Electrochemical oxygen evolution reaction efficiently boosted by selective fluoridation of FeNi3 alloy/oxide hybrid

Performance boosting of hybrid metal oxide and metal alloy catalyst is crucial to the water electrolysis for hydrogen generation. Herein, a novel concept of selective fluoridation of metal alloy/oxide hybrid is proposed to boost their catalytic performance for the oxygen evolution reaction(OER). A well-recognized OER catalyst system of FeNi3 alloy/oxide embedded in nitrogen-doped porous nanofibers(FeNiO/NCF) is employed as a proof of concept, and it is selectively fluoridated by transforming the metal oxide to metal fluoride(FeNiF/NCF). The crystal structure and surface chemical state transformation are well supported by the spectroscopic analysis and the improved electrochemical performance for OER can be well correlated to the phase and structure change. Specifically, FeNiF/NCF can drive the benchmark current density of 10 mA cm-2 at 260 mV with a Tafel slope of 67 mV dec-1, about 70 mV less than that of FeNiO/NCF.Increased catalytic kinetics, rapid charge transfer ability, high catalytic efficiency and stability are also probed by electrochemical analysis. The high surface area and roughness are found mainly generated via the high-temperature annealing for the metal alloy/metal oxide formation, and the low-temperature fluoridation process intrinsically contributes to the active structure formation. It is an efficient and universal approach to increase the catalytic performance of metal alloy/oxide for energy-relevant catalytic reactions.

Core-shell heterostructure by coupling layered ReS_(2) with Co_(9)S_(8) nanocubes for boosted oxygen evolution reaction

The controllable morphology and composition of catalysts are crucial to improving the electrocatalytic activity of oxygen evolution reaction(OER).Herein,we construct a bimetallic heterostructure by sulfidation and hydrothermal methods,and the layered ReS_(2)is vertically aligned on Prussian blue-derived hollow Co_(9)S_(8)nanocubes(Co_(9)S_(8)@ReS_(2)).The core-shell structure of Co_(9)S_(8)@ReS_(2)can effectively prevent the restacking of layered ReS_(2),expose the abundant surface area and improve the utilization of electrocatalytic sites,resulting in fast electrolyte diffusion and charge transfer during OER.Due to the synergistic effect of the core-shell morphology and the formed bimetallic heterostructure,Co_(9)S_(8)@ReS_(2)exhibits excellent catalytic OER performance.At 10 mA/cm^(2),only 288 mV of overpotential is required with the Tafel slope of 73.3 mV/dec for Co_(9)S_(8)@ReS_(2),which are both lower than that of Co_(9)S_(8)and ReS_(2).Meanwhile,Co_(9)S_(8)@ReS_(2)exhibits high catalytic stability and low charge transfer resistance and the boosted active sites are confirmed by density functional theory.This work provides a rational design of the OER catalysts by constructing the bimetallic heterostructure.

Prussian blue analogue derived NiCoSe_(4) coupling with nitrogen-doped carbon nanofibers for pseudocapacitive electrodes

The design of pseudocapacitive materials by coupling transition metal compounds with a conductive carbon matrix is important for the high performance of supercapacitors.Herein,we construct the Prussian blue analogue derived nickel-cobalt selenides coupling with nitrogen-doped carbon nanofibers(NiCoSe_(4)-NCNFs)by carbonization and selenization of polyacrylonitrile nanofibers.The effect of selenization and element N doping on the morphological structure and surface chemistry of NiCoSe_(4)-NCNFs are evaluated.Due to the accelerated electrolyte ion diffusion,enlarged active surface area and the modified surface chemistry by the strong interaction at NiCoSe_(4)/NCNFs interfaces,NiCoSe_(4)-NCNFs show excellent capacitive behaviors in 1 mol/L KOH,and the specific capacitance is 1257 F/g at 1 A/g with a rate capability of 78%and cyclic stability of 82.9%.The Gibbs free energy of adsorption OH−is calculated by density functional theory to investigate the charge storage mechanism.This work offers a new strategy to construct the transition metal selenides/carbon nanofibers hybrids for high-performance supercapacitor devices.

Surface modulated hierarchical graphene film via sulfur and phosphorus dual-doping for high performance flexible supercapacitors

Graphene surface modification by heteroatom incorporation is an attractive strategy to construct flexible electrochemical capacitors.Herein,the steam-assistant heteroatoms of sulfur and phosphorus dualdoped graphene film(s-SPG)is fabricated via an ice-template and thermal-activation approach and they demonstrate an excellent pseudocapacitive behavior in flexible electrochemical capacitors.As probed by various microscopic and spectroscopic analysis,well-maintained porosity structure is formed during the freeze-drying and steam-activation treatment;the increased surface roughness is ascribed to heteroatoms doping by the formation of S-and P-containing functional groups as electrochemical active sites.A flexible device integrated by porous s-SPG film shows high pseudocapacitive behavior with high specific capacitance(169 F/g),rate capability(91.7%)and cyclic stability(92.5%).Even at the bend angle of 120,no obvious change of specific capacitance is found indicating a good flexibility of s-SPG devices;the current study shows that s-SPG is a very promising electrode to realize the practical applications of all solid flexible supercapacitors.

Surface oxidized iron-nickel nanorods anchoring on graphene architectures for oxygen evolution reaction

Surface oxidized iron-nickel nanorods coupling with reduced graphene architectures(FeNi-O-rGA)are successfully constructed via hydrothermal,freeze-drying,and thermal activation approaches.The hierarchical structure can provide lots of pathways for fast ion diffusion and charge transfer,and expose abundant catalytic sites.Meanwhile,the activity of FeNi-O-rGA is boosted by the optimized metal-oxygen bond strength in FeNi_(3)alloys.Partial oxidized FeNi nanorods are strongly coupled with rGA by the formation of metal-O-C bonds,which can impede the aggregation of FeNi_(3)alloys and increase the utilization of active sites.The special structure and partially oxidized FeNi nanorods for FeNi-O-rGA can result in excellent OER activity and catalytic stability.Only 215 mV of overpotential is required to drive the current density of 10 mA/cm^(2)as well as the Tafel slope of 50.9 mV/dec in 1 mol/L KOH.The change of surface chemistry of FeNi-O-rGA is confirmed by XPS after the OER test,which indicates the highly catalytic stability of FeNi-O-rGA due to the formation of intermediate metal oxyhydroxide.