Enhancing the HER rate over Pt–TiO2 nanoparticles under controlled periodic illumination: role of light modulation

In hydrogen production through water splitting, two reactions are involved: the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), both with efficiency issues. In previous works, our group demonstrated the possibility of enhancing H2 production by conducting HCOOH photocatalytic reforming on metal-TiO2 nanoparticles under controlled periodic illumination (CPI) rather than continuous illumination performed at the same average incident photon flux. The enhancement was observed only over specific metals, including Pt, Pd and Rh, due to their low Tafel slopes. Hydrogen adsorption and desorption energies are strongly dependent on the potential at the metal nanoparticles, and we demonstrated the ability to use CPI to induce oscillations in the potential of the catalyst. In this work, by modulating the duty cycle and the frequency of the CPI, we observed both of these playing a key role in boosting HER. Experimental evidence suggest that the relaxation of the photopotential during the dark period is the key factor for increasing the photonic efficiency of the reaction.