Integrating Electrooxidation Of Amines/Nitroalkanes With Electrocatalytic Hydrogen Evolution And Transfer Hydrogenation Of Nitroarenes

Hydrogen energy is one of the most potential clean energy in the future energy structure because of its advantages of high calorific value,no pollution,and wide application.The development of a cheap,efficient,and stable hydrogen production method is the key to realizing the development and utilization of hydrogen energy.Among many strategies,electrocatalytic hydrogen production from water splitting is considered to be the most promising one.However,the slow kinetics of oxygen evolution half-reaction seriously limits the overall energy efficiency and its large-scale industrial application.At the same time,the economic value of the generated oxygen is not high,and mixing oxygen with the generated hydrogen will bring a series of safety and subsequent separation problems.Therefore,it is of great significance to design and develop cheap and efficient catalysts,develop thermodynamics-favorable and high value-added organic oxidation reactions as an alternative for oxygen evolution reaction,and realize high-efficiency electrocatalytic hydrogen production from water electrolysis.In addition,using the active hydrogen atoms produced by water electrolysis as the hydrogen source is expected to realize the green and efficient hydrogenation of a series of organic compounds,which solves the problems of high cost,high toxicity,and dangerous operation of traditional hydrogenation.At present,there are few studies on unveiling the active species of oxygen evolution substitution reaction,and the law of material regulation of electrolytic water hydrogenation is still unclear.Therefore,this thesis developed a new type of organic oxidation instead of oxygen evolution reaction,studied its active species,constructed a coupling reaction system of hydrogen evolution/hydrogenation and organic oxidation,revealed the potential-regulation regulation mechanism for selective reduction of nitro compounds with water as a hydrogen source,and realized the paired electrosynthesis of high added value organic chemicals at both anode and cathode.The main contents are as follows:（1）Coupling a carbon-unchanged primary amine oxidation reaction as a new alternative anodic reaction with accelerating kinetics to produce value-added chemicals with hydrogen evolution as a low cell voltage was reported.NiSe nanowire arrays were used as a model anode catalyst.Diverse aromatic and aliphatic primary amines could be oxidized into corresponding nitriles with high yield and high selectivity.The yields of nitriles were as high as 93%with a Faraday efficiency of over 98%.Electrochemical in situ Raman spectra revealed that the Ni^III/Ni^IIredox mediator formed in situ on the surface of the NiSe electrode is an active species in the oxidation of primary amine.Then,the NiSe||CoP two-electrode system was constructed by coupling with the phosphide cathode with high hydrogen activity.When the current density reached 20m A cm^-2,the voltage required after adding 1mmol benzylamine was only 1.49 V,which was far lower than the voltage required for total water electrolysis（1.70 V）.The Faraday efficiencies of hydrogen evolution and benzylamine oxidation were 99%and98%respectively.These results showed that benzylamine oxidation coupled with hydrogen evolution could significantly reduce the cell voltage and improve the energy conversion efficiency.It is worth noting that the product nitrile after amine oxidation was hydrophobic and could be separated from the catalyst surface and floated on the electrolyte,which not only avoided the poisoning of the catalyst but also was conducive to the sustainable gram-scale production of the nitrile product.This study not only promoted the hydrogen evolution reaction and reduced the overall voltage,but also provided a green and simple method for the synthesis of nitriles.（2）Based on the selective oxidation of organic amines and the fundamental understanding of the mechanism of water splitting,a new system of coupling reductive hydrogenation of nitroaromatics with fatty amine oxidation with water as a hydrogen source was developed.Using high-efficiency active hydrogen CoP as the cathode and water as the hydrogen source,a series of azoxy-,azo-and amino-compounds with excellent selectivity,good functional group tolerance,and high yields are produced by applying different bias inputs.The synthetically significant and challenging asymmetric azoxy-aromatics could be controllably synthesized in moderate to good yields.The use of water as the hydrogen source made this strategy remarkably fascinating and promising.In addition,deuterated aromatic amines with a high deuterium content could be readily obtained by using D₂O.By pairing with anodic oxidation of aliphatic amines to nitriles,synthetically useful building blocks can be simultaneously produced in a CoP||Ni₂P two-electrode electrolyzer.Only 1.25 V was required to achieve a current density of 20 m A cm^-2,which was much lower than that of overall water splitting（1.70V）.The paired oxidation and reduction reactions could also be driven using a 1.5 V battery to synthesize nitrile and azoxybenzene with good yields and selectivity,further emphasizing the flexibility and controllability of our method.This work paved the way for a promising approach to the water-involved green synthesis of valuable chemicals through potential-controlled electrosynthesis.（3）On the basis of non-carburization reactions of the primary amine as an alternative anodic reaction,coupling a carburization oxidation reaction strategy with accelerating kinetics to produce value-added chemicals with hydrogen evolution as a low cell voltage was developed.Selecting the carburization reaction of electro oxidation ofα-nitrotoluene to E-（1-nitroethylene-1,2-diyl）dibenzene replacing the anodic oxygen evolution reaction as the model reaction.This low-cost NiSe cathode could deliver nitroethene with up to an E-type selectivity of 99%,a Faraday efficiency of 89%,and a reaction rate of 0.25 mmol cm^-2 h^-1.The high performance can be associated with its in situ formed Ni OOH surface layer and absorbed Se O_x^2-via Se leaching-oxidation during electrooxidation,and the preferential adsorption of two-NO₂groups of intermediate on Ni OOH.Based on the in situ and quasi in situ spectroscopic analyses of intermediates,we proposed the reaction mechanism of self-coupling of carbon radical and subsequent elimination of a nitrite molecule.In addition,this method exhibited good universality of various substrates.In the NiSe||NiSe two-electrode system,when the current density reached 10 m A cm^-2,the required voltage of nitrotoluene was only 1.36 V,saving 332 m V for total water electrolysis.Thus,this coupling system could significantly reduce the cell voltage and improved the added value of the product.This study not only provided a green preparation method for coupling E-nitroethene electrosynthsis with hydrogen production but also offered a new paradigm for designing materials to regulate the key steps of reaction and improve the selectivity of electrocatalytic products.