Promoting The Activity Of Ru(bda) Catalysts For The Water Oxidation With Electrostatic-Interaction

In the search for green and renewable energy,splitting water into hydrogen and oxygen is considered as one of the most desirable strategies.Compared with reduction of protons,the the overall water splitting reaction,due to the high energy barrier involved in the multiple proton-coupled electron transfers and the O-O bond formation.Therefore,the development of the water oxidation catalysts(WOCs)is highly desired.It has been found that ruthenium molecular catalysts have excellent catalytic performance for water oxidation,which attracts people’s attention.The Ru(bda)complexes were proposed to operate through a bimolecular mechanism(I2M).In order to improve the concentration of local catalysts in aqueous solution,we introduce the self-assembly of Ru(bda)molecules induced by electrostatic interaction into the field of water oxidation.This work uses cationic substituent(L1)and anionic substituent(L2)as axial ligands and negatively charged ligand 2,2′-bipyridine-6,6′-dicarboxylate as equatorial ligand to synthesize asymmetric complex 1a.The ~1H NMR,Cryo-TEM,SAXS and DLS were employed to identify the aggregation behavior of complex 1a.The calculations verified that the complex 1a with electrostatic interaction can favorably form the prereactive dimer.We found that there is also the electrostatic interaction between dication2a and dianion 3a in the mixture.The self-assembly behavior of the complex 2a and complex 3a in the mixed solution was demonstrated by the same experimental methods.The complex 1a,complex 2a,complex 3a and mixed solution(M1,[2a]:[3a]=1:1)were evaluated by chemical oxidation method.The catalytic activity of mixture M1 and complex 1a and is much better than the only 2a or 3a at the same concentration of ruthenium,indicating that both intermolecular and intramolecular electrostatic interactions can promote the catalytic water oxidation reaction.To further demonstrate that electrostatic interactions can enhance the catalytic activity of Ru(bda)complexes for water oxidation.Three similar systems were developed.In all of these systems,the asymmetric complexes 1b-1d and the mixtures M2-M4 exhibited much better catalytic activity than the symmetrical complexes with positive and negative charges.