(521ap) In-Situ Analysis of Electrocatalytic Conversion of 5-Hydroxymethylfurfural (HMF) By Scanning Electrochemical Microscopy (SECM)

5-hydroxymethylfurfural (HMF) is a biomass-derived feedstock and its derivatives can be used to produce plastics, chemicals, and liquid fuels. 2,5-furandicarboxylic acid (FDCA) and 2,5-diformylfuran (DFF) are oxidized derivatives of HMF, which can be served as precursors to synthesize bio-based polymers (i.e., polyethylene furanoate) and pharmaceuticals (i.e., macrocyclic ligands). Several thermochemical ways have been developed to selectively oxidize HMF, but those processes require harsh reaction conditions such as high oxygen pressure (> 2.5 bar) and elevated temperatures (> 100 °C) and often use toxic chemicals such as oxidizing agents. Compared to conventional thermochemical processes, electrochemical HMF oxidations have gathered attention as sustainable routes due to their mild operating conditions without toxic chemicals. Extensive research has been done on electrocatalytic oxidation of HMF in aqueous solutions. It has been known that the selectivity, yield, and faradaic efficiency of HMF oxidation largely depend on the pH of solutions and the composition of electrocatalysts. However, there is a lack of studying local pH near the electrocatalyst surfaces during the HMF oxidation reactions, which can affect kinetics and efficiency of the reactions. Herein, we aim to in-situ monitor the local pH during the heterogeneous electrocatalytic HMF oxidation processes and correlate their impact on electrocatalytic activities. Gold and copper were chosen as model electrocatalysts, served as substrate electrodes of scanning electrochemical microscope (SECM). Surface-functionalized tip electrode with pH-sensitive redox mediator (4-nitrothiophenol) displayed Nernstian shift in cyclic voltammogram, enabling detection of local pH in small gap between tip and substrate electrodes of SECM cells. In addition, selective detection of products of HMF oxidation at the tip electrode could distinguish electrocatalytic activities at the gold and copper electrocatalyst surfaces. The relationship between local pH and electrocatalytic activities established in this study would provide useful information for the design of electrochemical HMF oxidation processes with high selectivity and yield.