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Streszczenie:
For efficient alkaline water-splitting, it is crucial to have bifunctional electrocatalysts that exhibit low overpotentials, durability, and the possibility of being produced through scalable methods. This study involved the use of screen printing to apply a porous nickel microparticle/polymer interlayer onto commercial nickel foam, which then acted as a base for the solvothermal growth of cobalt-based oxide/hydroxide nanostructures. The optimized electrode showed excellent bifunctional capabilities in 1 M KOH, requiring only 61 mV for the hydrogen evolution reaction and 241 mV for the oxygen evolution reaction at a current density of 10 mA cm−2. In comparison, the control electrodes, such as those with cobalt directly deposited on unmodified nickel foam and screen-printed nickel foam substrates without cobalt, exhibited poorer overall performance. Although the cobalt-modified nickel foam exhibited a higher Cdl-derived apparent electrochemical surface area, the cobalt-modified screen-printed electrode achieved the best ECSA-normalized HER and OER responses, indicating that the enhancement in activity was not solely due to the capacitive surface area of the electrode. The increased integrated redox charge suggests a greater contribution from electrochemically accessible Co/Ni redox-active species, while impedance analysis supports a more favorable apparent interfacial response under the tested HER- and OER-relevant conditions. Long-term chronopotentiometry and post-stability SEM confirmed stable bifunctional operation.

Słowa kluczowe:
alkaline water splitting, bifunctional electrocatalyst, HER/OER, nickel foam, screen printing

Streszczenie:
The electrochemical performance of cobalt-based supercapacitor electrodes is often limited by the relatively smooth surface of pristine nickel foam substrates. To overcome this limitation, a microstructurally engineered nickel foam scaffold was fabricated by introducing a porous nickel microparticle interlayer via screen printing. Cobalt nanostructures were hydrothermally grown on the modified substrate, forming a hierarchical electrode (Co@NF-M), which was systematically compared with electrodes prepared on commercial nickel foam (Co@NF). Structural and spectroscopic analyses supported the formation of predominantly crystalline spinel Co3O4, characterized by mixed Co2 + /Co3+ oxidation states. Morphological analysis further demonstrated a porous cobalt nanostructure anchored onto a roughened nickel scaffold, providing abundant active sites and facilitating electrolyte penetration and ion diffusion. Electrochemical impedance spectroscopy indicated a reduced charge-transfer resistance and improved electron transport compared to the conventional Co@NF electrode. As a result, the Co@NF-M electrode exhibited superior electrochemical performance, delivering specific capacitances of 1278, 1184, 1003, and 602 F g−1 at 0.5, 1, 5, and 10 A g−1, respectively. Furthermore, the symmetric Co@NF-M//Co@NF-M device retained 95% of its initial capacitance after 3000 cycles, demonstrating excellent cycling stability. The enhanced performance is attributed to the engineered nickel scaffold, which promotes more uniform cobalt growth and improves interfacial contact while facilitating electron and ion transport.

Słowa kluczowe:
Cobalt oxide, Symmetric supercapacitor, Cycling stability, Tailored Nickel foam, Pseudocapacitor behavior