Analogously to enzymatic catalysis, where the active metal sites and their environment are controlled by protein residues, the catalytic properties of metal nanoparticles (NPs) can be tuned by carefully selecting their surface‐coordinated species. In artificial photosynthesis, surface‐functionalization emerged in the last decade, grounded on the development of reliable methods for tailored synthesis, advanced characterization and theoretical modeling of metal NPs, altogether with the aim of transferring to the nanoscale the mechanistic knowledge acquired from molecular complexes. Metal NPs surface‐functionalization modulates the energetics of key catalytic intermediates, introduces second coordination sphere effects, influences the catalyst‐electrolyte interface, and determines the metal NPs surface coverage and, accordingly, the number of accessible active sites. In photoactivated systems, metal NPs surface‐functionalization may play a key role in modulating the charge transfers and recombination processes between the light absorber and the active sites and in the light absorber itself. Thus, after a presentation of the most relevant synthetic methods to produce well‐defined surface‐functionalized metal NPs, a critical analysis of why the above effects are the cornerstone in enhancing their catalytic performance in the key processes of artificial photosynthesis, namely the oxygen evolution reaction, the hydrogen evolution reaction, and the CO₂ reduction reaction, is given.

A cobalt complex bearing a κ‐N₃P₂ ligand is presented (1⁺ or Co^I(L), where L is (1E,1′E)‐1,1′‐(pyridine‐2,6‐diyl)bis(N‐(3‐(diphenylphosphanyl)propyl)ethan‐1‐imine). Complex 1⁺ is stable under air at oxidation state Co^I thanks to the π‐acceptor character of the phosphine groups. Electrochemical behavior of 1⁺ reveals a two‐electron Co^I/Co^III oxidation process and an additional one‐electron reduction, which leads to an enhancement in the current due to hydrogen evolution reaction (HER) at E_onset=−1.6 V vs Fc/Fc⁺. In the presence of 1 equiv of bis(trifluoromethane)sulfonimide, 1⁺ forms the cobalt hydride derivative Co^III(L)‐H (2²⁺), which has been fully characterized. Further addition of 1 equiv of CoCp*₂ (Cp* is pentamethylcyclopentadienyl) affords the reduced Co^II(L)‐H (2⁺) species, which rapidly forms hydrogen and regenerates the initial Co^I(L) (1⁺). The spectroscopic characterization of catalytic intermediates together with DFT calculations support an unusual bimolecular homolytic mechanism in the catalytic HER with 1⁺.

The electrochemical reduction of organic contaminants allows their removal from water. In this contribution, the electrocatalytic hydrogenation of nitrobenzene is studied using both oxidized carbon fibres and ruthenium nanoparticles supported on unmodified carbon fibres as catalysts. The two systems produce azoxynitrobenzene as the main product, while aniline is only observed in minor quantities. Although PhNO₂ hydrogenation is the favoured reaction, the hydrogen evolution reaction (HER) competes in both systems under catalytic conditions. H₂ formation occurs in larger amounts when using the Ru nanoparticle based catalyst. While similar reaction outputs were observed for both catalytic systems, DFT calculations revealed some significant differences related to distinct interactions between the catalytic material and the organic substrates or products, which could pave the way for the design of new catalytic materials.