Progressive replacement of fossil fuels by sustainable and renewable energy sources is one of the most actual contemporary challenges. In this context, the solar-based electroconversion of water has become a valuable concept for production of an alternative fuel based on “green” hydrogen generation. Transition metal nanoparticles, such as nickel, are the benchmark catalysts for hydrogen evolution reaction, since they are highly active, stable and earth-abundant.

One of the emerging fields of solar energy harvesting is enhancing the catalytic reaction through the local surface plasmon resonance (LSPR) effect of the catalyst. Most studied mechanisms of the energy transfer from plasmonic nanoparticles are based on hot electron injection and plasmon-induced resonant energy transfer. However, the photothermal effect of the plasmon in transition metal nanoparticles is still often considered detrimental and is severely underestimated in the literature.

In this work, we have synthetized Ni nanoparticles with an elongated average shape by wetness impregnation of the hard silica template. The high distribution of sizes results in a broad plasmonic absorption in the visible range, which leads to a significant photothermal effect under solar illumination, reaching 93°C after 5 min under incident power of 0.5 W cm^-2.

Irradiation of the Ni-NPs cathode with concentrated solar light under HER cathodic conditions leads to the increase of the hydrogen production up to 27%. On the other side, by applying galvanostatic conditions to the electrode we were able to decrease the overpotential needed for the hydrogen formation by 185 mV with negligibly small overall heating of the cell.

Pulsed illumination has resulted a three-staged electrochemical response to the illumination, reflecting i) breaking of the nickel/electrolyte equilibrium towards adsorption predominance, ii) blocking of the active sites and iii) establishing of the new balance between the electronic and ionic subsystems. The transient study revealed two main processes in the mechanism of light-induced reaction enhancement at low current densities: i) enhanced electron transfer due to strong plasmonic heating and ii) thermal energy dissipation from the electrode to the electrolyte.

Based on the obtained results, we have shown that the illumination of the nanostructured nickel catalyst with solar light can lead to the enhanced HER rate, and, as a result, to improved hydrogen production. We expect the LSPR photothermal approach to pave way to a more efficient photoelectrochemical water splitting process, taking advantage of visible and near-IR illumination.