Conversion of sunlight into electricity or chemical fuels using catalysts is an important goal in chemistry. Many current research efforts focus on the development of novel catalysts based on abundant and inexpensive 3d transition metals.  In order to develop such systems towards commercial relevance, a better understanding of their reaction mechanisms is needed.

Here I present a Ni-centered hydrogen evolution catalyst and aim to resolve the catalytic reaction mechanism employing X-ray spectroscopic methods. The ligand-based redox chemistry occur upon reduction of LUMO orbital with π* character, which is highly distributed over the ligand. Although this orbital is capable of accumulating electrons and protons on the ligand, it is reduction of a LUMO with σ* character, results in H₂ production, thus highlighting the role of the σ* orbital reduction and possible formation of a Ni-hydride (Ni(III)-H).

I also present highly sensitive membrane inlet isotope-ratio mass spectrometry with online sampling to study the first turnover of the Co/M2P-oxide nanoparticles after a sudden jump in H₂¹⁸O enrichment. Mathematical modelling of the data reveals the basic mechanism of O–O bond formation, the number of Co centers per catalytic site for the production of the first O₂ molecule.