Homogeneous Electrocatalytic Hydrogen Evolution Of Nickel Based Or Copper Based Molecular Catalysts

With the arrival of the oil crisis,hydrogen?H₂?is considered as one of the ideal alternative for traditional fossil fuels.In many hydrogen production methods,the use of electrocatalytic hydrogen production can directly obtain pure hydrogen.According to the composition,molecular catalysts can be classified:non-noble metal and noble metal molecular catalysts.The reserves of noble metals are very rare,leding to high costs,which greatly limited the development and application of noble metal catalysts in the catalytic of hydrogen production.Therefore,it is necessary to develop new type,low-cost and highly efficient non-noble metal molecular catalyst.Based on the previous research work,this thesis constructs three highly efficient electrocatalytic hydrogen production systems based on copper and nickel molecular catalysts.?1?The use of those complexes as molecular catalysts in the field of electrocatalytic hydrogen production has rarely been reported.Therefore,the first system in this thesis synthesized two pyrazine copper molecular catalysts C1 and C2.The electrocatalytic hydrogen production TOF of these two catalysts in the acetonitrile solvent,triethylamine hydrochloride or acetic acid as proton source were 1750 s^-1,1033 s^-1 and1940 s^-1,1434 s^-1,respectively.The electrocatalytic hydrogen production efficiencies of C1 and C2 in DMF solvent(453 s^-1 and 859 s^-1,respectively)were greatly reduced.The reason is that DMF can form stable hydrogen bonds with N atoms not participating in coordination in the C1 and C2 structures,and the catalytic activities of C1 and C2are lowered.We combine the UV-Vis absorption spectroscopy titration experimental data that the catalytic hydrogen production pathway of C1 and C2 may be CECE.?2?Then we synthesized a bis-selenium pyrazine nickel molecular catalyst C3.In the acetonitrile solvent,triethylamine hydrochloride as a proton source,the electrocatalytic hydrogen production TOF of C3 is as high as 24311 s^-1.The electrocatalytic efficiency of C3 is significantly higher than that of hydrogenase(6000-9000 s^-1)in nature,and is much higher than most of the non-noble metal molecular catalysts reported.Combining the results of electrochemical tests and UV-Vis absorption spectroscopy,we speculate that the electrocatalytic hydrogen production CECE pathway is a possible mechanism.?3?Through electrocatalytic hydrogen production test,we found that the carboxyl-substituted thiosemicarbazone nickel molecular catalyst?C5?in the DMF solution,trifluoroacetic acid or p-toluenesulfonic acid as a proton source,shows electrocatalytic hydrogen production activity.Next,we synthesized a carboxyl-substituted zinc thiosemicarbazone complex?C6?.Under the similar conditions,C6 has no electrocatalytic hydrogen production effect.This initially demonstrates the key role of nickel in the catalytic process of such molecular catalysts.Each of the molecular catalysts studied above has good solubility in an organic solvent,but has poor solubility in an aqueous solution.Inspired by the research work of the predecessors,we deprotonated the C5 with sodium carbonate to obtain a water-soluble catalyst C7.Electrocatalytic performance tests showed that the overpotential of C7 in alkaline buffer solution was low,only 266 mV.This is one of the few molecular catalysts that have electrocatalytic hydrogen production performance in alkaline solutions.This provides a new idea for the construction of electrocatalytic hydrogen production systems in pure aqueous solutions.Combined with relevant literature,we believe that the ECEC pathway of C5 is a possible mechanism for hydrogen production.