have been reported in the literature. This paper reviews the short history of the evolution of supercapacitors and the fundamental aspects of supercapacitors, positioning them among other energy-storage systems. The main electrochemical measurement methods used to characterize their energy storage features are discussed with a focus on their specific characteristics and limitations. High importance is given to the integral components of the supercapacitor cell, particularly to the electrode materials and the different types of electrolytes that determine the performance of the supercapacitor device (e.g., storage capability, power output, cycling stability). Current directions in the development of electrode materials, including carbonaceous forms, transition metal-based compounds, conducting polymers, and novel materials are discussed. The synergy between the electrode material and the current collector is a key factor, as well as the fine-tuning of the electrode material and electrolyte.

Amorphous electroless Ni-B coatings were deposited on steel substrates with different surface morphologies and B contents (6.5–8.64 wt.%) that could be changed by altering the temperature and the composition of the baths. The supercapacitive behavior of the coatings was evaluated by cyclic voltammetry and galvanostatic charge–discharge measurements, and it was found that Ni-B coatings had higher capacitance than pure electroless Ni or the bulk Ni plate. A close relationship was identified between the microstructure, the B content, and the capacitive behavior of the coatings. The presence of the B alloying element had the most significant effect in determining the capacitance, while the surface area and particle size also contributed to its increase. A surface-specific capacity of 31 mF/cm² was achieved by the coating containing the highest B content and largest AFM surface area. Furthermore, it was revealed that the particle size of the deposits was determined by the combined effect of the bath temperature and the B content under the applied experimental conditions. The obtained results indicate that Ni-B coatings are promising candidates for supercapacitive applications.

The protective coatings industry is expanding, offering significant improvements in abrasion and wear resistance, which are crucial for economic sustainability. Despite the advancements, there remains a research gap in understanding the tribological properties and surface morphologies of electroless Ni-P and Ni-B coatings. This study aims to fill this gap by characterizing the surface structures, friction coefficients, and wear properties of two types of Ni-P and one type of Ni-B coatings. Using a ceramic ball counterpart in an SRV5 tribometer, we compared the wear rates according to Archard’s and Liu’s models, adhering to the DIN 51834-1 standard. Scanning electron microscopy was employed to analyze the impact of surface structures on friction coefficients and wear factors. The results reveal significant differences in wear resistance and friction behaviour among the coatings, providing valuable insights for their application in various industries.

Electroless nickel–phosphorus (Ni–P) coatings were deposited on steel substrates for 20, 40, and 60 min to examine the effect of deposition time on their pseudocapacitive behavior in an alkaline electrolyte. The coatings were characterized by scanning electron microscopy (SEM/EDS), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), cyclic voltammetry (CV), galvanostatic charge–discharge (GCD), and electrochemical impedance spectroscopy (EIS). Although coating mass, thickness, and roughness increased monotonically with deposition time, the electrochemical response showed a pronounced maximum at 40 min. The 40 min coating exhibited the highest areal capacitance in both CV and GCD measurements, reaching 33.1 ± 1.8 mF cm⁻² at 10 mV s⁻¹ and 426.5 ± 9.8 mF cm⁻² at 5 mA cm⁻², whereas the 60 min coating showed substantially lower capacitance. SEM and AFM confirmed progressive nodular coarsening and increasing surface roughness with time, but these geometric parameters alone did not explain the non-monotonic capacitance trend. In contrast, XPS revealed that the 40 min coating possessed the highest surface Ni content, while prolonged deposition led to a more P-enriched outermost surface. EIS further showed that the 40 min coating had the most favorable local high-frequency interfacial response, whereas the 60 min coating exhibited the highest local polarization. The results demonstrate that the electrochemical performance of electroless Ni–P coatings is more closely associated with the composition and accessibility of the activated near-surface region than with coating thickness or roughness alone, and that 40 min represents an interfacial optimum under the applied deposition conditions.

In our study, supercapacitor electrodes were prepared by depositing electroless Ni-B coating on copper plates, followed by nitric acid etching. The composition and the micro- and phase structure of the coatings were investigated by ICP-OES, PFIB-SEM, and XRD techniques. The original pebble-like structure of the coating consists of 0.8–10 µm particles, with an X-ray amorphous phase structure. The surface morphology and porosity of the coating can be tuned simply by changing the etching time. The supercapacitive performance of the electrodes was evaluated by means of cyclic voltammetry, galvanostatic charge–discharge, and electrochemical impedance spectroscopy measurements. The capacitance of the coating was found to vary on the etching time according to a maximum function, allowing for the determination of an optimal duration to obtain a specific capacitance of 157 mF/cm² (at 0.5 A/g). An excellent charge storage retention of 178% was found after 5000 CV cycles at a scan rate of 50 mV/s owing to the evolved electrochemically active network on the surface of the electrode, indicating a long-term stable and reliable electrode.