Designing Sn-based Catalysts For Electrochemical Reduction Of CO₂

The electroreduction of CO₂(CO₂RR)into highly value-added fuel,HCOOH,has been considered as a perfect approach to converse renewable energy and mitigate environmental crisis.Sn based materials are one of the promising candidates to electrocatalytically convert CO₂ to HCOOH.Unfortunately,Sn -based electrocatalysts usually suffer from over-high overpotential,poor selectivity,intense H₂ evolution reaction as well as poor durability,which seriously hinder their future development and application.The selectivity of HCOOH can be increased by an enlarged electrochemical surface area and an enhanced adsorption of CO₂^·-intermediate,which are decided by the electronic structure of electrocatalysts.Herein,we developed Sn -based composites to modify the electronic and geometric structure of Sn species.The ultimate goal is to improve the performance of CO₂RR with high current density and Faradaic efficiency together with long-time stability.Firstly,a electrocatalyst(Sn /CN)with Sn particle-decorated on polymeric carbon nitride(CN)was successfully developed via a facile approach reducing Sn²⁺by NaBH₄.The Sn species and CN substrate are bound together by strong chemical bonding,rendering the composite catalyst with a highly stable structure.The electronic structure of Sn catalyst has been well tailored as the electron transfer from N atoms of CN to Sn atoms.The modified Sn sites,rich with electrons,favor the adsorption and activation of CO₂,facilitate charge transport,improve the reaction kinetics.Finally,the efficiency of electrochemical conversion CO₂ to HCOOH was enhanced.The composite electrocatalyst demonstrates an excellent Faradaic efficiency of formic acid(FE_HCOOH)up to 96%at the potential of-0.9 V versus RHE,which remains at above 92%during the electrochemical reaction of 10 h.Sn quantum dots(Sn -QDs)incorporated polymeric carbon nitride(CN)electrocatalysts(Sn -QDs/CN)have been synthesized through in-situ electrochemical reduction.The as-obtained Sn -QDs were highly dispersed with high crystallinity and average size of 2-3 nm.The small particle size of Sn -QDs endowed the electrocatalyst with high electrochemical active surface area(ECSA),which was about 4.4 times that of Sn particles.And the CO₂RR kinetics has been accelerated by the decreased size.Sn -QDs/CN exhibited a high Faradaic efficiency of HCOOH and a good electrochemical durability.The FE_HCOOH on Sn -QDs/CN reached up to 95%at-1.0 V vs RHE.And,the Sn -QDs electrocatalyst exhibited a good electrochemical durability for 24 h.SnO₂/Bi₂O₃ oxide electrocatalysts were obtained hydrothermally.A built-in–potential at the interface of SnO₂/Bi₂O₃has been formed naturally by their different work functions.And an interfacial electron effect between SnO₂ and Bi₂O₃,that is,the interfacial electronic transfer from Bi₂O₃ to SnO₂,made SnO₂ rich of electrons.This promoted the adsorption/activation of CO₂ molecule and stabilized CO₂·^-intermediate,improved the charge separation as well as the kinetics of electron transfer in the composite electrocatalyst.DFT calculations revealed that the existence of Bi₂O₃ in SnO₂/Bi₂O₃ could favor the adsorption of HCOO*intermediate and suppress desorption of H*,as compared with pure SnO₂.As a result,the SnO₂/Bi₂O₃ catalyst achieved high performance on CO₂RR and suppressed HER.Moreover,the strong interfacial interaction in SnO₂/Bi₂O₃ protected active sites of SnO₂ from electrolytic reduction,making SnO₂ species highly stable during prolonged CO₂RR.