Combined Electrocatalytic Oxidation and Reduction to Selectively Cleave β‑O‑4 Linkage of Lignin over Platinum Electrode in Organic Solvent: Secondary Treatment Opportunity for CELF Process

Valorization of lignin is gaining popularity due to its ability to make industrial processes more sustainable. However, the currently prevalent catalytic technologies use large amounts of energy and harsh reaction conditions. As a result, bonds between lignin precursors are cleaved unselectively and the selectivity of aromatic products is reduced. An electrocatalytic approach may allow improved control, and few studies have assessed the electrocatalytic oxidation and reduction of lignin in organic solvents. Organic solvents like tetrahydrofuran (THF) are of interest for lignin electrocatalysis due to their use in the cosolvent-enhanced lignocellulosic fractionation (CELF) process. The CELF process has the ability to overcome biomass recalcitrance by breaking β-O-4 aryl ether interunit linkages. Using electrocatalytic conversion processes, additional β-O-4, interunit linkages can be broken down selectively. As a result, if these two processes are integrated, a high amount of phenolic hydroxyl groups with low-content aryl ether linkages will be produced, making the product suitable for the development of biofuels and other chemicals. This study shows that by using controlled electrocatalytic oxidation and reduction in THF/aqueous acidic electrolytes in the ratio of 2:1, nonpolar β-O-4 linkages can be cleaved. This ratio was chosen to mimic the electrolyte composition environment of the CELF pretreatment. The results from both attenuated total reflection-infrared spectroscopy (ATR-IR) and NMR characterization are consistent and show that β-O-4 interlinkage bonds were broken. Quantitative calculations from NMR show that during controlled oxidative potential holds (constant potential oxidation), the presence of aromatic structural components of the lignin polymer increased by 28.67% and aliphatic structural components decreased by 32.73%. On the other hand, during controlled reductive potential holds (constant potential reduction), the presence of aromatic structural compounds decreased by 33.50% and aliphatic structural compounds decreased by 78.43%. These results indicate that electrooxidation and electroreduction may be used strategically to cleave interunit linkages. Thus, if electrochemical degradation of lignin is used as a secondary treatment in conjunction with the CELF process, it will greatly increase the possibility of transforming lignin into value-added products

Cation Incorporation into Copper Oxide Lattice at Highly Oxidizing Potentials

Electrolyte cations can have significant effects on the kinetics and selectivity of electrocatalytic reactions. We show an atypical mechanism through which electrolyte cations can impact electrocatalyst performancedirect incorporation of the cation into the oxide electrocatalyst lattice. We investigate the transformations of copper electrodes in alkaline electrochemistry through operando X-ray absorption spectroscopy in KOH and Ba­(OH)2 electrolytes. In KOH electrolytes, both the near-edge structure and extended fine-structure agree with previous studies; however, the X-ray absorption spectra vary greatly in Ba­(OH)2 electrolytes. Through a combination of electronic structure modeling, near-edge simulation, and postreaction characterization, we propose that Ba2+ cations are directly incorporated into the lattice and form an ordered BaCuO2 phase at potentials more oxidizing than 200 mV vs the normal hydrogen electrode (NHE). BaCuO2 formation is followed by further oxidation to a bulk Cu3+-like BaxCuyOz phase at 900 mV vs NHE. Additionally, during reduction in Ba­(OH)2 electrolyte, we find both Cu–O bonds and Cu–Ba scattering persist at potentials as low as −400 mV vs NHE. To our knowledge, this is the first evidence for direct oxidative incorporation of an electrolyte cation into the bulk lattice to form a mixed oxide electrode. The oxidative incorporation of electrolyte cations to form mixed oxides could open a new route for the in situ formation of active and selective oxidation electrocatalysts