Electrocatalytic Upcycling of Biomass and Plastic Wastes to Biodegradable Polymer Monomers and Hydrogen Fuel at High Current Densities

Abstract

Transformation of biomass and plastic wastes to value-added chemicals and fuels is considered an upcycling process that is beneficial to resource utilization. Electrocatalysis offers a sustainable approach; however, it remains a huge challenge to increase the current density and deliver market-demanded chemicals with high selectivity. Herein, we demonstrate an electrocatalytic strategy for upcycling glycerol (from biodiesel byproduct) to lactic acid and ethylene glycol (from polyethylene terephthalate waste) to glycolic acid, with both products being as valuable monomers for biodegradable polymer production. By using a nickel hydroxide-supported gold electrocatalyst (Au/Ni(OH)2), we achieve high selectivities of lactic acid and glycolic acid (77 and 91%, respectively) with high current densities at moderate potentials (317.7 mA/cm2 at 0.95 V vs RHE and 326.2 mA/cm2 at 1.15 V vs RHE, respectively). We reveal that glycerol and ethylene glycol can be enriched at the Au/Ni(OH)2 interface through their adjacent hydroxyl groups, substantially increasing local concentrations and thus high current densities. As a proof of concept, we employed a membrane-free flow electrolyzer for upcycling triglyceride and PET bottles, attaining 11.2 g of lactic acid coupled with 9.3 L of H2 and 13.7 g of glycolic acid coupled with 9.4 L of H2, respectively, revealing the potential of coproduction of valuable chemicals and H2 fuel from wastes in a sustainable fashion.

Photoassisted Strategy to Promote Glycerol Electrooxidation to Lactic Acid Coupled with Hydrogen Production

“…This indicates that C 1 and C 2 byproducts (including oxalic acid, glycolic acid, acetic acid, and formic acid) may be generated by the overoxidation of DHA/GLD intermediates via C−C bond cleavage. 25 According to these results and previous studies, 54 we deduce the reaction path in Figure 2g.…”

“…This phenomenon is hard to be explained through the photothermal effect alone because the increased temperature is adverse to LA selectivity. In our recent work, 54 we have calculated the Gibbs free energy diagrams of the GLY electrooxidation process over Au by the spin-polarized density functional theory (DFT). The results show that the electrooxidation of GLY to DHA (the key intermediate to form LA) over Au includes two elementary reactions with raised energy barriers: (i) the electron of the glycerol alkoxide group is extracted to the catalyst under an applied bias to form nucleophilic (HOCH 2 ) 2 CHO*; and (ii) electrophilic OH* is generated on Au (the rate-determining step (RDS)).…”

“…To the best of our knowledge, these high current densities at such low potentials overwhelm most of the previous reports for GLY electrooxidation in the literature (Figure b and Table S1). , − …”

Microwave-enhanced hydrogen production: a review

“…Plastics are rich sources of hydrogen, which makes them ideal for microwave-assisted catalytic upgrading to produce hydrogen once discarded; hence not only generating prots but also contributing to pollution reduction. [50][51][52][53][54] Typically, iron-, cobalt-, and nickel-based catalysts are the most commonly used for this recycling due to their ability to activate carbonhydrogen bonds. Specically, these catalysts are capable of selectively promoting the cleavage of carbon-hydrogen bonds to generate hydrogen.…”

Selective electro-reforming of waste polyethylene terephthalate-derived ethylene glycol into C2 chemicals with long-term stability

“…For example, recent works have reported that Au or Pd nanoparticles loaded on Ni(OH) 2 substrates can convert PET into glycolate. 24,25 Shi and co-workers achieved the production of value-added GA by using PdAg/NF as the anode electro-catalyst. 26 However, the performance of the catalyst is still far from satisfactory.…”