Understanding The Valence State Dependent Electrochemical CO₂ Reduction Performance Of Copper Based Electrocatalyst

Electrochemical conversion of CO₂（CO₂RR）towards valuable carbon-based feedstocks by renewable electricity is a promising technology,which helps to alleviate the excessive CO₂ emissions and store excess electricity as chemical energy.Although copper-based catalyst can reduce CO₂ towards multicarbon products,the poor C₂₊product selectivity limits its wide applications.Prior theoretical and experimental studies have shown that the synergistic effect between Cu⁺and Cu⁰ benefits for the enhanced selectivity of C₂₊products.However,the stable presence of Cu⁺species under the harsh CO₂RR reducing conditions remains a huge challenge.Therefore,it is urgent to develop an efficient strategy of stabilizing Cu⁺in copper-based catalyst.In this thesis,we prepared hexagonal boron nitride（h-BN）nanosheet decorated cuprous oxide（Cu₂O）as high performance CO₂RR catalyst.The reduction mechanism of Cu⁺in the catalyst was thoroughly analyzed by investigating the CO₂RR performance and tracking the change of copper valence state during CO₂RR.In combination with operando technique and theoretical calculations,the underlying mechanism of the Cu⁺stability has been thoroughly elucidated,which provides basic guidance for developing effective strategy of stabilizing Cu⁺.The main contents are as follows:（1）We prepared h-BN nanosheet decorated Cu₂O nanocatalyst（Cu₂O-BN）.The introduced h-BN can effectively improve the selectivity of multicarbon products and enhance the stability of Cu⁺.Cu₂O-BN exhibited a remarkable C₂H₄/CO ratio,which is 1.60 times higher than that of unmodified Cu₂O at-1.4V vs reversible hydrogen electrode.In situ and ex situ characterizations confirmed that the Cu⁺of unmodified Cu₂O were completely reduced to metallic Cu⁰ within 10 mins reduction reaction,while the Cu⁺in Cu₂O-BN can be well-maintained for 2 h continuous test.（2）Based on experimental results and theoretical calculations,we proposed a reasonable mechanism of“electron reservoir”to explain the stability of Cu⁺in Cu₂O-BN catalyst.Experimental results revealed the existence of strong electronic interaction of between h-BN and Cu₂O.Theoretical calculations showed that the introduction of h-BN redistributes the electron state of O 2p orbitals,receives more electrons from Cu₂O and enhances the strength of Cu-O bonds,which consequently stabilizes Cu⁺sites in Cu₂O.We proposed that h-BN acts as an“electron reservoir”to store excess electrons to stabilize Cu⁺in Cu₂O-BN during the CO₂RR.Overall,the h-BN nanosheet has been introduced into Cu₂O to improve the stability of Cu⁺species and promotes the multi-carbon selectivity of copper-based catalyst.The proposed“electron reservoir”mechanism can be used as a feasible avenue for the design of advanced CO₂RR electrocatalysts with high Cu⁺stability.