Low-cost Ni@C core-shell nanoparticles (NPs) were synthesized by means of the electrical explosion of wire method and were applied as a bifunctional catalyst for overall water splitting. XPS, HRTEM, and BET results revealed that the carbon shell effectively protects the metallic core from oxidation while providing a porous structure that yields a high surface area, which in turn enhances the catalytic activity. Through material analysis, we established a link between synthesis conditions and resulting morphology, electronic and crystal structure of the outer layers of Ni@C NPs. Thanks to the optimum morphology and favorable shell electronic structure, Ni@C(15%) showed superior catalytic activity. An electrolyzer based on bifunctional Ni@C(15%) required only 1.71 V of voltage to deliver 10 mA cm(-2). The overpotential for water splitting is 0.12 V lower than that for a Ni benchmark electrolyzer. A stable and scalable PV-electrolysis system for water splitting that is fully based on all-inorganic CIGS PV and Ni@C(15%) was constructed. Water splitting is driven at a high current of similar to 10 mA under the illumination of 100 mW cm(-2), corresponding to a solar-to-hydrogen (STH) efficiency of 8.14% with 11.65% efficiency of the sub-module at the operating point. The efficiency of the STH device can be increased up to 10% by increasing the operating current through a further decrease of the Ni@C(15%) catalyst overpotential by optimization of its electronic structure.