Construction Of Highly Efficient Transition Metal Catalysts For Water Splitting

With the development of energy and environmental crisis,exploring an unpolluted and sustainable source is essential to alleviate human reliance on traditional fossil fuels.Besides,combining electrolytic water splitting with renewable resources,such as solar and wind energies,could largely contribute to the the preparation of hydrogen(H2)and green development.However,some problems have not been solved for H2 generation from water splitting,such as low catalytic efficiency,high catalytic cost,low catalytic stability and activity and so on.To address these issues,this doctoral paper has fully studied the high-efficiency heterogeneous water electrolysis catalysts from the insights of ligand effect,surface and interface construction,alloy effect,and size effect.The main points are as follows:1.From the point of view of multi-site synergistic catalysis,a universal room temperature impregnation strategy was proposed to prepare multi-site catalysts with atomic dispersion.Among them,Ru atomic dispersion catalyst shows excellent hydrogen evolution reaction(HER)under alkaline conditions.Mechanism analysis indicated that the single atom with Ru-C5 coordination structure can closely cooperate with Ru oxide cluster with Ru-O4 coordination configuration.In addition,based on ligand effect,osmium(Os)single atom catalysts with different coordination structures were also successfully synthesized by modifying carbon-based carriers with different heteroatoms.For example,Os-N3S1,Os-N4,Os-C4S2,Os-S6 and Os-C3 could be constructed.Besides,experiments and theoretical calculations showed that Os-N3S1 configuration single atoms can display best HER activity.Further mechanism analysis disclosed that coordination configurations of active sites could determine the corresponding oxidation state.Meanwhile,a"volcano diagram" relationship can be obtained between hydrogen evolution activity and the oxidation state of Os centers.2.IrCu nanowires with rich nanoislands was prepared by heterogeneous interface construction strategy,which illustrated excellent oxygen evolution(OER)and HER activity under non-acidic conditions.The mechanism analysis showed IrCu(111)/Ir(100)heterojunction on the surface of nanowires serves as an efficient catalytic active center because it contributes to the adsorption and decomposition of reactants.In addition,the non-noble metal CuNiS nanowires were also firstly prepared for alkali water splitting.This catalyst can solve the dependence of water electrolysis reaction on noble metals.Further analysis revealed that Ni3S2,NiS and so on were the real active species.3.Based on the alloy effect,defects-rich RhCu alloy nanotubes were successfully synthesized by multi-step wet chemical method.It is proved that RhCu nanotubes were obtained by etching RhCu nanowires from both ends.Meanwhile,RhCu alloy nanotubes can exhibit excellent HER and OER activities in wide pH conditions.Density functional theory(DFT)calculation reveals that Rh3Cu1 alloy phase is the main active center,which not only promotes the dissociation of water molecules,but also weakens the adsorption free energy of atomic oxygen and hydrogen.Besides,unique porous structure and surface defects(such as atomic defects and lattice distortion)can effectively promote electron transfer and adsorption of reaction intermediates.4.From insights of interface construction,amorphous RuCu nanosheets were grown on Cu nanotubes by template method.The obtained 3D RuCu nanocrystals contain numerous crystalline-amorphous interfaces,which displayed better hydrogen evolution activity than Pt/C under wide pH conditions.The combination of theory and experiment proved that Ru sites on the surface of nano sheets play as key role for water splitting.In addition,the synergistic effect of crystalline-amorphous interface can also greatly improve the reaction kinetics.