Strong electronic coupling of CoNi and N-doped-carbon for efficient urea-assisted H2 production at a large current density

Exploiting efficient urea oxidation reaction(UOR)and hydrogen evolution reaction(HER)catalysts are significant for energy-saving H2 production through urea-assisted water electrolysis,but it is still challenging.Herein,carbon-encapsulated CoNi coupled with CoNiMoO(CoNi@CN-CoNiMoO)is prepared by solvothermal method and calcination to enhance the activity/stability of urea-assisted water electrolysis at large current density.It exhibits good activity for UOR(E10/1,000=1.29/1.40 V)and HER(E-10/-1000=-45/-245 mV)in 1.0 M KOH+0.5 M urea solution.For the UOR||HER system,CoNi@CN-CoNiMoO only needs 1.58 V at 500 mA cm-2 and shows good stability.Density functional theory calculation suggests that the strong electronic interaction at the interface between NiCo alloy and N-doping-carbon layers can optimize the adsorption/desorption energy of UOR/HER intermediates and accelerate the water dissociation,which can expedite urea decomposition and Volmer step,thus increasing the UOR and HER activity,respectively.This work provides a new solution to design UOR/HER catalysts for H2 production through urea-assisted water electrolysis.

Electron modulation of cobalt carbonate hydroxide by Mo doping for urea-assisted hydrogen production

Combining urea oxidation reaction(UOR) with hydrogen evolution reaction(HER) is an effective method for energy saving and highly efficient electrocatalytic hydrogen production. Herein, molybdenumincorporated cobalt carbonate hydroxide nanoarrays(CoxMoyCH) are designed and synthesized as a bifunctional catalyst towards UOR and HER. Benefiting from the Mo doping, the dispersed nanoarray structure and redistributed electron density, the CoxMoyCH catalyst display outstanding catalytic performance and durability for both HER and UOR, affording the overpotential of 82 m V for HER and delivering a low potential of the 1.33 V for UOR(vs. reversible hydrogen electrode, RHE) to attain a current density of 10 m A cm^(-2), respectively. Remarkably, when CoxMoyCH was applied as bifunctional catalyst in a twoelectrode electrolyzer, a working voltage of 1.40 V is needed in urea-assisted water electrolysis at10 m A cm^(-2) and without apparent decline for 40 h, outperforming the working voltage of 1.51 V in conventional water electrolysis.

Synergistic Interfacial and Doping Engineering of Heterostructured NiCo(OH)_(x)-Co_(y)W as an Efficient Alkaline Hydrogen Evolution Electrocatalyst

To achieve high efficiency of water electrolysis to produce hydrogen(H_(2)),developing non-noble metal-based catalysts with consid-erable performance have been considered as a crucial strategy,which is correlated with both the interphase properties and multi-metal synergistic effects.Herein,as a proof of concept,a delicate NiCo(OH)_(x)-CoyW catalyst with a bush-like heterostructure was realized via gas-template-assisted electrodeposition,followed by an electrochemical etching-growth process,which ensured a high active area and fast gas release kinetics for a superior hydrogen evolution reaction,with an overpotential of 21 and 139 mV at 10 and 500 mA cm^(−2),respectively.Physical and electrochemical analyses demonstrated that the synergistic effect of the NiCo(OH)_(x)-Co_(y)W heteroge-neous interface resulted in favorable electron redistribution and faster electron transfer efficiency.The amorphous NiCo(OH)_(x) strengthened the water dissociation step,and metal phase of CoW provided sufficient sites for moderate H immediate adsorption/H_(2) desorption.In addition,NiCo(OH)_(x)-CoyW exhibited desirable urea oxidation reaction activity for matching H_(2) generation with a low voltage of 1.51 V at 50 mA cm^(−2).More importantly,the synthesis and testing of the NiCo(OH)_(x)-CoyW catalyst in this study were all solar-powered,sug-gesting a promising environmentally friendly process for practical applications.

Synthesis of porous carbon from orange peel waste for effective volatile organic compounds adsorption: role of typical components

Volatile organic compounds have posed a serious threat to the environment and human health,which require urgent and effective removal.In recent years,the preparation of porous carbon from biomass waste for volatile organic compounds adsorption has attracted increasing attention as a very cost-effective and promising technology.In this study,porous carbon was synthesized from orange peel by urea-assisted hydrothermal carbonization and KOH activation.The role of typical components(cellulose,hemicellulose,and lignin)in pore development and volatile organic compounds adsorption was investigated.Among the three components,hemicellulose was the major contributor to high porosity and abundant micropores in porous carbon.Higher hemicellulose content led to more abundant–COOR,amine-N,and pyrrolic/pyridonic-N in the derived hydrochar,which were favorable for porosity formation during activation.In this case,the toluene adsorption capacity of the porous carbon improved from 382.8 to 485.3 mg·g^(–1).Unlike hemicellulose,cellulose reduced the>C=O,amine-N,and pyrrolic/pyridonic-N content of the hydrochar,which caused porosity deterioration and worse toluene adsorption performance.Lignin bestowed the hydrochar with slightly increased–COOR,pyrrolic/pyridonic-N,and graphitic-N,and reduced>C=O,resulting in comparatively poor porosity and more abundant micropores.In general,the obtained porous carbon possessed abundant micropores and high specific surface area,with the highest up to 2882 m^(2)·g^(–1).This study can provide guidance for selecting suitable biomass waste to synthesize porous carbon with better porosity for efficient volatile organic compounds adsorption.

Enhanced ethanol sensing performance of N-doped ZnO derived from ZIF-8

Metal oxides derived from metal-organic framework(MOF) have attracted considerable attention due to its excellent performance and unique structure. Doping is considered as an effective method to improve gas-sensing performance. However, nonmetal doped metal oxides derived from MOF as gas-sensing materials have not been reported. Within this work, N atoms were successfully doped into the lattice of ZnO nanoparticles using ZIF-8 as a self-sacrificial template through a thermal treatment process with the assistant of urea. The obtained N-ZnO exhibited competitive ethanol-sensing performance, in which the response value of N-ZnO-5 to 100 ppm ethanol reached 115 at 190 ℃ with a satisfactory selectivity. It was found that the N-doping in ZnO facilitated the formation of oxygen vacancy that promoted the generation of adsorbed oxygen species to achieve the enhanced gas-sensing performance. Besides, the larger specific surface area resulting from the size reduction during the urea-assisted pyrolysis process can also be responsible for the improving of the ethanol-sensing performance.