High-Grade Biofuel Synthesis from Paired Electrohydrogenation and Electrooxidation of Furfural Using Symmetric Ru/Reduced Graphene Oxide Electrodes

Biomass Valorization via Paired Electrocatalysis

Electrochemical valorization of biomass represents an emerging research frontier, capitalizing on renewable feedstocks to mitigate carbon emissions. Traditional electrochemical approaches often suffer from energy inefficiencies due to the requirement of a second electrochemical conversion at the counter electrode which might generate non-value-added byproducts. This review article presents the advancement of paired electrocatalysis as an alternative strategy, wherein both half-reactions in an electrochemical cell are harnessed to concurrently produce value-added chemicals from biomass-derived feedstocks, potentially doubling the Faradaic efficiency of the whole process. The operational principles and advantages of different cell configurations, including 1-compartment undivided cells, H-type cells, and flow cells, in the context of paired electrolysis are introduced and compared, followed by the analysis of various catalytic strategies, from catalyst-free systems to sophisticated homogeneous and heterogeneous electrocatalysts, tailored for optimized performance. Key substrates, such as CO2, 5-hydroxymethylfurfural (HMF), furfural, glycerol, and lignin are highlighted to demonstrate the versatility and efficacy of paired electrocatalysis. This work aims to provide a clear understanding of why and how both cathode and anode reactions can be effectively utilized in electrocatalytic biomass valorization leading to innovative industrial scalability.

Development status of electrocatalytic hydrogenation of biomass small molecules and prospects for industrial production

Biomass is the only renewable organic carbon resource in nature, and utilization of biomass is important for carbon neutrality. Currently, depolymerizing biomass macromolecules into small organic monomers via thermocatalytic pyrolysis is a well-established technique. Further valorization of these biomass small molecules to value-added products has attracted increasing attention, especially via electrochemistry coupling green electricity. Electrocatalytic hydrogenation (ECH) directly uses hydrogen from water and operates under mild conditions (e.g., ambient temperature and pressure), which plays an important role for upgrading biomass small molecules and avoids substantial CO2 emission. In this review, we will provide a summary of recent achievements in ECH of biomass small molecules, with a review focus on the research about pushing ECH toward industrial-scale productivities. We will also discuss the existing problems and challenges in this field and propose an outlook for the future developments.

Rational Design of Transition-Metal-Based Catalysts for the Electrochemical 5-Hydroxymethylfurfural Reduction Reaction

The electrochemical reduction reaction (HMFRR) of 5-hydroxymethylfurfural (HMF) has emerged as a promising avenue for the utilization and refinement of the biomass-derived platform molecule HMF into high-value chemicals, addressing energy sustainability challenges. Transition metal electrocatalysts (TMCs) have recently garnered attention as promising candidates for catalyzing HMFRR, capitalizing on the presence of vacant d orbitals and unpaired d electrons. TMCs play a pivotal role in facilitating the generation of intermediates through interactions with HMF, thereby lowering the activation energy of intricate reactions and significantly augmenting the catalytic reaction rate. In the absence of comprehensive and guiding reviews in this domain, this paper aims to comprehensively summarize the key advancements in the design of transition metal catalysts for HMFRR. It elucidates the mechanisms and pH dependency of various products generated during the electrochemical reduction of HMF, with a specific emphasis on the bond-cleavage angle. Additionally, it offers a detailed introduction to typical in-situ characterization techniques. Finally, the review explores engineering strategies and principles to enhance HMFRR activity using TMCs, particularly focusing on multiphase interface control, crystal face control, and defect engineering control. This review introduces novel concepts to guide the design of HMFRR electrocatalysts, especially TMCs, thus promoting advancements in biomass conversion.

Efficient Electrochemical Hydrogenation of Furfural to Furfuryl Alcohol Using an Anion-Exchange Membrane Electrolysis Cell

The electrochemical hydrogenation (ECH) of furfural (FF) offers a promising pathway for the production of furfuryl alcohol (FA) while aligning with sustainability and environmental considerations. However, this technology has primarily been studied in half-cell configurations operating at high cell voltages and low current densities. Herein, we employ a membrane electrode assembly (MEA) system with an anion-exchange membrane for the ECH of FF and systematically investigate various parameters, including the ionomer content in the cathode catalyst, electrolyte type, electrolyte concentration, and flow rate. Under optimal conditions, our MEA system with non-noble metal-based catalysts exhibits a current density of 30 mA cm-2 with a Faradaic efficiency for FA production of 66% at a cell voltage of 2 V, maintaining operational durability for 5 h. This study highlights the potential of electrochemical FA production for practical applications to realize the decarbonization of the hydrogenation industry.

Nanostructured electrocatalysts for organic synthetic transformations

Organic chemists have made and are still making enormous efforts toward the development of novel green catalytic synthesis. The necessity arises from the imperative of safeguarding human health and the environment, while ensuring efficient and sustainable chemical production. Within this context, electrocatalysis provides a framework for the design of new organic reactions under mild conditions. Undoubtedly, nanostructured materials are under the spotlight as the most popular and in most cases efficient platforms for advanced organic electrosynthesis. This Minireview focuses on the recent developments in the use of nanostructured electrocatalysts, highlighting the correlation between their chemical structures and resulting catalytic abilities, and pointing to future perspectives for their application in cutting-edge areas.

Developing electrochemical hydrogenation towards industrial application

Electrochemical hydrogenation reactions gained significant attention as a sustainable and efficient alternative to conventional thermocatalytic hydrogenations. This tutorial review provides a comprehensive overview of the basic principles, the practical application, and recent advances of electrochemical hydrogenation reactions, with a particular emphasis on the translation of these reactions from lab-scale to industrial applications. Giving an overview on the vast amount of conceivable organic substrates and tested catalysts, we highlight the challenges associated with upscaling electrochemical hydrogenations, such as mass transfer limitations and reactor design. Strategies and techniques for addressing these challenges are discussed, including the development of novel catalysts and the implementation of scalable and innovative cell concepts. We furthermore present an outlook on current challenges, future prospects, and research directions for achieving widespread industrial implementation of electrochemical hydrogenation reactions. This work aims to provide beginners as well as experienced electrochemists with a starting point into the potential future transformation of electrochemical hydrogenations from a laboratory curiosity to a viable technology for sustainable chemical synthesis on an industrial scale.

Ni(1−x)Pdx Alloyed Nanostructures for Electrocatalytic Conversion of Furfural into Fuels

A continuous electrocatalytic reactor offers a promising method for producing fuels and value-added chemicals via electrocatalytic hydrogenation of biomass-derived compounds. However, such processes require a better understanding of the impact of different types of active electrodes and reaction conditions on electrocatalytic biomass conversion and product selectivity. In this work, Ni1−xPdx (x = 0.25, 0.20, and 0.15) alloyed nanostructures were synthesized as heterogeneous catalysts for the electrocatalytic conversion of furfural. Various analytical tools, including XRD, SEM, EDS, and TEM, were used to characterize the Ni1−xPdx catalysts. The alloyed catalysts, with varying Ni to Pd ratios, showed a superior electrocatalytic activity of over 65% for furfural conversion after 4.5 h of reaction. In addition, various experimental parameters on the furfural conversion reactions, including electrolyte pH, furfural (FF) concentration, reaction time, and applied potential, were investigated to tune the hydrogenated products. The results indicated that the production of 2-methylfuran as a primary product (S = 29.78% after 1 h), using Ni0.85Pd0.15 electrocatalyst, was attributed to the incorporation of palladium and thus the promotion of water-assisted proton transfer processes. Results obtained from this study provide evidence that alloying a common catalyst, such as Ni with small amounts of Pd metal, can significantly enhance its electrocatalytic activity and selectivity.

Insights into the activity of nickel boride/nickel heterostructures for efficient methanol electrooxidation

Designing efficient catalysts and understanding the underlying mechanisms for anodic nucleophile electrooxidation are central to the advancement of electrochemically-driven technologies. Here, a heterostructure of nickel boride/nickel catalyst is developed to enable methanol electrooxidation into formate with a Faradaic efficiency of nearly 100%. Operando electrochemical impedance spectroscopy and in situ Raman spectroscopy are applied to understand the influence of methanol concentration in the methanol oxidation reaction. High concentrations of methanol inhibit the phase transition of the electrocatalyst to high-valent electro-oxidation products, and electrophilic oxygen species (O* or OH*) formed on the electrocatalyst are considered to be the catalytically active species. Additional mechanistic investigation with density functional theory calculations reveals that the potential-determining step, the formation of *CH₂O, occurs most favorably on the nickel boride/nickel heterostructure rather than on nickel boride and nickel. These results are highly instructive for the study of other nucleophile-based approaches to electrooxidation reactions and organic electrosynthesis.

Understanding the role of active sites in electrooxidation reactions is important yet challenging. Here, the authors use operando spectroscopies to monitor the effect of methanol concentration on Ni₃B/Ni heterostructures during formate production.

Transform electrocatalytic biomass upgrading and hydrogen production from electricity input to electricity output

Integrating biomass upgrading and hydrogen production in an electrocatalytic system is attractive both environmentally and sustainably. Conventional electrolyzer systems coupling anodic bio-substrate electrooxidation with hydrogen evolution reaction usually require electricity input. In this work, we develop a fuel cell electrocatalytic system achieve the biomass upgrading and hydrogen production as well as electricity generation. Different with conventional furfural electrooxidation, the employed low-potential furfural oxidation enables the hydrogen atom of the aldehyde group to be released as gaseous hydrogen at the anode under a low potential of ~0 VRHE (vs. reversible hydrogen electrode). The integrated fuel cell system could generate electricity of ~2 kWh for per cubic meter of hydrogen produced. This work may provide a transformative technology that turns the electrocatalytic biomass upgrading and hydrogen production from electricity input to electricity output.