Synthesis Of Atomic Level Active Site Catalysts For The Applications Of Photo/Electrochemical Energy Conversion

Accompanied with the progress of modern industry,the demand for energy is ever-increasing.The traditional energy supply manner which mainly relies on the burning of fossil fuels has brought negative feedbacks on the global environment,such as haze and global warming.The development of high efficiency and low-cost catalysts used for the storage and conversion of renewable clean energy is the key to realize the transformation of energy structure and tackle environmental pollution issues.On the basis of the maximum atomic utilization and unique catalytic performance of single atom catalysts(SACs),the introduction of another adjacent metal atom to form dual-atomic site catalysts(DACs)can largely broaden the practical application field of atomic level catalysts.In our research,starting from the understanding of single atoms,a series of carbon-based single atom catalysts have been designed and prepared for the highly efficient electrocatalysis and photocatalysis.Subsequent investigation by introducing a second metal atom to form dual atoms catalyst largely improved the catalytic performance of atomic level catalysts due to the interaction between adjacent metal atoms.Detailed research contents are as follows:(1)Mass production of a single-atom cobalt photocatalyst for highperformance visible-light photocatalytic CO2 reductionWe came up with a Co photocatalyst with isolated Co single atoms anchored on a commercial super conductive carbon black(Co-SA@SP-800)and employ it to effectively boost the photocatalytic CO2 reduction reaction(CO2RR).Large scale production of the Co-SA@SP-800 catalyst can be achieved by a simple and practical adsorption-pyrolysis method.The as-prepared Co-SA@SP-800 catalyst presents remarkable photoactivity and CO selectivity with a CO production yield of 1.64×104 μmol g-1 and a CO selectivity of 84.2%after 2 h of light illumination in a heterogeneous system,which significantly outperforms other reference samples and most of the other efficient photocatalysts reported recently toward the conversion of CO2.In situ diffuse reflectance infrared Fourier transform(DRIFT)spectroscopy was carried out to investigate the reaction intermediates during the photocatalytic CO2RR.Control experiments and theoretical calculations revealed that the isolated single atomic Co-N4 sites greatly lower the energy barrier for the desorption of CO*during CO2-to-CO conversion,while suppressing H2 evolution in the competing water splitting reaction.This work provides valuable new insights for rationally designing and synthesizing high-performance single atom catalysts for photocatalytic CO2 reduction with ease of large-scale production.(2)Constructing N-coordinated Co and Cu single-atomic-pair sites towards boosted CO2 photoreductionThe visible-light-driven photocatalytic reduction reaction of carbon dioxide to value-added fuels presents a feasible approach to curb anthropogenic CO2 emissions and mitigate the increasing energy crisis.However,developing photocatalysts with excellent performance still remains a great challenge in this field.Herein,Co,Cu and N co-doped carbon nanoparticles(Co1Cu1/NC)were fabricated through the pyrolysis of zeolitic imidazolate framework(ZIF-8)with Cu(NO3)2 adsorbed inside the cavities and CoTBPP decorated over the surface of ZIF.Spherical aberration-corrected high-angle annular dark-field scanning transmission electron microscopy and electron energy loss spectroscopy measurements disclose the dual-metal single-atomic nature of Co1Cu1/NC consisting of atomically dispersed Co-Cu pair sites on a nitrogen-doped carbon support.Extended X-ray absorption fine-structure analysis reveals the tetra-Ncoordinated nature of each metal in Co1Cu1/NC(N2-Co-N2-Cu-N2).For the purpose of comparative study,Co,N-and Cu,N-codoped carbon nanoparticles(Co1/NC and Cu1/NC)also with single atomic site nature have been fabricated following the same route.The as-prepared Co1Cu1/NC exhibits highly effective photocatalytic CO2-to-CO reduction with a considerably high CO-generating yield of 22.46 mmol g-1 and a CO selectivity of 83.4%after 2 h of visible-light irradiation.Experimental characterizations and in particular theoretical calculations disclose the close association of the remarkable CO2RR catalytic activity of Co1Cu1/NC with the synergetic effect of the Co-Cu atomic-pair sites,which facilitate the conversion of CO2 to CO via lowering the energy barrier for the formation of the*COOH intermediate.This work paves a new avenue for the rational design and construction of atomic-pair photocatalysts with boosted performance.(3)Single iron atoms coordinated to g-C3N4 on hierarchical porous N-doped carbon polyhedra as a high-performance electrocatalyst for the oxygen reduction reactionCatalysts composed of isolated single Fe atoms coordinated to graphitic carbon nitride(g-C3N4)dispersed on hierarchical porous N-doped carbon polyhedra(Fe-g-C3N4/HPNCPs)were successfully prepared.The optimized catalyst,Fe-gC3N4/HPNCP-0.8,showed excellent electrocatalytic activity for the oxygen reduction reaction under alkaline conditions with a half-wave potential of 0.902 V,significantly outperforming commercial Pt/C,as well as high durability.The high performance stems from the synergistic effect of the atomically dispersed Fe-N2 sites and the advantages of the hierarchical porous structure for promoting mass transport and improving the accessibility of the active sites.(4)A robust diatomic electrocatalyst with single atom Fe and Cu sites on Ndoped carbon for oxygen reduction reaction in both acidic and alkaline mediaCatalyst with atomically dispersed transition metals on N-doped carbon support is a class of prospective candidates to replace platinum-based catalysts for oxygen reduction reaction(ORR),but the lack of satisfactory activity and durability still limit their practical application.Herein,a diatomic site ORR electrocatalyst with atomically dispersed Fe and Cu species co-anchored on three-dimensional nitrogen-doped polyhedra carbon was successfully prepared through a facile cooperation of post-adsorption and two-step pyrolysis method.A series of advanced characterization techniques confirm the generation of Fe and Cu single atomic sites on the N-doped carbon via FesA-N4 and CuSA-N4 planar coordination(FeSACuSA/NC).Density functional theory(DFT)calculations revealed that the electronic configurations of Fe-N4 sites in FeSACuSA/NC have been regulated by the existing Cu-N4 sites,contributing significantly to the optimization of intermediates adsorption and acceleration of kinetics during ORR process.Attributing to the structural advantages of FeSA-N4&CuSA-N4 sites and highly porous carbon matrix,the FeSACuSA/NC catalyst exhibits excellent electrocatalytic ORR performance,which outperforms the FeSA/NC or CuSA/NC single atom counterparts and the benchmark Pt/C catalyst,with showing half-wave potentials(E1/2)of 0.86 V and 0.88 V versus reversible hydrogen electrode in 0.1 M HClO4 and 0.1 M KOH solutions as well as high durability.Moreover,FesACusA/NC-based zinc-air battery presents high peak power density and outstanding cycling stability.This study sheds light on the significance of atomic structure regulation in boosting ORR electrocatalysts and develops a promising way for constructing high-efficiency dual single atomic metal site catalysts for electrochemical devices.