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Electrocatalytic upgrading of biomass-derived feedstocks driven by renewable electricity offers a greener way to reduce the global carbon footprint associated with the production of value-added chemicals. Paired electrolysis is an emerging platform for cogenerating high-valued chemicals from both the cathode and anode, potentially powered by renewable electricity from wind or solar sources. By pairing with an anodic biomass oxidation upgrading reaction, the elimination of the sluggish and less valuable water oxidation increases flow cell productivity and efficiency. In this presentation, we report our research progress on paired electrolsysis of HMF to production of higher valued chemicals in electrochemical flow cells. We first prepared an oxide-derived Ag (OD-Ag) electrode with high activity and up to 98.2% selectivity for the ECH of 5-(hydroxymethyl)furfural (HMF) to 2,5-bis(hydroxymethyl)furan (BHMF), and such efficient conversion was achieved in a three-electrode flow cell. The excellent BHMF selectivity was maintained over a broad potential range with long-term operational stability. In HMF-to-BHMF paired with 2,2,6,6-tetramethylpiperidine 1-oxyl (TEMPO)-mediated HMF-to-FDCA conversion, a markedly reduced cell voltage from ~7.5 V to ~2.0 V was observed by transferring the electrolysis from the H-type cell to the flow cell, corresponding to more than four-fold increase in energy efficiency in operation at 10 mA. A combined faradaic efficiency of 163% was obtained to BHMF and FDCA. Alternatively, the anodic hydrogen oxidation reaction on platinum further reduced the cell voltage to only ~0.85 V at 10 mA. Next, we have demonstrated membrane electrode assembly (MEA)-based flow cells for the paired electrolysis of 5-(hydroxymethyl)furfural (HMF) paired electrolysis to bis(hydroxymethyl)furan (BHMF) and 2,5-furandicarboxylic acid (FDCA). In this work, the oxygen evolution reaction (OER) was substituted by TEMPO-mediated HMF oxidation, dropping the cell voltage was from 1.4 V to 0.7 V at a current density of 1.0 mA cm−2. A minimized cell voltage of ~1.5 V for a continuous 24 h co-electrolysis of HMF was then achieved at the current density of 2 mA cm−2(constant current of 10 mA), leading to the highest combined faradaic efficiency (FE) of 139% for HMF-to-BHMF and HMF-to-FDCA. A NiFe oxide catalyst on carbon cloth further replaced the anodic TEMPO mediator for HMF paired electrolysis in a pH-asymmetric flow cell. We envision renewable electrical energy can potentially drive the whole process, thus providing a sustainable avenue towards distributed, scalable, and energy-efficient electrosynthesis.
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Valorization of Glycerol Through 2,2,6,6‐Tetramethyl‐1‐Piperidine‐N‐Oxyl (TEMPO)‐Catalyzed Electrochemical Oxidation with High C3 Product Selectivity: Impact of Stirred Bulk Versus Flow Electrolysis
Conversion of glycerol to value‐added products is an attractive solution to the oversupply of this byproduct of biofuel production. The glycerol oxidation reaction (GOR) may form product mixtures derived from the scission of the three‐carbon (C3) glycerol backbone, generating one‐ (C1) or two‐carbon (C2) species. Here, the bulk and flow electrolysis (FE) of the 2,2,6,6‐tetramethyl‐1‐piperidine‐N‐oxyl (TEMPO)‐mediated GOR reaction is explored to produce a valorized C3 product, highlighting key selectivity differences between the two methods despite using the same optimized electrolyte composition. Increasing the pH of the solution dramatically increases GOR activity but presents a tradeoff with the stability of TEMPO. At an optimal pH of 10.6 in carbonate buffer in a batch reactor, the reaction proceeds with higher than 90% yield via a 10‐electron oxidation to mesoxalic acid, a C3 product. FE at much lower Reynolds number yields significantly lower selectivity toward C3, demonstrating a high sensitivity to mass transport. The work sheds light on the opportunities toward selectively producing C3 products from GOR as well as the importance of mass transfer considerations for the valorization of this key bio‐feedstock and for others involving mediated electrocatalysis.
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- Award ID(s):
- 2029326
- PAR ID:
- 10649927
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- ChemElectroChem
- ISSN:
- 2196-0216
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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null (Ed.)Organic electrosynthesis is emerging as a cost-effective and environmental-friendly chemical production strategy by utilizing renewable electricity. Paired electrolysis cogenerates valuable chemicals at both electrodes can optimize the energy efficiency and economic feasibility. We report pairing hydrogenation and oxidation of 5-(hydroxymethyl)furfural (HMF) or furfural to desired chemicals at a single electrolysis cell. Electrocatalytic hydrogenation of HMF to 2,5-bis(hydroxymethyl)furan (BHMF) and furfural to furfural alcohol (FA) with high selectivity of >90% can be operated at near-neutral pH on Ag-based and Pb-based catalysts, respectively. In addition, oxidizing HMF to 2,5-furandicarboxylic acid (FDCA) and furfural to furoic acid can both be realized at TEMPO mediated process by using carbon-based catalysts or at Ni-based catalyst in an alkaline medium. Taken together, HMF or furfural can be performed in a single electrolysis cell with a minimized cell voltage only around 1.6 V. Products selectivity and faradaic efficiency are highly related to the reaction conditions, including potential or current density, architectures of the reactor, type of catalysts. By optimizing the single flow reactor, a three-electrode system, two-electrode membrane assembly architecture, and pH-symmetric and pH-asymmetric structure can be designed to reduce the capital expense, minimize required energy, and simplify processing steps. Finally, a complete electrons economy can be achieved by pairing two electrochemical reactions, and the overall charge efficiency can attain over 170% without any crossover issue detected. As a result, the continuous cogeneration of high value-added BHMF or FA and FDCA or furoic acid can be performed in a single electrolyzer.more » « less
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Abstract Pairing the electrocatalytic hydrogenation (ECH) reaction with different anodic reactions holds great promise for producing value‐added chemicals driven by renewable energy sources. Replacing the sluggish water oxidation with a bio‐based upgrading reaction can reduce the overall energy cost and allows for the simultaneous generation of high‐value products at both electrodes. Herein, we developed a membrane‐electrode assembly (MEA)‐based electrolysis system for the conversion of 5‐(hydroxymethyl)furfural (HMF) to bis(hydroxymethyl)furan (BHMF) and 2,5‐furandicarboxylic acid (FDCA). With (2,2,6,6‐tetramethylpiperidin‐1‐yl)oxyl (TEMPO)‐mediated electrochemical oxidation (ECO) of HMF at the anode, the unique zero‐gap configuration enabled a minimal cell voltage of 1.5 V at 10 mA, which was stable during a 24‐hour period of continuous electrolysis, resulting in a combined faradaic efficiency (FE) as high as 139 % to BHMF and FDCA. High FE was also obtained in a pH‐asymmetric mediator‐free configuration, in which the ECO was carried out in 0.1 M KOH with an electrodeposited NiFe oxide catalyst and a bipolar membrane. Taking advantage of the low cell resistance of the MEA‐based system, we also explored ECH of HMF at high current density (280 mA cm−2), in which a FE of 24 % towards BHMF was achieved. The co‐generated H2was supplied into a batch reactor in tandem for the catalytic hydrogenation of furfural or benzaldehyde under ambient conditions, resulting in an additional 7.3 % of indirect FE in a single‐pass operation. The co‐electrolysis of bio‐derived molecules and the tandem electrocatalytic‐catalytic process provide sustainable avenues towards distributed, flexible, and energy‐efficient routes for the synthesis of valuable chemicals.more » « less
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