Electrochemical H₂ Production Coupled With Gilcerol Selective Oxidation To Lactic Acid

The production of hydrogen（H₂）directly from water using electrochemical technology powered by renewable energy sources such as solar and wind is widely regarded as a green approach.However,at present,the electrolysis of aquatic hydrogen still faces the problem of high cost.Coupling organic oxidation with water electrolysis to produce hydrogen is a green synthetic way to produce hydrogen and high-value chemicals at the same time and reduce the cost of hydrogen production.Glycerol is a widely available and inexpensive basic raw material,which can be used to prepare various C₁-C₃products such as aldehydes,ketones,and acids through catalytic oxidation.Among them,lactic acid is one of the important products of glycerol oxidation,which is widely used in the preparation of biodegradable plastics（polylactic acid,polyester）,as well as green solvents and chemicals.At present,researchers have preliminarily realized the electrocatalytic oxidation of glycerol to lactic acid using precious metals（such as platinum and gold）as catalysts.However,this research field still faces problems such as low current density of glycerol oxidation,poor selectivity and low yield of lactic acid,which is difficult to meet the needs of industrial applications.With scientific problems above,this thesis focuses on hydrogen production by electrolysis of water coupling glycerin oxidation lactic acid is a research topic,with gold（Au）as the core catalyst,using metal doping and light auxiliary two strategies,realized the electric glycerin catalytic oxidation system improve the performance of lactic acid,and then use a variety of electrical characterization methods revealed glycerin catalytic oxidation reaction mechanism of lactic acid.The main research contents and conclusions are as follows:（1）Previous studies have proved that Au is one of the excellent catalysts for the oxidation of glycerol to lactic acid,but there are still problems such as slow reaction rate and low selectivity of lactic acid.In this paper,metal doping（alloying strategy）is proposed to improve the performance of electrocatalytic glycerol oxidation to lactic acid.Based on this idea,a variety of Au M bimetallic catalysts（M=Ag,Pt,Cu,Pd）were firstly prepared.Through the performance test and product analysis,it was proved that Au Ag catalyst had the best performance of electrocatalytic glycerol oxidation.Under the reaction voltage of 0.9 V vs.RHE,the glycerol conversion rate of Au₃Ag₁ catalyst reached 5.27mmol cm^-2 h^-1 in electrolyte containing 0.3 M glycerol and 3.0 M KOH,which was 3.45 times that of pure Au catalyst.In addition,the selectivity of lactic acid on Au₃Ag₁ catalyst reached 83.06%,and the yield was 81.53%,which is the highest value of electrocatalytic glycerol oxidation to produce lactic acid reported at present.The electrochemical surface area（ESCA）and glycerol conversion frequency（TOF）calculations showed that Ag itself had no activity for glycerol oxidation,and Ag doping mainly improved the intrinsic catalytic activity of Au（TOF value of Au₃Ag₁ catalyst increased about 4.5 times than that of pure Au）.In addition,it has been proved that Ag doping can make Au electron loss and positive valence,which is beneficial to promote the adsorption of glycerol on Au,thus improving the electrocatalytic oxidation activity of glycerol.（2）In order to improve the performance of electrocatalytic glycerol oxidation to lactic acid,in addition to the above metal doping strategy,we further proposed to use the local surface plasmon resonance（LSPR）effect of Au to improve the reaction rate of glycerol oxidation and the selectivity of lactic acid through the photoassisted strategy.Based on this idea,we first prepared Au nanowire catalyst by electrodeposition method,and used it for electrocatalytic glycerol oxidation to prepare lactic acid under light and dark conditions.The glycerol conversion rate of Au catalyst was 2.876 mmol cm^-2 h^-1 in electrolyte containing 0.3 M glycerol and 3.0 M KOH at 0.9 V vs.RHE reaction voltage,and under external light condition,which was 1.88 times of that of pure Au catalyst.The selectivity of lactic acid was 80.16%.By comparing with/without light performance at different temperatures and voltages,we demonstrate that photoassisted strategies can improve glycerol conversion rate and lactic acid selectivity at different temperatures and voltages（glycerol overoxidizes to produce more formic acid with the increase of voltage under dark conditions;The increase in temperature increases the selectivity of glyceric acid and subtartaric acid）.Finally,semi-in-situ Fourier transform infrared spectroscopy（FTIR）was used to demonstrate that light can promote the adsorption of Au to the secondary hydroxyl group of glycerol,thus increasing the reaction rate and lactic acid selectivity.