Preparation Of Electrocatalyst Based On Chrome-Containing Leather Scraps And Its Water Decomposition Performance

Leather industry has played an unparalleled role in promoting the improvement of human living standards,but in the production process,it will also be accompanied by a large number of solid wastes,one of which is chromecontaining leather scraps produced in the process of leather shaving,which was once listed as hazardous wastes by the state.Although experts and scholars have made great efforts to study the application of green chrome-free tanning agents to replace chrome salts in leather making process in recent years,up to now,no chrome-free tanning agents that can completely replace chrome salts have been found,which means that the problem of chrome-containing leather waste will still exist for a long time.If the latter is not properly handled and transformed,it will limit the development of leather industry.On the other hand,people’s serious consumption of fossil fuels has caused environmental pollution and energy crisis.As a green renewable energy,hydrogen energy may help people solve this problem.Using water electrolysis technology and high-efficiency electrocatalyst can continuously produce high-purity hydrogen.Electrolysis of water is composed of hydrogen evolution reaction(HER)at cathode and oxygen evolution reaction(OER)at anode.Electrocatalysts with excellent performance can play a key role in electrolysis of water.Although traditional noble metal Pt based catalysts have excellent performance,their high cost limits their development.Therefore,it is imperative to develop electrocatalysts with high activity and low cost.In this work,chrome-containing shavings were used as raw materials and converted into electrocatalysts through chemical treatment,which not only eliminated the environmental pollution caused by chrome-containing shavings,but also provided a new reference for exploring the preparation of electrocatalysts with high performance and low cost.Specific research contents are as follows:(1)In this study,MIL-101(Cr)-CS was synthesized from chromiumcontaining sludge after extracting collagen from leather chromium scraps as chromium source.The result showed that 2 g chromium-containing sludge was mixed with 0.2 g terephthalic acid(BDC)in the ratio of 10:1,pH was adjusted to about 1 with dilute nitric acid,hydrothermal reaction was carried out at 220℃ for 12 h,and then the samples were obtained after impurity removal,centrifugation and drying.The results showed that the morphology of MIL-101(Cr)-CS synthesized from chromium-containing sludge was similar to that of MIL101(Cr)-HF prepared from chromium nitrate nonahydrate,and the former had higher specific surface area(2412 m2/g vs.1855 m2/g)and larger pore volume(1.83 cm3/g vs.1.22 cm3/g).(2)On the basis of the previous studies on the preparation of MIL-101(Cr)from the residual chromium-containing sludge after extracting collagen from leather chromium scraps,the catalyst with Cr2O3/NiO-X heterostructure was synthesized by impregnating MIL-101(Cr)-CS as catalyst precursor,adsorbing nickel(Ⅱ)acetylacetone and annealing at high temperature.The existence of Cr2O3/NiO-X heterostructure was successfully proved by XRD,TEM and XPS.The effects of nickel(Ⅱ)acetylacetone concentration and annealing temperature on the OER properties of Cr2O3/NiO-X heterostructure were studied in order to optimize the performance of the electrocatalyst.The optimum loading concentration of nickel(Ⅱ)acetylacetonate is 6 mg/mL,and the optimum annealing temperature is 800℃.Cr2O3/NiO-6 showed the highest catalytic activity in a series of prepared catalysts:the overpotential was only 320 mV when the current density reached 10 mA·cm-2,and remained stable after 10 hours of electrolysis at 10 mA·cm-2 current density.The experimental results and theoretical calculations show that the excellent catalytic performance is due to the heterostructure of the catalyst which adjusts the electron distribution and reduces the reaction energy barrier in the catalytic process,and the large specific surface area also provides more active sites for the reaction.(3)CN/Cr2O3/Ru-X was prepared by impregnation method loaded with Ru3+in different concentrations on chrome-containing leather shavings,and then calcined at high temperature in N2 atmosphere.Their structures were characterized and analyzed by XRD,TEM,HAADF-STEM,ICP-OES,XPS and XAS.Because there are a lot of carboxyl groups in chromium-containing leather shavings,ruthenium ions(Ru3+)can combine with carboxyl groups to form ruthenium carboxylic acid complexes,and CN/Cr2O3/Ru-X monatomic catalysts are formed after annealing at high temperature.The influence of Ru(Ⅲ)content on HER properties of CN/Cr2O3/Ru-X was studied.The experimental result showed that when the optimal loading concentration of Ru3+ is 1 mg/mL,the excellent hydrogen reduction performance of the catalyst is shown.The overpotential of CN/Cr2O3/Ru-1 is only 28 mV in 1.0 M KOH(current density is 10 mA·cm-2),84 mV in 1.0 M phosphate buffer solution,56 mV in 0.5 M H2SO4 solution,and the catalyst has ideal stability at 10 mA·cm-2 current density.