Hydrogen Production By Water Electrolysis Coordinated With The Electrocatalytic Value-added Conversion Of Glycerol

With the increasing energy demands and the increasingly serious environmental pollution,the development of sustainable energy has been paid more and more attention.As a kind of clean,pollution-free,high energy density and zero carbon renewable energy carrier,hydrogen(H₂)has attracted extensive attention in industry and scientific fields.Compared with the traditional fossil fuel reforming process,water electrolysis is a simple and efficient method for hydrogen production with low carbon emission,which has broad application prospects.Unfortunately,due to the high overpotentials of anodic oxygen evolution reaction(OER)and cathodic hydrogen evolution reaction(HER),traditional water splitting is limited by large energy consumption and high cost in practical application.OER,in particular,as a kinetic-sluggish process featuring a rather high theoretical potential of 1.23 V,is responsible for the extremely high potential input and overall energy consumption in the electrocatalytic H₂ production system.Moreover,the resulting product,oxygen(O₂),not only has low added-value,but may also mix with H₂ to form explosive mixtures.Therefore,it is of great importance of developing a noval electrocatalytic hydrogen production system with enhanced efficiency,lowered energy consumption,and high safety.Based on the above discussion,in this paper,a series of systems for electrocatalytic hydrogen production by water splitting coordinated with value-added conversion of glycerol has been developed using thermodynamically more favorable reaction of glycerol electro-oxidation instead of OER.Meanwhile,the corresponding electrocatalyst has been rationally designed and prepared,and the electrolysis conditions has been precisely adjusted and controlled,which effectively reduce the energy consumption required for electrocatalytic H₂ production system,and achieve the value-added conversion of cheap chemical(glycerol).The specific research contents are as follows:(1)Ni-Mo nitride nanoplates grown on carbon fiber cloth(Ni-Mo-N/CFC)has been prepared by a hydrothermal process followed by high temperature nitride treatment.When using Ni-Mo-N/CFC as catalysts for both glycerol electro-oxidation reaction(GOR)and HER in alkaline solution,the current density of 10 m A cm^-2 can be obtained at 1.30 V vs.RHE and-40 m V vs.RHE,respectively,showing excellent electrocatalytic activities of GOR and HER.Especially,when the Ni-Mo-N/CFC catalysts were assembled into a two-electrode system in the precense of glycerol,a quite low cell voltage of 1.36 V is needed to drive the electrolyzer at 10 m A cm^-2,which is 260 m V lower than that of the OER electrolyzer under the same conditions.In addition,the concurrent electrolytic H₂ and formate productions have been achieved in this work at Faraday efficiencies up to 99.7%and 95.0%,respectively.Isotope labeled study proves that the formation of formate is the result of the successive-stepped reaction of glycerol over a long period of time and the formate is formed from both the primary and secondary carbons of glycerol.(2)Platinum-gold alloy catalyst directly grown on nickel foam(Pt Au/NF)has been synthesized by one-step galvanic replacement method.By optimizing the synthesis and electrolysis conditions of the catalyst,the Pt Au/NF electrode shows excellent GOR performance in 1.0 mol L^-1 KOH solution containing 0.5 mol L^-1glycerol,featuring an anode potential of as low as 0.4 V vs.RHE required for GOR at a current density of 20 m A cm^-2.When using platinum-gold alloy as the catalyst to establish a co-electrolysis system of GOR and HER,the electrolyzer can achieve 10m A cm^-2 at the voltage of 0.49 V,which is 0.74 V lower than the theoretical voltage of1.23 V for water splitting,largely reducing the total energy consumption of electrocatalytic hydrogen production system.Moreover,this electrolysis system achieves the electro-synthesis of high value-added C3 products such as lactic acid,while producing hydrogen at the cathode,and the selectivity of lactic acid at the optimized potential is up to 68.2%,which significantly elevates the economic benefit of the whole electrocatalytic hydrogen production system.(3)?-Mn O₂ nanosheets anchored on carbon paper(Mn O₂/CP)with abundant oxygen vacancies has been prepared by an one-step electrodeposition method,and their electrocatalytic performance of electrocatalytic hydrogen production system assisted by glycerol oxidation has been examined in acid media.Using the Mn O₂/CP as the anode catalyst,a rather low potential of 1.36 V vs.RHE is required at the current density of 10 m A cm^-2 in acidic electrolyte containing glycerol,while comparatively 1.63 V is required for OER under the same conditions.Replacing OER with glycerol electro-oxidation under acidic conditions not only reduces the energy consumption of electrolysis,but also achieve the production of high value-added chemicals,such as formic acid.More attactively,this electrocatalytic hydrogen production device combining the manganese oxide as the catalyst and the electrooxidation of glycerol,shows an extremely high stability over 865 hours,while the OER-based electrolysis device lasts less than 10 hours.Moreover,the structural changes of the catalysts during the reaction process was observed by electrochemical in-situ Raman spectroscopy,and the intrinsic mechanism of glycerol enhancing catalyst durability was investigated by density functional theory(DFT)calculation.Additionally,this strategy has been extended to the electrocatalytic hydrogen productions assisted by the oxidations of other alcohols(such as ethylene glycol,1,2-propanediol,etc.),providing a new idea for the application of non-noble metal catalysts in the highly durable electrocatalytic hydrogen production system under acidic conditions.