IB Group Metal Based Nanostructures Designed For Energy Catalysis

At the core of biological metabolism is the conversion of carbon between different oxidation states to store and release energy and to synthesize functional molecules.Similarly,the recycling of carbon is the center of human industrial society’s metabolism.Whereas in natural biological metabolism,the CO₂ produced from cell respiration can be balanced by plant photosynthesis,the consumption of CO₂ is as of a yet a missing part of humanity’s"industrial metabolism".With the needs of the economic development of various countries,global energy consumption continues to rise,among which fossil fuels are still in the leading position in the energy system,and the environmental problems caused by this have become more and more deteriorated.Therefore,the development of new energy technologies is the theme of sustainable development in the world.Methanol can be obtained by distillation from lignocellulose,and is one of the green energy sources derived from plant fiber conversion.Direct methanol fuel cell（DMFC）has recently received extensive research attention owing to their high energy density,and low pollution.Metallic platinum（Pt）is widely believed to be the most efficient catalyst for methanol oxidation（MOR）in DMFC.However,apart from high cost,Pt-based materials are very susceptible to CO poisoning while the CO is the common methanol oxidation intermediate,which dramatically restricts its catalysis stability.Therefore,developing alternative Pt-based catalysts have been the focus of methanol oxidation research.Electrocatalytic carbon dioxide reduction（CO₂RR）can store intermittent renewable energy power in the chemical bonds of valuable chemicals,reducing the chemical industry’s dependence on fossil energy and providing a promising way to close the anthropogenic carbon cycle.The technical core of electrocatalytic CO₂RR is the design of the efficient catalyst.The key is to minimize the energy input and achieve the final product with high efficiency and high selectivity.Despite tremendous efforts and some notable progress that have been made,so far state-of-the-art CO₂RR catalysts are still not satisfactory in either term of activity,selectivity and stability.Group IB transition metals have a wide range of applications in the above two catalytic reactions.The catalytic reaction is closely correlated with the metal surface structure,electronic state,and chemical composition.Even the same metal-based catalysts with different structures,morphologies,sizes,and surface atomic arrangements can exhibit entirely different catalytic activities towards the same reaction.This article provides the following solutions to the subsistent problem of MOR and CO₂RR through the precise design of IB group metal nanostructures.The details are as follows:（1）Considering that Pt-based materials are susceptible to CO poisoning,we used a simple one-pot method to synthesize the defect-rich ultrathin octahedral bimetallic Au3Ag nanoframes,and elaborated its morphological evolution and formation mechanism.Extensive structural characterizations show that abundant crystal defects can lead to lowered atomic coordination and varied electronic states of the metal atoms.During electrocatalytic methanol oxidation,the Au3 Ag nanoframes show excellent performance,with a high specific activity of 3.38 mA cm^-2,3.9 times that of commercial Pt/C.More intriguingly,the kinetics of methanol oxidation on the Au3Ag nanoframes was found counter-intuitively promoted by CO,ascribable to the altered reaction pathway and enhanced OH^-co-adsorption on the defect-rich surfaces,which can be well understood from the d-band model and comprehensive density functional theory（DFT）simulations.（2）Since the nano-frame structure exhibits excellent activity in many catalytic reactions,different from the research mentioned above（1）,we report an aqueous synthesis system that obtains ultrathin cubic Ag₃Au bimetallic nanoframes with a yield of nearly 100%,and the surface is clean.Transmission electron microscopy（TEM）and scanning electron microscopy（SEM）shows the evolution trajectory alongside its morphological changes during the growth process.Spherical aberration-corrected transmission electron microscopy（Cs-TEM）results show that Ag₃Au nanocubes have abundant defect sites.These defect sites exhibit incredibly high activity in electrocatalytic CO₂,with CO selectivity as high as 97%,and maintaining the selectivity is not attenuated for at least 10 hours.（3）Herein,aiming to break the linear scaling relationship of intermediates binding and minimize the kinetic barrier of CO₂ reduction reactions（CO₂RR）,ternary Cu-Au/Ag nanoframes are fabricated to decouple the two pivotal functions of CO generation and C-C coupling,where the former is greatly promoted by the alloyed Ag/Au substrate and the latter is elegantly facilitated by the highly strained and positively charged Cu domains.Therefore,extraordinary Faradic efficiencies of 69±5%and 77±2%on C2H4 production in H^-cell and flow cell,respectively,are achieved with great electrocatalytic stability.In-situ IR and DFT calculations unveil two competing pathways for C2H4 generation,of which the direct CO dimerization is energetically favored.（4）Methane is not only an essential raw material for human production activities but also a potent greenhouse gas.Using renewable electricity as an energy input,the renewable methane obtained through electrocatalytic CO₂RR can realize the global carbon reduction plan.However,the CO₂RR selectivity of methane is still low at the commercially relevant current density(>100 mA cm^-2).In this paper,three Ag@Cu2O nano cells with different cavity sizes were synthesized.By adjusting the cavity size,the CO coverage and*H adsorption were effectively adjusted to control the CO₂RR catalytic reaction path.We achieved a methane Faraday efficiency of 74 ± 2%in the flow-cell and a partial current density of 178±5 mA cm^-2 under-1.2VRHE.