Ruthenium-nickel oxide derived from Ru-coupled Ni metal-organic framework for effective oxygen evolution reaction

Deciphering promotion of MoP over MoC in Pt catalysts for methanol-assisted water splitting reaction

Molybdenum-based compounds show promising promotion effects on Pt catalysts for energy-relevant catalysis reactions. Herein, a more effective promotion effect of MoP than MoC was found in assisting Pt nanoparticles for methanol-assisted hydrogen generation in light of the strong metal-support interaction and synergistic effect between Pt and MoP/C nanospheres. Electrochemical analyses and theoretical calculations demonstrated that Pt-MoP/C facilitated the oxidation and removal of CO intermediates more effectively than Pt-MoC/C. This enhanced performance was attributed to the distinct 6-coordination environment of hexagonal MoP and the elevated electron density of Mo induced by phosphorus. These structural and electronic features significantly enhanced electron transfer to Pt, thereby creating strong metal-support interaction and synergistic effect to improve the overall catalytic efficiency. Especially, the unique activities of Moδ+ and Moδ- in the MoP modified the surface structure of Pt, lowered the Pt d-band center, and optimized the local chemical state of Pt atoms, which resulted in more optimized adsorption energy and charge transfer capabilities of intermediates. The Pt-MoP/C electrolyzer thus showed both lower cell voltage than that of Pt-MoC/C and Pt/C electrolyzers in water splitting and methanol-assisted water splitting for hydrogen generation. This study offers insightful information about the promotion effect of molybdenum-based compounds in Pt catalyst systems in energy-relevant catalysis reactions.

In-situ stabilization of metal-nitride sites in sprouted 2D cMOF@LDHs hetero-nano petals on metaloxynitrides nanostems for enhanced water splitting

Addressing the challenges of enhancing water-splitting efficiency necessitates the exploration and rational design of high-performance and durable electrocatalysts with appealing nanoarchitectures. In this study, we present the design and fabrication of conjugated cMOF/LDH hetero-nano petals decorated with monodispersed Metal-N sites, which are uniformly shelled over tungsten oxynitride (WNO) nanowire arrays to form a unique core-shell architecture. For this rational engineering, WNO nanowire arrays were grown on carbon cloth. Then, a thin-layered Ru-Co-Fe layered double hydroxide (RuCoFe/LDH) was deposited around these wires, resulting in a highly porous three-dimensional array of hierarchical hetero RuCoFe-LDHs@WNO-NWs core-shell nanowires (RuCoFe-NSs@WNO-NWs). Subsequently, the linkers coordinated with the RuCoFe-LDH nanosheets and transformed them in-situ into the RuCoFe-cMOF nano petals (RuCoFe-NPs@WNO-NWs). Notably, the linker's amino groups functioned as hooks for precisely anchoring and stabilizing metal sites, forming the metal nitride (M-N) moieties. Interestingly, the designed bi-functional catalyst exhibited superior catalytic activities for both OER (230 mV @ 10 mAcm-2) and HER (49 mV @ 10 mAcm-2) in an alkaline medium. Additionally, an electrolyzer cell employing Ru-CoFe-NPs@WNO-NWs as a bi-functional electrocatalyst required 1.49V to reach a current density of 10 mA cm-2. These remarkable catalytic performances can be attributed to several key factors, including opulent exposed active sites, an efficient charge/mass transport pathway, an optimized electronic structure, and an interfacial synergy effect. Hence, this study provides a new perspective for the design of efficient bi-functional electrocatalysts for use in the energy related electrochemical devices.

Interface engineering of hierarchical flower-like N, P, O-doped NixPy self-supported electrodes for highly efficient water-to-hydrogen fuel/oxygen conversion

Rational construction of efficient bifunctional catalysts with robust catalytic activity and durability is significant for overall water splitting (conversion between water and hydrogen fuel/oxygen) using non-precious metal systems. In this work, the hierarchically porous N, P, O-doped transition metal phosphate in the Ni foam (NF) electrode (hollow flower-like NPO/NixPy@NF) was prepared through facile hydrothermal method coupled with phosphorization treatment. The hierarchical hollow flower-like NPO/NixPy@NF electrodes exhibited high bifunctional activity and stability for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in alkaline solutions. The optimized electrode showed low overpotentials of 76 and 240 mV for HER and OER to reach a current density of 10 mA cm-2, respectively. Notably, the NPO/NixPy@NF electrode only required a low voltage of 1.99 V to reach the current densities of 100 mA cm-2 with long-term stability for overall water splitting using the NPO/NixPy@NF|| NPO/NixPy@NF cell, surpassing that of the Pt/C-RuO2 (2.24 V@ 100 mA cm-2). The good catalytic and battery performance should be attributed to i) the open hierarchical structure that enhanced the mass transfer; ii) a highly conductive substrate that accelerated the electron transfer; iii) the rich heterojunction and strong synergy between Ni2P and Ni5P4 that improved the catalytic kinetic; iv) the proper-thickness amorphous phosphorus oxide nitride (PON) shell that realized the stability. This work demonstrates a promising methodology for designing bifunctional transition metal phosphides with high performance for efficient water splitting.

Hierarchically Structured Graphene Aerogel Supported Nickel-Cobalt Oxide Nanowires as an Efficient Electrocatalyst for Oxygen Evolution Reaction

The rational design of a heterostructure electrocatalyst is an attractive strategy to produce hydrogen energy by electrochemical water splitting. Herein, we have constructed hierarchically structured architectures by immobilizing nickel-cobalt oxide nanowires on/beneath the surface of reduced graphene aerogels (NiCoO2/rGAs) through solvent-thermal and activation treatments. The morphological structure of NiCoO2/rGAs was characterized by microscopic analysis, and the porous structure not only accelerates the electrolyte ion diffusion but also prevents the agglomeration of NiCoO2 nanowires, which is favorable to expose the large surface area and active sites. As further confirmed by the spectroscopic analysis, the tuned surface chemical state can boost the catalytic active sites to show the improved oxygen evolution reaction performance in alkaline electrolytes. Due to the synergistic effect of morphology and composition effect, NiCoO2/rGAs show the overpotential of 258 mV at the current density of 10 mA cm-2. Meanwhile, the small values of the Tafel slope and charge transfer resistance imply that NiCoO2/rGAs own fast kinetic behavior during the OER test. The overlap of CV curves at the initial and 1001st cycles and almost no change in current density after the chronoamperometric (CA) test for 10 h confirm that NiCoO2/rGAs own exceptional catalytic stability in a 1 M KOH electrolyte. This work provides a promising way to fabricate the hierarchically structured nanomaterials as efficient electrocatalysts for hydrogen production.