Preparation Of Fe,S Doped Co-,Mo-Based Hydroxides And Their Electrocatalytic Water Splitting And Urea Oxidation

The non-renewability of fossil fuels and the environmental problems caused by the high rate of extraction in recent decades have made countries around the world re-examine the exploration and development of cleaner energy sources,and hydrogen energy has become the first choice for clean energy because of its high combustion value and no carbon pollution of combustion products.Electrocatalytic hydrogen production by hydrolysis is currently considered as one of the most effective methods.On the one hand,precious metal bases(platinum,ruthenium,iridium and their oxides)have been important catalysts in electrocatalytic hydrolysis reactions.However,the high cost and scarce resources greatly limit their large-scale commercial application.Currently,transition metal-based catalysts are one of the important catalytic materials to replace noble metal catalysts because of their relevance in terms of cost and stability.On the other hand,a large number of studies have shown that oxygen evolution reaction(OER),as the most important half-reaction for electrocatalytic hydrolysis,becomes a breakthrough for efficient reactions.In addition,the oxidation reaction of water substitution by anodic organic small molecules(urea),i.e.,urea oxidation reaction(UOR),can accelerate the anodic reaction and thus promote the cathodic hydrogen precipitation reaction.In view of this,this paper uses 3D nickel foam as a substrate and cobalt(molybdenum)based material as a template to enhance the OER and UOR reactions through internal electron regulation and atomic doping of Fe and S ions,and microscopic treatment of the template surface to achieve the promotion of the hydrogen precipitation reaction.Specific studies include:1.Needle-like cobalt-nickel hydroxide(CoNi-OH)nanoarrays grown on nickel foam were used as templates to grow ultrathin nanosheets by hydrothermal method to obtain layered thin-sheet-covered cobalt-nickel-iron-sulfur hydroxide(CoNiFeS-OH)nanoarrays.High resolution transmission microscope(HRTEM)showed the presence of amorphous/crystalline interface in CoNiFeS-OH,which could modify the electron transport and promote the electrocatalytic reaction.XPS characterization showed that CoNiFeS-OH is more favorable for Ni3+,Fe3+ and Co2+ formation,and they are beneficial to promote the adsorption of oxygen-containing intermediates in the OER process OER process.Furthermore,the addition of S ions improves the bonding between electrons at the periphery of metal particles,which significantly promotes the formation of CoNiFeS-OH and improves electron transport.Electrochemical tests showed that the layered sheet-covered CoNiFeS-OH nanoarrays had an OER overpotential of only 192 mV and a UOR potential of 1.329 V at a current density of 10 mA cm-2,and overall water splitting and urea electrolysis cell voltages of 1.571 V and 1.461 V,respectively.In addition,the CV cycling,multi-step chronoamperometry,chronoamperometry and chronopotentiometry tests showed that CoNiFeS-OH has excellent stability.2.Based on the above outstanding performance of Fe and S on the OER/UOR process,we envision the synthesis of a super-stable non-precious metal-based catalyst that is more adaptable to the industrial demand.Using zinc-cobalt bimetallic(oxygen)hydroxide(ZnCo-LDH)nanosheets as the precursor material,Fe and S elements were introduced to form a sheet-on-sheet on the surface of ZnCo-LDH nanosheets,making the zinc-cobalt-iron-sulfur hydroxide(ZnCoFeS-LDH)nanosheet array with a large reaction contact area.The OER test shows that a low overpotential of 202 mV is required to achieve 10 mA cm-2 current density;the UOR result shows that a low potential of 1.313 V can achieve a current density of 10 mA cm-2.In addition,the introduction of Zn elements to the overall structure stabilization mechanism makes ZnCoFeS-LDH exhibit excellent catalytic stability,and the chronoamperometry test shows that the catalytic activity remains unchanged after 48 h at a current density of 50 mA cm-2.3.To develop catalysts that can work stably at high current densities,arrays of molybdenum-iron(S-MoFe/NF)nanosheets with a morphology similar to the folded sulfur-doped head of a paper crane were grown directly on a 3D nickel foam skeleton by a one-step hydrothermal method.Based on the direct driving effect of the(oxygen)hydroxide species formed by Fe3+ ions on the OER process,this folded structure can better facilitate the adsorption and desorption of intermediates generated by the OER process during OER catalysis.In addition,the defects caused by the abnormal arrangement of atoms within the folded region are favorable to promote the OER process.The electrocatalytic test results showed that the overpotential of the paper crane-like S-MoFe/NF catalyst was 210 mV at a current density of 10 mA cm-2 and only 2 75 mV at a high current density of 200 mA cm-2.The results of the 20 h chronoamperometry test at a current density of 50 mA cm-2 showed excellent stability of the catalysts.