Electroreforming of Biomass for Value-Added Products

Abstract

Humanity's overreliance on fossil fuels for chemical and energy production has resulted in uncontrollable carbon emissions that have warranted widespread concern regarding global warming. To address this issue, there is a growing body of research on renewable resources such as biomass, of which cellulose is the most abundant type. In particular, the electrochemical reforming of biomass is especially promising, as it allows greater control over valorization processes and requires milder conditions. Driven by renewable electricity, electroreforming of biomass can be green and sustainable. Moreover, green hydrogen generation can be coupled to anodic biomass electroforming, which has attracted ever-increasing attention. The following review is a summary of recent developments related to electroreforming cellulose and its derivatives (glucose, hydroxymethylfurfural, levulinic acid). The electroreforming of biomass can be achieved on the anode of an electrochemical cell through electrooxidation, as well as on the cathode through electroreduction. Recent advances in the anodic electroreforming of cellulose and cellulose-derived glucose and 5-hydrooxylmethoylfurural (5-HMF) are first summarized. Then, the key achievements in the cathodic electroreforming of cellulose and cellulose-derived 5-HMF and levulinic acid are discussed. Afterward, the emerging research focusing on coupling hydrogen evolution with anodic biomass reforming for the cogeneration of green hydrogen fuel and value-added chemicals is reviewed. The final chapter of this paper provides our perspective on the challenges and future research directions of biomass electroreforming.

Keywords: biomass electroreforming; cellulose; electrochemical hydrogenation; electrooxidation; green hydrogen.

Figure 1

Schematic of biomass electroreforming. The most abundant lignocellulosic biomass is taken as an example. Electroreforming of the major component of lignocellulosic biomass, cellulose, or its derivatives, could offer value-added chemicals and green hydrogen fuel. Electroreforming can be powered by electricity from the grid or renewables, which makes it a promising method of renewable energy storage and green chemistry for a sustainable future.

Figure 2

Cellulose, glucose and its derivatives.

Figure 3

(a) Microscopic images before (i) and after (ii) dissolution. (b) X-ray diffraction of cellulose before (i) and after (ii) dissolution. (c) cyclic voltammogram (vs. Ag/AgCl) of cellulose ball milled to average particle size of 100 nm (i), 500 nm (ii) and without cellulose (iii). (d) size distribution after ball milling to 100 nm (i) and 500 nm (ii). (e) FTIR scans of cellulose before dissolution (i), after dissolution (ii) and after oxidation (iii). Reprinted with permission from Ref. [34]. Copyright 2010, Electroanalysis.

Figure 4

Proposed cellulose oxidation mechanism on electrode surface in alkali media in CV cycle. (a) initial state, with cellulose dissolved in alkali solution. (b) in forward scan region: adsorption of OH⁻ ions to surface of electrode, cellulose molecule approaches OH-Au active sites. (c) oxidation of cellulose at electrode. (d) in reverse scan region: desorption of oxidation product and further oxidation of cellulose at revealed electrode surface. (e) desorption of OH⁻ ions from electrode surface. Reprinted with permission from Ref. [35]. Copyright 2014, ChemSusChem.

Figure 5

(a) SEM image of pretreated CA. (b) SEM of 10 nm Au/CA. (c) Magnified SEM of 10 nm Au/CA. (d) XRD results of 10 nm Au/CA and 50 nm Au/CA electrodes. (e) High performance liquid chromatography results of products using 10 nm Au/CA electrodes. Reprinted with permission from Ref. [36]. Copyright 2015, Catalysis.

Figure 6

(a) CVs (vs. SCE) of 0.5 M sulfuric acid (i) and 0.5 M sulfuric acid with 10 g/L cellulose (ii). (b) Decrease in DP over time at 30 mA/cm². (c) Decrease in DP over time without applied current. Reprinted with permission from Ref. [42]. Copyright 2011, Polymer Degradation and Stability.

Figure 7

Proposed cellulose depolymerization mechanism in acidic media. Reprinted with permission from Ref. [42]. Copyright 2011, Polymer Degradation and Stability.

Figure 8

Nano MnO₂/Ti electrocatalysts in flow-through cells for glucaric acid (GA) and gluconic acid (GLA) production from glucose. (a) SEM image of 5% MnO₂/Ti electrode. (b) Schematic diagram of electrocatalytic flow reactor system. (c) Products at different current densities (under 5% MnO₂ loading, glucose concentration of 50.5 mmol/L, pH of 7, 30 °C, 19 min). Reprinted with permission from Ref. [54]. Copyright 2014, Electrochimica Acta.

Figure 9

(a) TEM image of AuNP capped with decanethiolate monolayer shell (for deposition on electrode). (b) Change in current ratios across time with gold nanoparticles in alkali medium (i), bulk gold in alkali medium (ii), gold nanoparticles in neutral medium (iii), and bulk gold in neutral medium (iv). (c) Plots of electrolysis products with 2 nm AuNP in 0.1 M NaOH, 0.01 M glucose, at different potentials (vs. Ag/AgCl); total current efficiency of all products (i), gluconolactone (ii), oxalate (iii), glyconate (iv), formate (v). Reprinted with permission from Ref. [59]. Copyright 2005, Electrochemistry Communications.

Figure 10

Oxidation pathways and products of 5-HMF.

Figure 11

LSV scans of cobalt alloys in half cell in 1 M KOH, (a) without the addition of 5-HMF (OER), and (b) with the addition of 10 mM 5-HMF (5-HMF oxidation to FDCA). Reprinted with permission from Ref. [67]. Copyright 2018, Beilstein Journal of Organic Chemistry.

Figure 12

(a,b) SEM images of nickel foam before CoB deposition. (c,d) SEM of foam after CoB deposition. (e) LSV in flow reactor with and without 5-HMF. (f) Concentration against time for various products. Reprinted with permission from Ref. [67]. Copyright 2018, Beilstein Journal of Organic Chemistry.

Figure 13

Comparison of LSV graphs with different catalysts. (a) LSV scans of 5 mM of 5-HMF and intermediates (solid lines) and without 5-HMF (dashed line) at a pH of 13 using nanocrystalline Cu foam. Reprinted with permission from Ref. [68]. Copyright 2018, ACS Catalysis. (b) LSV of Ni(OH)₂ catalysts without (blue and black lines) and with 5 mM 5-HMF (red line) at a pH of 13. Reprinted with permission from Ref. [69]. Copyright 2019, ACS Catalysis. (c) LSV of NiCo₂O₄ and Co₃O₄ catalysts without (dashed lines) and with (solid lines) 5 mM 5-HMF, at a pH of 13. Reprinted with permission from Ref. [70]. Copyright 2019, Applied Catalysis B: Environmental. (d) LSV of CoO-CoSe₂ electrocatalysts without (black line) and with (red line) 10 mM 5-HMF at a pH of 13. Reprinted with permission from Ref. [72]. Copyright 2020, Green Chemistry. (e) LSV of Ni₃S₂-Nickel foam without (black line) and with (red line) 10 mM 5-HMF at a pH of 13. Reprinted with permission from Ref. [74]. Copyright 2021, Dalton Transactions. (f) LSV of 20 mM 5-HMF and intermediates (colored lines) and without (black line) with MnO_x at a pH of 1. Reprinted with permission from Ref. [75]. Copyright 2018, ChemSusChem.

Figure 14

Proposed glycerol oxidation pathway over CoO_x in mild alkali media. Reprinted with permission from Ref. [84]. Copyright 2021, Applied Catalysis B: Environmental.

Figure 15

(a) HPLC of oligosaccharides after electrolysis. (b) HPLC of products after hydrothermal treatment of cellulose. (c) Proposed mechanism for cellulose oligosaccharide depolymerization with MnO₂ cathode. Reprinted with permission from Ref. [90]. Copyright 2014, Journal of Industrial and Engineering Chemistry.

Figure 16

Hydrogenation pathways of 5-HMF. Reprinted with permission from Ref. [92]. Copyright 2015, ChemSusChem.

Figure 17

(a) Product selectivities at different cathodic potentials (vs. Ag/AgCl). (b) Product selectivities at different 5-HMF concentrations. Reprinted with permission from Ref. [96]. Copyright 2019, Green Chemistry.

Figure 18

(a) H cell diagram. (b) Flow cell diagram. (c) BMHF and 5,5-bis(hydroxymethyl)hydrofuroin (BHH) results from 5-HMF hydrogenation using Ag or OD-Ag, in H cell or flow cell. Reprinted with permission from Ref. [98]. Copyright 2021, Green Chemistry.

Figure 19

Reaction pathways from levulinic acid to octane.

Figure 20

(a) Schematic of flow cell reactor. (b) Comparison of conversion and (c) Faradaic efficiencies of half-cell against flow cell reactor, at −1.3 V, 0.2 M levulinic acid, 0.5 M H₂SO₄, with Pb electrode. Reprinted with permission from Ref. [104]. Copyright 2013, ChemSusChem.

Figure 21

(a) LSV scan in 2-electrode cell without and with 0.5 M glucose in 10 M KOH, iron phosphide anode. (b) Amount of hydrogen theoretically calculated and collected at 1.9 V, 10 M KOH with and without 0.5 M glucose. Reprinted with permission from Ref. [109]. Copyright 2017, Electrochemistry Communications.

Figure 22

(a) TEM of Pd₃Au₇/C, reprinted with permission from Ref. [110]. Copyright 2019, Applied Catalysis B: Environmental. (b) SEM of Co-Ni alloy, reprinted with permission from Ref. [112]. Copyright 2020, Journal of Alloys and Compounds. (c) SEM of Co_0.5 Ni_0.5(OH)_2, reprinted with permission from Ref. [113]. Copyright 2020, Journal of Electroanalytical Chemistry. (d) SEM of Ni-MoS_2, reprinted with permission from Ref. [114]. Copyright 2020, International Journal of Hydrogen Energy.

Figure 23

(a) SEM image of Fe_0.1CoSe₂/CC. (b) LSV for anodic glucose oxidation, 1 M KOH, 0.5 M glucose with different electrodes. (c) LSV for cathodic hydrogen evolution, 0.5 M H₂SO₄. Reprinted with permission from Ref. [115]. Copyright 2020, Applied Catalysts B: Environmental.

Figure 24

(a) SEM image of carbon pellet. (b) Hydrogen production over days, from carbon oxidation contribution (COC) or oxygen evolution, with a carbon electrode. (c) Hydrogen production under similar conditions with a nitrogen-doped carbon electrode. Reprinted with permission from Ref. [116]. Copyright 2020, ChemSusChem.

Figure 25

(a) LSV of two-electrode cell for concurrent 5-HMF oxidation and hydrogen evolution. (b) Amount of hydrogen theoretically calculated and measured at the cathode. Reprinted with permission from Ref. [118]. Copyright 2016, ACS Energy Letters.

Figure 26

(a) LSV for Ni₃N-V₂O_3, Ni₃N, V₂O₃ and Pt/C cathodes. (b) LSV for Ni₃N-V₂O₃ and Ni₃N anodes with and without 10 mM 5-HMF. (c) Concentrations of 5-HMF and products over time, in two-electrode test cell, 1 M KOH, 10 mM 5-HMF, chronopotentiometric test at 10 mA/cm², Ni₃N-V₂O₃ anode and cathode. (d) Theoretical and actual production of hydrogen gas. Reprinted with permission from Ref. [120]. Copyright 2021, Chemical Engineering Journal.