The electrochemical hydrogenation of HMF to BHMF is an elegant alternative to the conventional thermocatalytic route for the production of high-value-added chemicals from biomass resources. In virtue of the wide potential window with promising Faradic efficiency (FE) towards BHMF, Cu-based electrode has been in the center of investigation. However, its structure–activity relationship remains ambiguous and its intrinsic catalytic activity is still unsatisfactory. In this work, we develop a two-step oxidation–reduction strategy to reconstruct the surface atom arrangement of the Cu foam (CF). By combination of multiple quasi-situ/in-situ techniques and density functional theory (DFT) calculation, the critical factor that governs the reaction is demonstrated to be facet effect of the metallic Cu crystal: Cu(110) facet accounts for the most favorable surface with enhanced chemisorption with reactants and selective production of BHMF, while Cu(100) facet might trigger the accumulation of the by-product 5,5′-bis(hydroxymethy)hydrofurion (BHH). With the optimized composition of the facets on the reconstructed Cu(OH) 2 -ER/CF, the performance could be noticeably enhanced with a BHMF FE of 92.3% and HMF conversion of 98.5% at a potential of −0.15 V versus reversible hydrogen electrode (vs. RHE) in 0.1 M KOH solution. This work sheds light on the incomplete mechanistic puzzle for Cu-catalyzed electrochemical hydrogenation of HMF to BHMF, and provides a theoretical foundation for further precise design of highly efficient catalytic electrodes.
Graphical Volcano plots are highly effective for understanding catalyst mechanisms and rational designing high-performance catalysts, particularly across different metals. However, the understanding of the relationship between different metals and their reaction mechanisms in 5-Hydroxymethylfurfural (HMF) reduction reactions is still limited. In this study, we explore the Gibbs free diagram of HMF reduction reactions on different metal surfaces and construct a volcano plot that connects HMF adsorption energy with the energy barriers of the rate-determining step. This provides a deeper understanding of HMFRR. Our theoretical findings align well with experimental results. Furthermore, we selectively constructed an AgPb bimetal interface based on our volcano plot, which boosted the catalyst activity. DFT calculations revealed that the AgPb bimetal surface effectively adjusts HMF adsorption energy and reduces energy barriers, suggesting that rational designing bimetal catalysts based on volcano plots is efficient. 2,5-bis(hydroxymethyl)furan (BHMF) derived from 5-Hydroxymethylfurfural (HMF) through a hydrogenation process has extensive applications in the production of resins, polymers, and artificial fibers. However, screening out the candidate and then modulating the active site to optimize the catalyst for high yield of BHMF are currently insufficient. In this study, Gibbs free energy diagrams of the reduction of HMF on 13 metals were presented, along with the identification of the rate-determining step (RDS) with the highest reaction barrier for each metal. We attempted to construct a volcano plot for HMFRR reaction. Additionally, a strategy was proposed to adjust the reaction barriers of RDS by combining two appropriate metals. Further experiments confirmed that Pb with the lowest energy barrier exhibited the highest HMF conversion (BHMF selectivity) among single metals. The modified catalyst by doping Ag on Pb, further boosted the HMF conversion (BHMF selectivity) from 42.1 % (59.4 %) to 80.8 % (80.9 %), respectively. These results provide an approach to rationally design and construct the catalyst system for efficient conversion of HMF.
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