NiFe-based materials are state-of-the-art electrocatalysts for water oxidation at alkaline pH. Several strategies to improve their activity have been reported, amongst which Ru-incorporation has appeared as a suitable approach. In this work, three Ni based nanomaterials have been prepared through organometallic synthesis and surface-decorated with small (sub-nanometric) Ru clusters (Ru(L)@Ni-NW) or large (ca. 8 nm) Ru nanoparticles (Ru(H)@Ni-NW and Ru(HH)@Ni-NW). As model systems, Ru(L)@Ni-NW and Ru(H)@Ni-NW have been thoroughly characterized by a complementary set of advanced techniques, including atom probe tomography, X-ray absorption spectroscopy, X-ray photoelectron spectroscopy and high-angle annular dark-field scanning transmission electron microscopy. Our study reveals that Ru nanoparticles remain unstable under electrocatalytic oxygen evolution reaction (OER) conditions, leaching from the Ni based NW surface. In contrast, sub-nanometric Ru clusters remain stable on the Ni based NWs and modify the Ni oxidation states at the surface sites, outperforming the counterparts that contain no Ru or Ru nanoparticles. The spectroelectrochemical and DFT modelling results suggest the interaction between the Ru sub-nanometric clusters and the Ni sites as the origin of the stabilization of Ni at higher oxidation states, boosting the OER efficiency under both Fe-containing (unpurified electrolyte) and Fe-free (purified electrolyte) conditions.

Three different cathodic materials for the hydrogen evolution reaction (HER) consisting of Ru nanoparticles (NPs) supported onto a bare and two doped reduced graphene oxides (r-GO) have been studied. Ru NPs have been synthesized in situ by means of the organometallic approach in the presence of each reduced graphene support (bare (rGO), N-doped (NH2-rGO) and P-doped (P-rGO)). (HR)TEM, EDX, EA, ICP-OES, XPS, Raman and NMR techniques have been used to fully characterize the obtained rGO-supported Ru materials. These materials have been deposited onto a glassy carbon rotating disk electrode (GC-RDE) to assess their HER electrocatalytic activity at acidic pH. The results show that all three materials are stable under reductive conditions for at least 12 h, and that the heteroatom-doping of the graphene structure extremely increases the activity of the electrodes, especially for the case of Ru@P-rGO, where the overpotential at -10 mAcm-2 decreases to only 2 mV. Realistic (based on experimental compositional data) modeling of the three rGO supports combined with DFT computational analysis of the electronic and electrocatalytic properties of the hybrid nanocatalysts allows attributing the observed electrocatalytic performances to a combination of interrelated factors such as the distance of the Ru atoms to the dopped rGO support and the hydride content at the Ru NP surface.

Complexes [(mu-S2C2H4NHR)Fe-2(CO)(6)] (R = p-C6H4-OCO(CH2)(9)Br (3a); R = p-C6H4-OCO(CH2)(8)CH3 (3b)) were used as stabilizing agents in the synthesis of Ni@3 and Au@3 nanoparticles (NPs), which are the first reported stable metallic NPs decorated with [(mu-S2C2H4NHR)Fe-2(CO)(6)] moieties. Electrochemical analysis reveals that incorporating the hydrogenase mimic into the NPs lowers the overpotential and enhances proton reduction electrocatalytic activity in organic media. The NPs act similarly to the [Fe4S4] cluster in natural enzymes, functioning as an electron reservoir/relay.

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.

Ultra-small Ru NPs grown on biomass-derived bare/P-doped graphene supports yield efficient and durable electrocatalytic H 2 production from water.

A set of OER electrodes based on Co(OH)2 nanoparticles and carbon microfibers of tailored composition is reported, which allows extracting valuable insights on the influence of the metal-support interface in their electrocatalytic performance.

Four different cathodes for the hydrogen evolution reaction (HER) have been developed by the decoration of commercial carbon microfibers with Ru nanoparticles (Ru NPs). Two types of carbon fibers have been used: pristine, as‐received, carbon fibers (pCF) and carbon fibers modified by an oxidative treatment that led to the functionalization of their surface with carboxylic groups (fCF). The decoration of these CFs with Ru NPs has been performed by two different methodologies based on the organometallic approach: direct synthesis of Ru NPs on top of the CFs (in‐situ Ru NPs) or impregnation of the CFs with a colloidal solution of preformed Ru NPs stabilized with 4‐phenylpyridine (RuPP NPs; ex‐situ Ru NPs). The electrocatalytic performance of these four cathodes (ex‐situ RuPP@pCF and RuPP@fCF; in‐situ Ru@pCF and Ru@fCF) for the HER has been studied in acidic conditions. The results obtained show that both the nature of the NPs and of the carbon fibers play a key role on the stability and activity of the hybrid electrodes: ex‐situ prepared Ru NPs afford better activities at lower overpotentials and better stabilities than those formed in‐situ. Among the two ex‐situ systems, an enhancement of the stability with pCF is observed, that may arise from more effective π‐interactions between 4‐phenylpyridine ligand and the surface of these carbon fibers. This interaction is somehow disfavored with fCF due to the presence of the surface carboxylic groups.