First-principles Study On The Charged Point Defects Tuned The Catalytic Performance Of Semiconductor

The shortage of fossil energy and severe environmental pollution have forced mankind to urgently explore alternatives to fossil energy and seek rich,environmentally friendly,renewable new energy.Solar energy is clean and abundant in reserves,but its utilization has problems of high cost and low conversion efficiency.Photocatalytic technology can directly utilize solar energy for water decomposition and can be used in the field of environmental pollution remediation;It can also reduce CO₂and slow down the greenhouse effect.On the other hand,highly active electrocatalysts for oxygen evolution reaction（OER）and oxygen reduction reaction（ORR）are crucial for energy conversion and storage.Therefore,designing semiconductor materials with high catalytic performance is of great significance for solving the problems of energy shortage and environmental pollution.In this paper,using first principles calculations based on density functional theory（DFT）,the catalytic properties of several semiconductor materials have been tuned using charged point defects.The following studies have been completed:（1）Using a hybrid density functional method,the formation energy,electronic structure,and electron carrier concentration（n₀）of Bi₂Mo O₆tuned by intrinsic point defects were studied.The results show that the easy formation of the+2 valence O vacancy(O_vac²⁺)is the reason for its intrinsic n-type conductivity under the condition of rich bismuth and poor oxygen,and O_vac²⁺with the very high concentration(up to 10¹⁹cm^-3)is the main defect in Bi₂Mo O₆;O_vac²⁺is favorable for photocatalytic activity;Under oxygen enriched conditions,the n₀after D⁺doping and quenching treatment is greater than 10¹⁷cm^-3;Moreover,under the broad range of chemical potentials,after quenching from 700 K to 300 K,Bi₂Mo O₆can be effectively donor-doped without significant compensation by intrinsic point defect formation,and n₀increases asΔμ_Odecreases or temperature increases.Therefore,by selecting oxygen deficient（bismuth rich）growth conditions and quenching at 700K to 300K,the formation of compensating acceptor defects can be suppressed,and this growth and quenching condition will achieve high n-type doping and suppression compensation.（2）Based on DFT,the theoretical study of 3d transition metal（TM=V,Cr,Mn,Fe,Co,Ni,Cu）doped g-C₃N₄was conducted,and the ORR/OER bifunctional activities of the neutral and charged states of the g-C₃N₄system were compared.The results show that 33 kinds of 3d TM doped g-C₃N₄are stable at different valence states.The+1 univalent Ni gap site(Ni_i¹⁺@C₅₄N₇₂)exhibits a low overpotential for both ORR（0.35 V）and OER（0.43 V）,and has a low formation energy within a certain Fermi level range,making it suitable for use in ORR/OER bifunctional catalysts;The ORR/OER activity of 3d TM doped g-C₃N₄is influenced not only by the previously thought Gibbs free energy（ΔG）,but also by the formation energy,charge state,and Fermi level position;Tuning the ORR/OER activity of TM doped g-C₃N₄with charged point defects will make it possible to optimize catalytic performance and develop potential electrocatalysts for renewable energy applications.（3）Using first principles,the stability,electronic structure,and optical properties of Bi OCl tuned by intrinsic defects and non-metallic（C,N,P,S,and F）doped point defects were investigated.The results show that:O_vac²⁺,Cl_vac¹⁺,O_Cl^1-,Bi_vac^3-F_O¹⁺and N_O^1-have the lowest formation energy under different chemical conditions,so they are easier to form;In order to achieve excellent n-type conductivity,Bi OCl point defect regulation should be carried out under bismuth rich and oxygen poor conditions;O_vac²⁺,O_Cl^1-,Bi_vac^3-,and N_O^1-defects narrow the band gap of Bi OCl.After O_vac²⁺,O_Cl^1-,Bi_vac^3-,and N_O^1-doping,the absorption coefficient in the visible light region increases;The O_vac²⁺defect have the narrowest band gap and the best optical absorption properties.This work has theoretical guiding significance for the study of charged point defects tuning the photocatalytic performance of BiOCl.