Immobilizing Bimetallic RuCo Nanoalloys on Few-Layered MXene as a Robust Bifunctional Electrocatalyst for Overall Water Splitting.

Doping Co atoms into Ru lattices can tune the electronic structure of active sites, and the conductive MXene can adjust the electrical conductivity of catalysts, which are both favorable for improving the electrocatalytic activity of the catalyst for water splitting. Here, ruthenium-cobalt bimetallic nanoalloys coupled with exfoliated Ti3 C2 Tx MXene (RuCo-Ti3 C2 Tx ) have been constructed by ice-templated and thermal activation. Due to the strong interaction between the RuCo nanoalloys and conductive MXene, RuCo-Ti3 C2 Tx not only exhibits an excellent hydrogen evolution reaction (HER) performance with a low overpotential and Tafel slope (60 mV, 34.8 mV dec-1 in 0.5 M H2 SO4 and 52 mV, 38.7 mV dec-1 in 1 M KOH), but also good oxygen evolution reaction (OER) performance in an alkaline electrolyte (266 mV, 111.1 mV dec-1 in 1 M KOH). The assembled RuCo-Ti3 C2 Tx ||RuCo-Ti3 C2 Tx electrolyzer requires a lower potential (1.56 V) than does the Pt/C||RuO2 electrolyzer at 10 mA cm-2 . A boosted catalytic HER activity from immobilizing the RuCo nanoalloys on MXene was unveiled by density functional theory calculations. This study provides a feasible and efficient strategy for developing MXene-based catalysts for overall water splitting.

Hierarchical Architectures Based on Ru Nanoparticles/Oxygen-Rich-Carbon Nanotubes for Efficient Hydrogen Evolution.

Highly active and durable electrocatalysts are essential for producing hydrogen fuel through the hydrogen evolution reaction (HER). Here, a uniform deposition of Ru nanoparticles strongly interacting with oxygen-rich carbon nanotube architectures (Ru-OCNT) through ozonation and hydrothermal approaches has been designed. The hierarchical structure of Ru-OCNT is made by self-assembly of oxygen functionalities of OCNT. Ru nanoparticles interact strongly with OCNT at the Ru/OCNT interface to give excellent catalytic activity and stability of the Ru-OCNT, as further confirmed by density functional theory. Owing to the hierarchical structure and adjusted surface chemistry, Ru-OCNT has an overpotential of 34 mV at 10 mA cm-2 with a Tafel slope of 27.8 mV dec-1 in 1 M KOH, and an overpotential of 55 mV with Tafel slope of 33 mV dec-1 in 0.5 M H2 SO4 . The smaller Tafel slope of Ru-OCNT than Ru-CNT and commercial Pt/C in both alkaline and acidic electrolytes indicates high catalytic activity and fast charge transfer kinetics. The as-proposed chemistry provides the rational design of hierarchically structured CNT/nanoparticle electrocatalysts for HER to produce hydrogen fuel.

Interfacial Design of Ti3C2Tx MXene/Graphene Heterostructures Boosted Ru Nanoclusters with High Activity Toward Hydrogen Evolution Reaction.

The development of a cost-competitive and efficient electrocatalyst is both attractive and challenging for hydrogen production by hydrogen evolution reaction (HER). Herein, a facile glycol reduction method to construct Ru nanoclusters coupled with hierarchical exfoliated-MXene/reduced graphene oxide architectures (Ru-E-MXene/rGA) is reported. The hierarchical structure, formed by the self-assembly of graphene oxides, can effectively prohibit the self-stacking of MXene nanosheets. Meanwhile, the formation of the MXene/rGA interface can strongly trap the Ru3+ ions, resulting in the uniform distribution of Ru nanoclusters within Ru-E-MXene/rGA. The boosted catalytic activity and underlying catalytic mechanism during the HER process are proved by density functional theory. Ru-E-MXene/rGA exhibits overpotentials of 42 and 62 mV at 10 mA cm-2 in alkaline and acidic electrolytes, respectively. The small Tafel slope and charge transfer resistance (Rct) values elucidate its fast dynamic behavior. The cyclic voltammetry (CV) curves and chronoamperometry test confirm the high stability of Ru-E-MXene/rGA. These results demonstrate that coupling Ru nanoclusters with the MXene/rGA heterostructure represents an efficient strategy for constructing MXene-based catalysts with enhanced HER activity.

Boosting the Oxygen Evolution Reaction by Controllably Constructing FeNi3/C Nanorods.

Transition bimetallic alloy-based catalysts are regarded as attractive alternatives for the oxygen evolution reaction (OER), attributed to their competitive economics, high conductivity and intrinsic properties. Herein, we prepared FeNi3/C nanorods with largely improved catalytic OER activity by combining hydrothermal reaction and thermal annealing treatment. The temperature effect on the crystal structure and chemical composition of the FeNi3/C nanorods was revealed, and the enhanced catalytic performance of FeNi3/C with an annealing temperature of 400 °C was confirmed by several electrochemical tests. The outstanding catalytic performance was assigned to the formation of bimetallic alloys/carbon composites. The FeNi3/C nanorods showed an overpotential of 250 mV to afford a current density of 10 mA cm-2 and a Tafel slope of 84.9 mV dec-1, which were both smaller than the other control samples and commercial IrO2 catalysts. The fast kinetics and high catalytic stability were also verified by electrochemical impendence spectroscopy and chronoamperometry for 15 h. This study is favorable for the design and construction of bimetallic alloy-based materials as efficient catalysts for the OER.

Fluoridated Iron-Nickel Layered Double Hydroxide for Enhanced Performance in the Oxygen Evolution Reaction.

Layered double hydroxides (LDHs) are very promising but still far from satisfactory for catalyzing the electrochemical oxygen evolution reaction (OER) in water electrolysis. Herein, it was found that the catalytic performance of iron-nickel LDHs for OER can be largely boosted by a facile and controllable fluoridation approach at low temperatures. Temperature dependence of the crystal structure and surface chemical state was observed for the simple fluoridation of the iron-nickel LDH. However, no significant surface roughness and electrochemical active surface area increases were found, which was probably owing to the structure change from nanosheets to nanorods. Significant improvements in the performance, including the catalytic activity, stability, efficiency, and kinetics, were found compared with the pristine iron-nickel LDH. Specifically, iron-nickel fluoride obtained at 250 °C afforded the lowest overpotential of 225 mV (no iR correction) to drive 10 mA cm-2 loaded on an inert glassy carbon electrode with a small Tafel slope of 79 mV dec-1 , outperforming the noble-metal IrO2 catalyst and most of the similar Fe-Ni based catalysts. The performance improvement could be mainly attributed to the phase-structure transfer from metal-O bonding in the FeNi-LDHs to metal-F bonding after fluoridation, which means it is easier to form the real active sites of Fe-doped high-valence Ni-(oxy)hydroxide over the iron-nickel fluoride surface.

Ultrathin TiO2/BiVO4 nanosheet heterojunction arrays modified with NiFe-LDH nanoparticles for enhanced photoelectrochemical oxidation of water.

Herein, we have constructed NiFe-LDH nanoparticles modified ultrathin TiO2/BiVO4 nanosheet heterojunction arrays and explored the effects of different NiFe-LDH loading amount on photoelectrochemical water oxidation performance. The photocurrent of as-prepared TiO2/BiVO4/NiFe-LDH photoanode is about 2.5 times than that of TiO2/BiVO4, which is ascribed to the synergistic effect of heterojunction and co-catalyst. The heterojunction between TiO2 and BiVO4 suppresses the recombination of photogenerated electron-hole pairs effectively and the co-catalyst of NiFe-LDH accelerates the surface water oxidation reaction kinetics.