Electrocatalytic valorization of lignocellulose-derived aromatics at industrial-scale current densities

Abstract

Electrocatalytic hydrogenation of lignocellulosic bio-oil to value-added chemicals offers an attractive avenue to use the increasing intermittent renewable electricity and biomass-derived feedstocks. However, to date the partial current densities to target products of these reactions are lower than those needed for industrial-scale productivity, which limits its prospects. Here we report a flow-cell system equipped with a Rh diffusion electrode to hydrogenate lignocellulose-derived aromatic monomers, such as furans and lignin monomers, to value-added chemicals. We achieve high faradaic efficiencies up to 64% at industrial-scale current densities of 300–500 mA cm−2, representing high productivities to target products. A screening of electrocatalysts indicates that only by highly-electrolyte-permeable Rh diffusion electrodes are we able to unite current density with faradaic efficiency. We apply in-situ infrared reflection–absorption spectroscopy to investigate the electrode-potential-dependent reaction pathways and intermediates, confirming a wide potential window for efficient electrocatalytic hydrogenation of lignocellulose-derived aromatics to target products.

Recent Progress in Electrocatalytic Conversion of Lignin: From Monomers, Dimers, to Raw Lignin

“…Different ex situ, in situ, and more importantly operando characterization techniques from different aspects can facilitate the probing of reaction intermediates and identification of the authentic reactive sites, with comprehensive understanding of the reaction mechanism, which would greatly help the rational design of more effici ent catalysts and reaction systems for electricity-driven lignin conversion. 28,30 Second, the majority of systems focus on the conversion of lignin model compounds. The investigation of raw lignin valorization should be strengthened.…”

“…Based on this premise, they successfully designed a flow-cell system to achieve an industrial current density exceeding 400 mA cm −2 using Rh-covered PTFE electrodes, while also obtaining a significant 57.8% FE to methoxylated cyclohexane derivatives. 30 The high permeability of Rh diffusion electrodes to electrolytes was crucial for enhancing the FE and decreasing the flow-cell voltage.…”

“…As a result, studies on the electrocatalytic conversion of lignin typically commence with lignin monomers and dimers. Although several reviews have summarized the advancements in the electrocatalytic reduction of lignin monomers and dimers, as well as the oxidation of lignin dimers through hydrogen atom transfer (HAT) mediators, insufficient notice has been given to the progress in electrocatalytic oxidation strategy, the conversion of raw lignin, and the design of electrocatalysts. − Moreover, exciting achievements regarding catalyst design for electrocatalytic lignin conversion have been witnessed in recent years, which is probably benefited from the progress in catalyst synthesis method, characterization and mechanism understanding in a more precise fashion. − Hence, it is imperative to undertake a review on advanced catalyst design for electrocatalytic conversion of lignin.…”

Protocol for electrocatalytic hydrogenation of 5-hydroxymethylfurfural using H and flow cells

“…Biomass resources serve as one of a few renewable organic carbon in nature but their complete commercial application remains untapped. 2 , 3 , 4 Annually, an excess of 40 million tons of non-consumable plant material is disposed of, leading to a substantial accumulation of biomass waste. 5 However, biomass has been identified as an attractive research direction due to the potential utilization of biomass-derived products in the pharmaceutical industry.…”

Cu–Sn Bimetallic Activated Carbon–Carbon Coupling for Efficient Furfural Electroreduction

“…The selective hydrogenation of biomass-derived platform compounds, such as furfural and 5-hydroxymethylfurfural, is a crucial reaction for producing biomass fuel. − However, the alkane with a short alkyl chain is unsuitable for “drop-in” fuel due to the high volatility and low energy density. , Therefore, furfural and 5-hydroxymethylfurfural need to be updated through C–C coupling reactions to produce high-quality fuel. − Previous studies have indicated that electrocatalytic hydrogenation reaction (ECH) is more likely to occur on catalysts with a lower hydrogen evolution overpotential, such as Pt-group metals, which leads to the formation of furfuryl alcohol and 2-methylfuran as the predominant products. − In contrast, electrocatalytic dimerization reactions (ECD) are more probable to occur on catalysts with higher hydrogen evolution overpotential, such as Pb, Hg, Sn, and graphite. − By performing mechanism analysis, it has been discovered that electroreduction of furfural can yield * fur -CHOH (* denotes the adsorbed species on the surface) radicals through a Langmuir–Hinshelwood process (L–H) resulting in additional C–C coupling reactions and formation of dimers. , Moreover, precisely controlling the *H is required to ensure the accurate formation of * fur -CHOH radicals, which can prevent overhydrogenation into undesired byproducts such as furfuryl alcohol or hydrogen gas production. , Consequently, balancing the * fur -CHOH and * H coverage on the catalyst surface can regulate the reaction adopting an ECH or ECD pathway, which can ultimately promote the selectivity and yield of higher carbon products.…”