Electrocatalytic functional group conversion-based carbon resource upgrading

The conversions of carbon resources, such as alcohols, aldehydes/ketones, and ethers, have been being one of the hottest topics most recently for the goal of carbon neutralization. The emerging electrocatalytic upgrading has been regarded as a promising strategy aiming to convert carbon resources into value-added chemicals. Although exciting progress has been made and reviewed recently in this area by mostly focusing on the explorations of valuable anodic oxidation or cathodic reduction reactions individually, however, the reaction rules of these reactions are still missing, and how to purposely find or rationally design novel but efficient reactions in batches is still challenging. The properties and transformations of key functional groups in substrate molecules play critically important roles in carbon resources conversion reactions, which have been paid more attention to and may offer hidden keys to achieve the above goal. In this review, the properties of functional groups are addressed and discussed in detail, and the reported electrocatalytic upgrading reactions are summarized in four categories based on the types of functional groups of carbon resources. Possible reaction pathways closely related to functional groups will be summarized from the aspects of activation, cleavage and formation of chemical bonds. The current challenges and future opportunities of electrocatalytic upgrading of carbon resources are discussed at the end of this review.

Biomass-Derived Catalytically Active Carbon Materials for the Air Electrode of Zn-air Batteries

Given the growing environmental and energy problems, developing clean, renewable electrochemical energy storage devices is of great interest. Zn-air batteries (ZABs) have broad prospects in energy storage because of their high specific capacity and environmental friendliness. The unavailability of cheap air electrode materials and effective and stable oxygen electrocatalysts to catalyze air electrodes are main barriers to large-scale implementation of ZABs. Due to the abundant biomass resources, self-doped heteroatoms, and unique pore structure, biomass-derived catalytically active carbon materials (CACs) have great potential to prepare carbon-based catalysts and porous electrodes with excellent performance for ZABs. This paper reviews the research progress of biomass-derived CACs applied to ZABs air electrodes. Specifically, the principle of ZABs and the source and preparation method of biomass-derived CACs are introduced. To prepare efficient biomass-based oxygen electrocatalysts, heteroatom doping and metal modification were introduced to improve the efficiency and stability of carbon materials. Finally, the effects of electron transfer number and H2 O2 yield in ORR on the performance of ZABs were evaluated. This review aims to deepen the understanding of the advantages and challenges of biomass-derived CACs in the air electrodes of ZABs, promote more comprehensive research on biomass resources, and accelerate the commercial application of ZABs.

Amorphous Ni-Mo-B-O Bifunctional Electrocatalyst for Simultaneous Production of Hydrogen and Value-added Chemicals

Hydrogen evolution reaction (HER) coupled with biomass conversion is a sustainable route to produce clean energy H2 and value-added chemicals simultaneously. Herein, an amorphous Ni-Mo-B-O bifunctional electrocatalyst was synthesized through a facile electrodeposition method and employed as a cathode for HER to produce H2 and as an anode for the conversion of hydroxymethylfurfural (HMF) to furandicarboxylic acid (FDCA). Besides leading to the formation of amorphous structures, the introduction of Mo and B can increase the electron density and optimize the electronic structure of the electrocatalyst, thus substantially increasing the catalytic activity of the catalyst. After continuous reaction at a constant potential of 0.58 V vs. Hg/HgO for 8 hours, the conversion of HMF reached 98.86 %, and the selectivity of the target product FDCA was as high as 92.97 %. Finally, a two-electrolyzer system was constructed using the amorphous Ni-Mo-B-O as both cathode and anode to achieve simultaneous H2 production in the cathode chamber and FDCA production in the anode chamber at a low voltage. This work presents a promising strategy for the design and synthesis of high-performance non-noble metal electrocatalysts for efficient and cost-effective H2 production.

Recent Advances on Transition-Metal-Based Layered Double Hydroxides Nanosheets for Electrocatalytic Energy Conversion

Transition-metal-based layered double hydroxides (TM-LDHs) nanosheets are promising electrocatalysts in the renewable electrochemical energy conversion system, which are regarded as alternatives to noble metal-based materials. In this review, recent advances on effective and facile strategies to rationally design TM-LDHs nanosheets as electrocatalysts, such as increasing the number of active sties, improving the utilization of active sites (atomic-scale catalysts), modulating the electron configurations, and controlling the lattice facets, are summarized and compared. Then, the utilization of these fabricated TM-LDHs nanosheets for oxygen evolution reaction, hydrogen evolution reaction, urea oxidation reaction, nitrogen reduction reaction, small molecule oxidations, and biomass derivatives upgrading is articulated through systematically discussing the corresponding fundamental design principles and reaction mechanism. Finally, the existing challenges in increasing the density of catalytically active sites and future prospects of TM-LDHs nanosheets-based electrocatalysts in each application are also commented.

Unravelling and overcoming the challenges in the electrocatalytic reduction of fructose to sorbitol

In this work, we present a comprehensive study of the electrocatalytic reduction of fructose to sorbitol and mannitol, in a mild alkaline medium (pH = 11.3), with a Cu wire as the cathode. Particular attention was paid to the reaction mechanism, investigated by linear sweep voltammetry (LSV) and chronopotentiometry (CP) coupled with high-pressure liquid chromatography (HPLC). The initial results of our study showed that at the potential where the fructose reduction reaction (FRR) is achieved, competition with the hydrogen evolution reaction (HER) tends to occur, thus limiting the Faradaic efficiency towards the FRR. Moreover, products of chemical conversions were also observed in the liquid electrolyte, originating from the isomerisation of fructose to glucose and mannose and degradation reactions (C-C breaking). Through a thorough optimisation of the reaction parameters, the Faradaic efficiency could be remarkably improved, reaching values >40% and being sustained for 10 h of electrolysis at a current of i = -20 mA. More specifically, the minimisation of the undesired chemical side reactions was achieved by the careful control of the pH (11.3 ± 0.3) using a buffer electrolyte and a titration pump, thus limiting the isomerisation of fructose to glucose and mannose to <2% in 10 h. The electrochemical conversion was optimised via a tailored strategy involving a two-step potential cycling for re-activating the electrocatalyst surface, which allowed achieving 77% electrochemical conversion of fructose to sorbitol and mannitol in 10 h of electrolysis (sorbitol : mannitol = 0.43 : 0.57). This is the first time that the electrocatalytic FRR was achieved with such a high product yield and by using a non-noble metal-based cathode, thus opening up a novel, green route for the conversion of fructose into sorbitol and mannitol. This work also provides relevant, new insight into the crucial parameters that need to be taken into account to achieve the electrocatalytic reduction of saccharides, by gaining control of their complex chemistry in solution.

Hydrogenation of Carboxylic Acids, Esters, and Related Compounds over Heterogeneous Catalysts: A Step toward Sustainable and Carbon-Neutral Processes

The catalytic hydrogenation of esters and carboxylic acids represents a fundamental and important class of organic transformations, which is widely applied in energy, environmental, agricultural, and pharmaceutical industries. Due to the low reactivity of the carbonyl group in carboxylic acids and esters, this type of reaction is, however, rather challenging. Hence, specifically active catalysts are required to achieve a satisfactory yield. Nevertheless, in recent years, remarkable progress has been made on the development of catalysts for this type of reaction, especially heterogeneous catalysts, which are generally dominating in industry. Here in this review, we discuss the recent breakthroughs as well as milestone achievements for the hydrogenation of industrially important carboxylic acids and esters utilizing heterogeneous catalysts. In addition, related catalytic hydrogenations that are considered of importance for the development of cleaner energy technologies and a circular chemical industry will be discussed in detail. Special attention is paid to the insights into the structure-activity relationship, which will help the readers to develop rational design strategies for the synthesis of more efficient heterogeneous catalysts.

Preliminary Studies on the Electrochemical Conversion of Liquefied Forest Biomass

Bio-oils produced from three different biomass sources, namely cork, pinewood, and olive stones, are evaluated concerning their suitability and prospects of including their electrochemical transformations in a biorefinery scenario for the production of added-value compounds. Different types and concentrations of electrolytes (e.g., H2SO4, KOH) are added to the bio-oils to increase the samples’ initially low ionic conductivity. The samples prepared by mixing bio-oil with 2 M KOH aqueous solution (50 vol.%) lead to a stable and homogeneous bio-oil alkaline emulsion suitable for electrochemical studies. The bio-oil samples are characterized by physicochemical methods (e.g., density, viscosity, conductivity), followed by analyzing their electrochemical behavior by voltammetric and chronoamperometric studies. The organics electrooxidation and the hydrogen evolution reaction in the bio-oils are assessed using Pt electrodes. Single- and two-compartment cell laboratory bio-oil electrolyzers are assembled using nickel plate electrodes. Electrolysis is carried out at 2.5 V for 24 h. Attenuated Total Reflection-Fourier-Transform Infrared Spectroscopy and Mass Spectrometry are applied to identify possible changes in the bio-oil samples’ chemical structure during the electrolysis experiments. Comparing the analyses of the bio-oil samples subjected to electrolysis with the blank samples demonstrates that bulk electrolysis significantly changes the bio-oil composition. The bio-oil obtained from cork biomass shows the most promising results, but further studies are required to understand the nature of the actual changes.

Hybrid bilayer membranes as platforms for biomimicry and catalysis

Hybrid bilayer membrane (HBM) platforms represent an emerging nanoscale bio-inspired interface that has broad implications in energy catalysis and smart molecular devices. An HBM contains multiple modular components that include an underlying inorganic surface with a biological layer appended on top. The inorganic interface serves as a support with robust mechanical properties that can also be decorated with functional moieties, sensing units and catalytic active sites. The biological layer contains lipids and membrane-bound entities that facilitate or alter the activity and selectivity of the embedded functional motifs. With their structural complexity and functional flexibility, HBMs have been demonstrated to enhance catalytic turnover frequency and regulate product selectivity of the O₂ and CO₂ reduction reactions, which have applications in fuel cells and electrolysers. HBMs can also steer the mechanistic pathways of proton-coupled electron transfer (PCET) reactions of quinones and metal complexes by tuning electron and proton delivery rates. Beyond energy catalysis, HBMs have been equipped with enzyme mimics and membrane-bound redox agents to recapitulate natural energy transport chains. With channels and carriers incorporated, HBM sensors can quantify transmembrane events. This Review serves to summarize the major accomplishments achieved using HBMs in the past decade.

Conductive Metal-Organic Frameworks Bearing M-O4 Active Sites as Highly Active Biomass Valorization Electrocatalysts

The electrochemical oxidation of the biomass platform 5-hydroxymethylfurfural (HMF) to 2,5-furandicarboxylic acid (FDCA), is an important reaction in the emerging area of renewable energy-powered biomass valorization. A key limitation in this field is the ill-defined nature of the catalytic sites of the highest-performing materials that limits the fundamental insights that can be extracted. To this end, a conductive metal-organic framework-based electrocatalytic model system with well-defined M-O₄ active sites for electrochemical HMF oxidation was developed. These materials were found to be highly active towards FDCA generation, with product yields of over 95 %. In parallel, infrared spectroscopy was employed to capture a surface-bound aldehyde group as the key intermediate in the catalytic cycle, which forms once M(II/III) oxidation occurs. This work illustrates the advantage of utilizing molecularly defined active sites coupled with operando spectroscopy to provide fundamental insights into a variety of electrosynthetic reactions and thus paves the way for future catalyst design.

Metal vs. Metal-Free Catalysts for Oxidation of 5-Hydroxymethylfurfural and Levoglucosenone to Biosourced Chemicals

Lignocellulosic feedstocks, such as forestry biomass and agricultural crop residues, can be utilized to generate biofuels and biochemicals. Converting these organic waste materials into biochemicals is widely regarded as a remedial approach to develop a sustainable, clean, and green energy source. Nevertheless, are these methods sustainable and clean? Prior studies have shown that most such conversions use metals - including heavy metals or noble metals - as catalysts. In addition to the fact that many metals (e. g., aluminum, cobalt, titanium, platinum) have been listed as critical minerals, these methods suffer from high cost, deactivation, and leakage problems and the release of toxic wastes. This Review summarizes catalytic methods using metal and metal-free catalysts for the oxidation of the platform molecules 5-hydroxymethylfurfural and levoglucosenone and demonstrates the potential and effectiveness of metal-free catalysts.

Selective Electrooxidation of Biomass-Derived Alcohols to Aldehydes in a Neutral Medium: Promoted Water Dissociation over a Nickel-Oxide-Supported Ruthenium Single-Atom Catalyst

The biomass-derived alcohol oxidation reaction (BDAOR) holds great promise for sustainable production of chemicals. However, selective electrooxidation of alcohols to value-added aldehyde compounds is still challenging. Herein, we report the electrocatalytic BDAORs to selectively produce aldehydes using single-atom ruthenium on nickel oxide (Ru₁ -NiO) as a catalyst in the neutral medium. For electrooxidation of 5-hydroxymethylfurfural (HMF), Ru₁ -NiO exhibits a low potential of 1.283 V at 10 mA cm^-2 , and an optimal 2,5-diformylfuran (DFF) selectivity of 90 %. Experimental studies reveal that the neutral electrolyte plays a critical role in achieving a high aldehyde selectivity, and the single-atom Ru boosts HMF oxidation in the neutral medium by promoting water dissociation to afford OH*. Furthermore, Ru₁ -NiO can be extended to selective electrooxidation of a series of biomass-derived alcohols to corresponding aldehydes, which are conventionally difficult to obtain in the alkaline medium.

Catalysis for e-Chemistry: Need and Gaps for a Future De-Fossilized Chemical Production, with Focus on the Role of Complex (Direct) Syntheses by Electrocatalysis

The prospects, needs and limits in current approaches in catalysis to accelerate the transition to e-chemistry, where this term indicates a fossil fuel-free chemical production, are discussed. It is suggested that e-chemistry is a necessary element of the transformation to meet the targets of net zero emissions by year 2050 and that this conversion from the current petrochemistry is feasible. However, the acceleration of the development of catalytic technologies based on the use of renewable energy sources (indicated as reactive catalysis) is necessary, evidencing that these are part of a system of changes and thus should be assessed from this perspective. However, it is perceived that the current studies in the area are not properly addressing the needs to develop the catalytic technologies required for e-chemistry, presenting a series of relevant aspects and directions in which research should be focused to develop the framework system transformation necessary to implement e-chemistry.

CoP nanorods anchored on Ni2P-NiCoP nanosheets with abundant heterogeneous interfaces boosting the electrocatalytic oxidation of 5-hydroxymethyl-furfural

CoP nanorods anchored on Ni2P-NiCoP nanosheets have been fabricated. The heterogeneous interfaces can regulate the d-band centers of Co and Ni to approach the Fermi level, thus boosting the electrocatalytic oxidation of HMF.

Electroreforming of Biomass for Value-Added Products

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.

Understanding the Roles of Electrogenerated Co3+ and Co4+ in Selectivity-Tuned 5-Hydroxymethylfurfural Oxidation

The Co-based electrocatalyst is among the most promising candidates for electrochemical oxidation of 5-hydroxymethylfurfural (HMF). However, the intrinsic active sites and detailed mechanism of this catalyst remains unclear. We combine experimental evidence and a theoretical study to show that electrogenerated Co³⁺ and Co⁴⁺ species act as chemical oxidants but with distinct roles in selective HMF oxidation. It is found that Co³⁺ is only capable of oxidizing formyl group to produce carboxylate while Co⁴⁺ is required for the initial oxidation of hydroxyl group with significantly faster kinetics. As a result, the product distribution shows explicit dependence on the Co oxidation states and selective production of 5-hydroxymethyl-2-furancarboxylic acid (HMFCA) and 2,5-furandicarboxylic acid (FDCA) are achieved by tuning the applied potential. This work offers essential mechanistic insight on Co-catalyzed organic oxidation reactions and might guide the design of more efficient electrocatalysts.

Probing electrosynthetic reactions with furfural on copper surfaces

This work entails the integrated use of electrochemistry and operando Raman spectroscopy to probe the reduction of a biomass platform, furfural, to value-added chemicals on Cu electrodes. The results reveal key structural differences of the Cu that dictate selectivity for furfuryl alcohol or 2-methylfuran.

Rational incorporation of defects within metal-organic frameworks generates highly active electrocatalytic sites

The allure of metal–organic frameworks (MOFs) in heterogeneous electrocatalysis is that catalytically active sites may be designed a priori with an unparalleled degree of control. An emerging strategy to generate coordinatively-unsaturated active sites is through the use of organic linkers that lack a functional group that would usually bind with the metal nodes. To execute this strategy, we synthesize a model MOF, Ni-MOF-74 and incorporate a fraction of 2-hydroxyterephthalic acid in place of 2,5-dihydroxyterephthalic acid. The defective MOF, Ni-MOF-74D, is evaluated vs. the nominally defect-free Ni-MOF-74 with a host of ex situ and in situ spectroscopic and electroanalytical techniques, using the oxidation of hydroxymethylfurtural (HMF) as a model reaction. The data indicates that Ni-MOF-74D features a set of 4-coordinate Ni–O₄ sites that exhibit unique vibrational signatures, redox potentials, binding motifs to HMF, and consequently superior electrocatalytic activity relative to the original Ni-MOF-74 MOF, being able to convert HMF to the desired 2,5-furandicarboxylic acid at 95% yield and 80% faradaic efficiency. Furthermore, having such rationally well-defined catalytic sites coupled with in situ Raman and infrared spectroelectrochemical measurements enabled the deduction of the reaction mechanism in which co-adsorbed *OH functions as a proton acceptor in the alcohol oxidation step and carries implications for catalyst design for heterogeneous electrosynthetic reactions en route to the electrification of the chemical industry.

The allure of metal–organic frameworks (MOFs) in heterogeneous electrocatalysis is that catalytically active sites may be designed a priori with an unparalleled degree of control.

Advances in Electrochemical Modification Strategies of 5-Hydroxymethylfurfural

The development of electrochemical catalytic conversion of 5-hydroxymethylfurfural (HMF) has recently gained attention as a potentially scalable approach for both oxidation and reduction processes yielding value-added products. While the possibility of electrocatalytic HMF transformations has been demonstrated, this growing research area is in its initial stages. Additionally, its practical applications remain limited due to low catalytic activity and product selectivity. Understanding the catalytic processes and design of electrocatalysts are important in achieving a selective and complete conversion into the desired highly valuable products. In this Minireview, an overview of the most recent status, advances, and challenges of oxidation and reduction processes of HMF was provided. Discussion and summary of voltammetric studies and important reaction factors (e. g., catalyst type, electrode material) were included. Finally, biocatalysts (e. g., enzymes, whole cells) were introduced for HMF modification, and future opportunities to combine biocatalysts with electrochemical methods for the production of high-value chemicals from HMF were discussed.

An Overview of Glycerol Electrooxidation Mechanisms on Pt, Pd and Au

In the most recent decade, glycerol electrooxidation (GEOR) has attracted extensive research interest for valorization of glycerol: the conversion of glycerol to value-added products. These reactions at platinum, palladium, and gold electrodes have a lot of uncertainty in their reaction mechanisms, which has generated some controversies. This review gathers many reported experimental results, observations and proposed reaction mechanisms in order to draw a full picture of GEOR. A particular focus is the clarification of two propositions: Pd is inferior to Pt in cleaving the C-C bonds of glycerol during the electrooxidation and the massive production of CO₂ at high overpotentials is due to the oxidation of the already-oxidized carboxylate products. It is concluded that the inferior C-C bond cleavability with Pd electrodes, as compared with Pt electrodes, is due to the inefficiency of deprotonation, and the massive generation of CO₂ as well as other C1/C2 side products is partially caused by the consumption of OH^- at the anodes, as a lower pH reduces the amount of carboxylates and favors the C-C bond scission. A reaction mechanism is proposed in this review, in which the generation of side products are directly from glycerol ("competition" between each side product) rather than from the further oxidation of C2/C3 products. Additionally, GEOR results and associated interpretations for Ni electrodes are presented, as well as a brief review on the performances of multi-metallic electrocatalysts (most of which are nanocatalysts) as an introduction to these future research hotpots.

Electrocatalysis for Chemical and Fuel Production: Investigating Climate Change Mitigation Potential and Economic Feasibility

The manufacture of goods from oil, coal, or gas to everyday consumer products comprises in more or less all cases at least one catalytic step. Compared to conventional hydrothermal catalysis, electrocatalysis possesses the advantage of mild operational conditions and high selectivity, yet the potential energy savings and climate change mitigation have rarely been assessed. This study conducted a life cycle assessment (LCA) for the electrocatalytic oxidation of crude glycerol to produce lactic acid, one of the most common platform chemicals. The LCA results demonstrated a 31% reduction in global warming potential (GWP) compared to the benchmark (bio- and chemocatalytic) processes. Additionally, electrocatalysis yielded a synergetic potential to mitigate climate change depending on the scenario. For example, electrocatalysis combined with a low-carbon-intensity grid can reduce GWP by 57% if the process yields lactic acid and lignocellulosic biofuel as compared to a conventional fossil-based system with functionally equivalent products. This illustrates the potential of electrocatalysis as an important contributor to climate change mitigation across multiple industries. A technoeconomic analysis (TEA) for electrocatalytic lactic acid production indicated considerable challenges in economic feasibility due to the significant upfront capital cost. This challenge could be largely addressed by enabling dual redox processing to produce separate streams of renewable chemicals and biofuels simultaneously.

Recent catalytic routes for the preparation and the upgrading of biomass derived furfural and 5-hydroxymethylfurfural

Furans represent one of the most important classes of intermediates in the conversion of non-edible lignocellulosic biomass into bio-based chemicals and fuels. At present, bio-furan derivatives are generally obtained from cellulose and hemicellulose fractions of biomass via the acid-catalyzed dehydration of their relative C6-C5 sugars and then converted into a wide range of products. Furfural (FUR) and 5-hydroxymethylfurfural (HMF) are surely the most used furan-based feedstocks since their chemical structure allows the preparation of various high-value-added chemicals. Among several well-established catalytic approaches, hydrogenation and oxygenation processes have been efficiently adopted for upgrading furans; however, harsh reaction conditions are generally required. In this review, we aim to discuss the conversion of biomass derived FUR and HMF through unconventional (transfer hydrogenation, photocatalytic and electrocatalytic) catalytic processes promoted by heterogeneous catalytic systems. The reaction conditions adopted, the chemical nature and the physico-chemical properties of the most employed heterogeneous systems in enhancing the catalytic activity and in driving the selectivity to desired products are presented and compared. At the same time, the latest results in the production of FUR and HMF through novel environmental friendly processes starting from lignocellulose as well as from wastes and by-products obtained in the processing of biomass are also overviewed.

Nickel Iron Diselenide for Highly Efficient and Selective Electrocatalytic Conversion of Methanol to Formate

The electro-oxidation of methanol to formate is an interesting example of the potential use of renewable energies to add value to a biosourced chemical commodity. Additionally, methanol electro-oxidation can replace the sluggish oxygen evolution reaction when coupled to hydrogen evolution or to the electroreduction of other biomass-derived intermediates. But the cost-effective realization of these reaction schemes requires the development of efficient and low-cost electrocatalysts. Here, a noble metal-free catalyst, Ni_{1- x} Fe_x Se₂ nanorods, with a high potential for an efficient and selective methanol conversion to formate is demonstrated. At its optimum composition, Ni_0.75 Fe_0.25 Se₂ , this diselenide is able to produce 0.47 mmol cm^-2  h^-1 of formate at 50 mA cm^-2 with a Faradaic conversion efficiency of 99%. Additionally, this noble-metal-free catalyst is able to continuously work for over 50 000 s with a minimal loss of efficiency, delivering initial current densities above 50 mA cm^-2 and 2.2 A mg^-1 in a 1.0 m KOH electrolyte with 1.0 m methanol at 1.5 V versus reversible hydrogen electrode. This work demonstrates the highly efficient and selective methanol-to-formate conversion on Ni-based noble-metal-free catalysts, and more importantly it shows a very promising example to exploit the electrocatalytic conversion of biomass-derived chemicals.

Operando spectroscopy of nanoscopic metal/covalent organic framework electrocatalysts

Metal and covalent organic frameworks (MOFs and COFs) are increasingly finding exceptional utility in electrocatalytic systems. Their chemically defined porous nature grants them key functions that may enhance their electrocatalytic performance relative to conventional molecular or heterogeneous materials. In order to obtain insights into their function, mechanism, and dynamics under electrocatalytic conditions, operando spectroscopy, that which is performed as the catalyst is functioning, has been increasingly applied. This mini review highlights several key works emerging in recent years that have used various operando spectroscopic techniques, namely UV-vis absorption, Raman, Infrared, and X-ray absorption spectroscopy, to investigate electrocatalytic MOFs and COFs. A brief introduction to each technique and how it was applied to investigate MOF/COF-based electrolytic systems is detailed. The unique set of data obtained, interpretations made, and progress attained all point to the power of operando spectroscopy in truly opening the functionality of MOFs and COFs across many aspects of catalysis.

Hydrogen and Potassium Acetate Co-Production from Electrochemical Reforming of Ethanol at Ultrathin Cobalt Sulfide Nanosheets on Nickel Foam

The sluggish reaction kinetics of the anodic oxygen evolution reaction increases the energy consumption of the overall water electrolysis for high-purity hydrogen generation. In this work, ultrathin cobalt sulfide nanosheets (Co₃S₄-NSs) on nickel foam (Ni-F) nanohybrids (termed as Co₃S₄-NSs/Ni-F) are synthesized using cyanogel hydrolysis and a sulfurization two-step approach. Physical characterizations reveal that Co₃S₄-NSs with a 1.7 nm thickness have abundant holes, implying the big surface area, abundant active edge atoms, and sufficient active sites. Electrochemical measurements show that as-synthesized Co₃S₄-NSs/Ni-F have excellent electrocatalytic activity and selectivity for ethanol oxidation reaction and hydrogen evolution reaction. Due to their bifunctional property of Co₃S₄-NSs/Ni-F nanohybrids, a symmetric Co₃S₄-NSs/Ni-F∥Co₃S₄-NSs/Ni-F ethanol electrolyzer can be effectively constructed, which only requires a 1.48 V electrolysis voltage to reach a current density of 10 mA cm^-2 for high-purity hydrogen generation at the cathode as well as value-added potassium acetate generation at the anode, much lower than the electrolysis voltage of traditional electrochemical water splitting (1.64 V).

A Divergent Paired Electrochemical Process for the Conversion of Furfural Using a Divided-Cell Flow Microreactor

Furfural is a prominent, non-petroleum-based chemical feedstock material, derived from abundantly available hemicellulose. Hence, its derivatization into other useful biobased chemicals is a subject of high interest in contemporary academic and industrial research activities. While most strategies to convert furfural require energy-intensive reaction routes, the use of electrochemical activation allows to provide a sustainable and green alternative. Herein, a disparate approach for the conversion of furfural is reported based on a divergent paired electrochemical conversion, enabling the simultaneous production of 2(5H)-furanone via an anodic oxidation, and the generation of furfuryl alcohol and/or hydrofuroin via a cathodic reduction. Using water as solvent and NaBr as supporting electrolyte and electron-mediator, a green and sustainable process was developed, which maximizes productive use of electricity and minimizes byproduct formation.

Innovative Protocols in the Catalytic Oxidation of 5-Hydroxymethylfurfural

5-Hydroxymethylfurfural (HMF) has been identified as one of the most promising biomass-based multi-purpose platform molecules. Innovative protocols, namely electrocatalysis, photocatalysis, and microwave (MW)-assisted chemistry, as well as continuous-flow systems, add a new dimension and another promising toolbox for the oxidation of HMF in recent years. This Minireview deals with recent progress in the catalytic oxidation of HMF to 2,5-furandicarboxylic acid (FDCA) and other intermediates using noble, non-noble, and metal-free systems deploying emerging protocols. Selective HMF downstream oxidation products could be obtained not only via common catalyst modifications, namely nature of the metal, preparative method, and the property of deployed support, but also by using innovative processes.

Nitrogen modulated NiMoO4 with enhanced activity for the electrochemical oxidation of 5-hydroxymethylfurfural to 2,5-furandicarboxylic acid

NiMoO4 catalyst modified with nitrogen can significantly improve the electrocatalytic oxidation performance of HMF to FDCA.

Optimization Strategies of Preparation of Biomass-Derived Carbon Electrocatalyst for Boosting Oxygen Reduction Reaction: A Minireview

Oxygen reduction reaction (ORR) has attracted considerable attention for clean energy conversion technologies to reduce traditional fossil fuel consumption and greenhouse gas emissions. Although platinum (Pt) metal is currently used as an electrocatalyst to accelerate sluggish ORR kinetics, the scarce resource and high cost still restrict its further scale-up applications. In this regard, biomass-derived carbon electrocatalysts have been widely adopted for ORR electrocatalysis in recent years owing to their tunable physical/chemical properties and cost-effective precursors. In this minireview, recent advances of the optimization strategies in biomass-derived carbon electrocatalysts towards ORR have been summarized, mainly focusing on the optimization of pore structure and active site. Besides, some current challenges and future perspectives of biomass-derived carbon as high-performance electrocatalysts for ORR have been also discussed in detail. Hopefully, this minireview will afford a guideline for better design of biomass-derived carbon electrocatalysts for ORR-related applications.

Greener Routes to Biomass Waste Valorization: Lignin Transformation Through Electrocatalysis for Renewable Chemicals and Fuels Production

Lignin valorization is essential for biorefineries to produce fuels and chemicals for a sustainable future. Today's biorefineries pursue profitable value propositions for cellulose and hemicellulose; however, lignin is typically used mainly for its thermal energy value. To enhance the profit potential for biorefineries, lignin valorization would be a necessary practice. Lignin valorization is greatly advantaged when biomass carbon is retained in the fuel and chemical products and when energy quality is enhanced by electrochemical upgrading. Though lignin upgrading and valorization are very desirable in principle, many barriers involved in lignin pretreatment, extraction, and depolymerization must be overcome to unlock its full potential. This Review addresses the electrochemical transformation of various lignins with the aim of gaining a better understanding of many of the barriers that currently exist in such technologies. These studies give insight into electrochemical lignin depolymerization and upgrading to value-added commodities with the end goal of achieving a global low-carbon circular economy.

Recent advances in the electrooxidation of biomass-based organic molecules for energy, chemicals and hydrogen production

The recent developments in biomass-derivative fuelled electrochemical converters for electricity or hydrogen production together with chemical electrosynthesis have been reviewed.