Electrocatalytic water splitting represents grand promise for hydrogen fuel in modern energy equipment, and the design and fabrication of higher performance catalysts are at the central. Herein, we report the sequential phosphorus (P)-doping into ruthenium (Ru) nanoparticles (Ru-P/C) by thermal annealing of Ru nanoparticles in phosphine (PH₃) atmosphere and deposition of extremely low concentration of platinum (Pt) to obtain P-doped Ru-Pt alloy catalyst supported on carbon nanotubes (CNTs), which is denoted as (Ru-P)#Pt/C. The data by X-ray diffraction spectroscopy and transmission electron microscopy show that the Ru nanoparticles existed in the form of hexagonal close-packed (hcp) phase with low crystallinity. The results by high-resolution X-ray photoelectron spectroscopy indicate that Ru was mainly in metallic state, and Pt was slightly and positively charged, ascribing to the bonding with P atoms. This indicates that the highly diluted Pt atoms may be dispersed on the surface of Ru nanoparticles through Ru-P-Pt bonds. Accordingly, the as-prepared (Ru-P)#Pt/C alloy catalysts displayed excellent alkaline hydrogen evolution activity, revealing only 17 mV vs. RHE at a current density of 10 mA·cm^-2 and a Tafel slope value of 27 mV·dec^-1, superior to those of the controlled samples Ru-P/C and trace amount of Pt loaded P-doped CNTs (Pt/C-P). Density functional theory (DFT) calculation suggests that P-doping into Ru can enhance the adsorption of water molecules and the activation for water splitting, while the Pt site on Ru-Pt alloy can behave as the hydrogen desorption site. Thus, the superior performance of (Ru-P)#Pt/C alloy catalyst might be attributed to the synergistic effect of P-doped Ru sites and Pt sites, which significantly improves the alkaline hydrogen evolution reaction kinetics.

Deep eutectic solvents (DESs) have been reported as a type of solvent for the controllable synthesis of metal nanostructures. Interestingly, flower-like palladium (Pd) nanoparticles composed of staggered nanosheets and nanospheres are spontaneously transformed into three-dimensional (3D) network nanostructures in choline chloride-urea DESs using ascorbic acid as a reducing agent. Systematic studies have been carried out to explore the formation mechanism, in which DESs itself acts as a solvent and soft template for the formation of 3D flower-like network nanostructures (FNNs). The amounts of hexadecyl trimethyl ammonium bromide and sodium hydroxide also play a crucial role in the anisotropic growth and generation of Pd-FNNs. The low electrocatalytic performance of Pd is one of the major challenges hindering the commercial application of fuel cells. Whereas, the 3D Pd-FNNs with lower surface energy and abundant grain boundaries exhibited the enhanced electrocatalytic activity and stability toward formic acid oxidation, by which the mass activity and specific activity were 2.7 and 1.4 times higher than those of commercial Pd black catalyst, respectively. Therefore, the current strategy provides a feasible route for the synthesis of unique Pd-based nanostructures.

Exploiting highly active and non-noble metal bifunctional catalysts at large current density is significant for the advancement of water electrolysis. In this work, CeO₂ electronically structure modulated FeNi bimetallic composite porous nanosheets in-situ grown on nickel foam (NiFe₂O₄-Fe₂₄N₁₀-CeO₂/NF) is synthesized. Electrochemical experiments show that the NiFe₂O₄-Fe₂₄N₁₀-CeO₂/NF exhibited the outstanding activities toward both oxygen and hydrogen evolution reactions (OER and HER) (η₁₀₀₀ = 352 mV and η₁₀₀₀ = 429 mV, respectively). When assembled into a two-electrode system for overall water splitting (OWS), it only needs a low cell voltage of 1.81 V to drive 100 mA·cm^-2. And it can operate stably at ±500 mA·cm^-2 over 30 h toward OER, HER and OWS without significant activity changes. The reason could be assigned to the electronic modulating of CeO₂ on FeNi composite, which can boost the intrinsic activity and optimize the adsorption of reaction intermediates. Moreover, the porous nanosheets in-situ grown on NF could enhance the contact of active site with electrolyte and facilitate the gas release, thus improving its chemical and mechanical stabilities. This study highlights a novel approach to design bifunctional non-noble metal catalysts for water splitting at large current density.

Rational design and synthesis of non-precious-metal catalyst plays an important role in improving the activity and stability for oxygen reduction reaction (ORR) but remains a major challenge. In this work, we used a facile approach to synthesize iron nanoparticles encapsulated in nitrogen-doped porous carbon materials (Fe@N-C) from functionalized metal-organic frameworks (MOFs, MET-6). Embedding Fe nanoparticles into the carbon skeleton increases the graphitization degree and the proportion of graphitic N as well as promotes the formation of mesopores in the catalyst. The Fe@N-C-30 catalyst showed the excellent ORR activity in alkaline solutions (E₀ = 0.97 V vs. RHE, E_1/2 = 0.89 V vs. RHE). Moreover, the Fe@N-C-30 catalyst exhibited better methanol resistance and long-term stability when compared to commercial Pt/C. The superior ORR performance could be attributed to the combination of high electrochemical surface area, relative high portion of graphitic-N, unique porous structures and the synergistic effect between the encapsulated Fe particles and the N-doped carbon layer. This work provides a promising method to construct efficient non-precious-metal ORR catalyst through MOFs.