Controlled Synthesis of Noble Metal Aerogels and Their Applications in Electrocatalysis and Surface-Enhanced Raman Scattering
Noble metal aerogels(NMAs)are an emerging class of porous materials that are entirely constructed by one or more kinds of nanostructured noble metals including gold(Au),silver(Ag),palladium(Pd),platinum(Pt),ruthenium(Ru),rhodium(Rh),osmium(Os),and iridium(Ir).They feature attributes of both nanostructured noble metals(e.g.,high catalytic activity,high electrical conductivity,and special optical properties)and aerogels(e.g.,self-standing architecture,large spe-cific surface area,abundant pores,and robust 3D networked structure).Therefore,since their discovery in 2009,NMAs have displayed tremendous potential in fields ranging from(electro)catalysis,battery electrodes,biosensing,plasmonic technolo-gies,and environment remediation.However,as young materials,the investigation of NMAs is far from sufficient.Controlled synthesis is the basis for new materials that dictate how far they can reach.The sol-gel behavior of the metal system is dis-tinct from that of conventional gel systems,thus requiring additional studies.However,the fundamental understanding of the fabrication process and thus the structure/composition control for NMAs are largely overlooked.In this context,our team has been focusing on developing effective fabrication strategies based on an in-depth understanding of the gelation mechanisms as well as the roles played by each component in the reaction.To this end,we have pioneered realizing ligament size control,unveiling the reductant chemistry,unlocking the ligand chemistry,and achieving minute-scale rapid gelation by coun-ter-intuitionally introducing force fields.We aim to eventually realize arbitrary manipulation of the composition and structure of NMAs,which is critical for paving the way for their further development.After gaining sufficient control capacity for NMAs,then we go for exploring their applications.It is crucial to select appropriate scenarios according to their unique at-tributes,so as to fully exert their potential and eventually find their disruptive application directions.Inheriting features of noble metals and aerogels,NMAs possess abundant catalytic/optical active sites,high electronic/mass transfer channels,and robust and self-supported networks.In this regard,they should be suited for the(photo)electrocatalysis and detection based on surface-enhanced Raman scattering(SERS).Indeed,numerous studies have demonstrated their exceptional electrocatalyt-ic performances towards diverse reactions such as the alcohol oxidation reaction(AOR),hydrogen evolution reaction(HER),oxygen evolution reaction(OER),oxygen reduction reaction(ORR),and carbon dioxide reduction reaction(CO2RR).We further pioneered incorporating light in the electrocatalytic process,opening the photoelectrocatalysis direction.Additionally,we found that Au aerogels can serve as ideal 3D SERS substrates for they feature hot spots across three dimensions,which enables their outstanding signal enhancement and misfocus tolerance.However,intentionally on-target performance optimi-zation and the exploration of new design perspectives for NMAs are still on the way.In this account,we summarize the rep-resentative endeavors made in controlled synthesis and electrocatalysis/SERS applications of NMAs.After a brief introduc-tion of NMAs,we will highlight the state-of-the-art understanding of the sol-gel process of metal systems,and how to achieve structure-controlled synthesis and rapid fabrication of NMAs.After narrating the progress in electrocatalysis and SERS applications,we will conclude the challenges and opportunities for these young materials.
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