Rh-dispersed Cu nanowire catalyst for boosting electrocatalytic hydrogenation of 5-hydroxymethylfurfural

Electrocatalytic conversion of 5-hydroxymethylfurfural to 5-methyl-2-furanmethanol by delocalization state-tuned bond cleavage

The electrocatalytic conversion of 5-hydroxymethylfurfural (HMF) represents a green strategy for valorizing biomass-derived platform molecules into renewable fuels and value-added chemicals. However, most current electrocatalysts focus on reducing HMF to 2,5-furandimethanol (BHMF), while the selective reduction of HMF into 5-methyl-2-furanmethanol (MFA) in neutral electrolytes has received much less progress. In this work, we developed a Cu3Ge intermetallic catalyst to modulate the electronic properties of Cu. Compared to pure Cu with the BHMF selectivity, the introduction of Ge atoms enhances the electron localization on the Cu lattice, facilitating the preferential CO bond cleavage and promoting the selective formation of MFA. The Cu3Ge catalyst demonstrated an enhanced MFA selectivity of 27% ± 4%, suggesting a potential strategy for tuning electrocatalyst properties to achieve different reduction products.

Manipulation of Hydrogen Transfer Behaviors by RhCu Alloying Enables an All-in-one Sustainable "Furfural-Nitrate" System

Nitrate and furfural are typical wastes mainly from industrialization and agriculturalization progresses, and their clean conversions are still very challenging for a sustainable future. Nevertheless, scant attention has been devoted to the core issues: the rational integration of two wastes recycling and the targeted manipulation of hydrogen (H*) transfer behaviors to address their sluggish reaction kinetics. Herein, we report an all-in-one electrochemical energy system that is thermodynamically designed by coupling nitrate reduction (NO3RR) and furfural oxidation reactions (FORs) together. Particularly, the poor kinetics for both electrode reactions are efficaciously optimized by the bifunctional electrocatalyst of RhCu alloy nanowires on copper foam (RhCu NW/CF) with highly improved dual-directional H*-modulation performances, thus initializing NO3RR for NH3 synthesis at +0.31 V and driving FOR for H2 harvest at an onset potential lower than 0 V. Eventually, such integrated "Furfural-Nitrate" system can simultaneously effectuate the electricity energy supply (10.76 mW cm-2), wastewater purification, cathodic hydrogen storage (NH3), anodic H2 production, and biomass upgrading. Hence, it provides a promising perspective of "turning waste into treasure" in a rational manner, justifying its all-in-one property in addressing the global challenge of sustainable energy.

Internal lattice oxygen sites invert product selectivity in electrocatalytic alkyne hydrogenation over copper catalysts

Copper-based catalysts exhibit excellent performance of electrocatalytic alkynes hydrogenation, especially for the selective alkynes hydrogenation toward alkenes. However, the selective electrocatalytic alkynes hydrogenation toward alkanes is hard to achieve over copper-based catalysts because electron-rich Cu0 sites are unable to adsorb and activate nucleophilic alkenes. Herein, we report a metallic copper catalyst containing internal lattice oxygen atoms for steering the selectivity of alkynes hydrogenation toward alkanes. Internal lattice oxygen atoms protect Cuδ+ sites from being reduced during electrocatalytic alkynes hydrogenation so that alkenes intermediates can continually be adsorbed and converted to alkanes on stable Cuδ+ sites. Due to the synergy between Cu0 and Cuδ+ sites, metallic copper electrocatalyst containing internal lattice oxygen atoms shows an excellent selectivity for selective alkynes hydrogenation toward alkanes (2-methyl-3-butan-2-ol selectivity of 94.9%). This work opens a avenue for steering the selective alkynes hydrogenation, and more importantly, it fills in a gap on the selective electrocatalytic alkynes hydrogenation toward alkanes over copper-based catalysts.

Pairing Electrocatalytic Reduction and Oxidation of Biomass-Derived 5-Hydroxymethylfurfural into Highly Value-Added Chemicals

Simultaneous electrocatalytic reduction and oxidation of 5-hydroxymethylfurfural (HMF) is crucial for biomass refineries. Herein, we report the unprecedentedly high efficiency of the nearly complete conversion of biomass-derived HMF to value-added products, achieving >95% selectivity at -0.4 V vs RHE by pairing electrocatalytic reduction and oxidation (PERO) reactions in a single electrochemical cell. At the cathode, we achieved 99% conversion of HMF to 2,5-dihydroxymethylfuran (DHMF) in ∼99% yield under mild conditions using a PtRu alloy. At the anode, we observed 99% conversion of HMF, nearly perfect selectivity for the oxidative product 2,5-furandicarboxylic acid (FDCA), and 100% Faradaic efficiency on a NiCo(OOH) x nanosheets electrode. The kinetic isotope effect demonstrated that the rate-controlled step was a proton-independent electron transfer process, with minimal impact from substrate concentration variations. After assembling the synchronous reaction cell, the PERO of HMF generated high yields of DHMF (94%) and FDCA (86%), achieving a combined electron efficiency of 131%, nearly doubling the performance of uncoupled cells. This superior performance was attributed to the efficient generation of H* on the PtRu alloy for reduction, alongside the OH* active sites on the NiCo(OOH) x nanosheets electrode for oxidation. This research provides a promising strategy for the sustainable electrocatalytic upgrading of biomass-derived chemicals.

Boosting Electrocatalytic Hydrogenation of Phenylacetylene via Accelerating Water Electrolysis on a Cr-Cu2O Surface

Electrochemical alkyne reduction with H2O as a hydrogen source represents a sustainable route for value-added olefin production. However, the reaction efficiency is hampered by the high voltage and low activity of Cu electrodes due to their weak adsorbed hydrogen (*H) generation property. In this article, we present the enhanced electrocatalysis of phenylacetylene to styrene over a highly dispersive Cr-doped Cu2O nanowire (Cr-Cu2O) cathode. The Cr-Cu2O demonstrates improved catalytic activity compared to pure Cu2O, achieving a high conversion of about 94.7% and a selectivity of 87.9% with a Faraday efficiency of 64.5% at a low potential of -1.15 V vs Hg/HgO. The combination of electrochemical characterization techniques and theoretical calculations demonstrated the key role of introduced Cr atoms in lowering the activation energy barrier of surface water electrolysis to *H and facilitating the adsorption of phenylacetylene, which promotes the effective hydrogenation of phenylacetylene with *H via an electrocatalytic hydrogenation mechanism. In short, this work provides a feasible strategy to enrich interfacial *H, thus improving the semihydrogenation performance of phenylacetylene.

A Cosolvent Electrolyte Boosting Electrochemical Alkynol Semihydrogenation

Green electricity-driven alkenol electrosynthesis via electrocatalytic alkynol semihydrogenation represents a sustainable route to conventional thermocatalysis. Both the electrocatalyst and electrolyte strongly impact the semihydrogenation performance. Despite significant progress in developing sophisticated electrocatalysts, a well-designed electrolyte in conjunction with industrial catalysts is an attractive strategy to advance the industrialization process of electrocatalytic alkynol semihydrogenation, but remains unexplored. Here, we develop a dimethyl sulfoxide (DMSO)-H2O cosolvent electrolyte for electrocatalytic alkynol semihydrogenation. At an alkynol conversion of about 100%, the DMSO-H2O electrolyte compared to the DMSO-free counterpart enables the alkenol selectivity on Cu catalysts to be promoted from 60-70% to over 90% at all measured current densities; meanwhile, the reaction rate is slightly decreased due to the inhibited water dissociation. Mechanistic studies reveal that the strong hydrogen-bond interactions between DMSO and H2O suppress the dissociation of interfacial H2O, leading to a decreased H* coverage at the electrode surface. The decreased H* coverage hinders the overhydrogenation of alkynols and favors the production of alkenols. Remarkably, the DMSO-induced enhancement of alkenol selectivity is applicable to a set of commercial catalysts and to the semihydrogenation of various alkynols. Eventually, a scaled-up 3 × 100 cm2 electrolyzer stack is established to achieve an alkynol conversion of ∼96% and an alkenol selectivity of ∼95% in the cosolvent electrolyte. This work not only presents an electrolyte strategy for boosting alkenol electrosynthesis, but also highlights the possibility of sustainable alkenol electro-production.

Introducing Fe Into Cu-Based Catalyst to Boost Electrocatalytic Hydrogenation of 5-Hydroxymethylfurfural

Converting biomass-derived 5-hydroxymethylfurfural (HMF) into high-valued 2,5-dihydroxymethylfurfural (DHMF) via electrocatalytic hydrogenation (ECH) technology has been widely regarded as one of the most economical and eco-friendly routes. The high selectivity and activity depend on the reasonable regulation of the adsorption and activation of adsorbed hydrogen (H*) and HMF on the surface of the electrocatalyst. Herein, we report nanoflower-like CuFe-based electrocatalysts on copper foam (CF) substrates (CuFeOx/CF). DHMF was achieved on the optimal CuFeOx/CF with a selectivity of 93.3 % and a yield of 90.1 %. The H*, HMF and product were observed by in situ attuned total reflection Fourier transform infrared spectroscopy (ATR-FTIR). Moreover, in situ Raman spectra discloses the reconstruction of catalyst into CuFe-bimetal with low valence state. Density functional theory (DFT) calculations demonstrate that introducing Fe plays a role in regulating the electronic structure of Cu sites, which facilitate the generation of H* and adsorption of HMF, thus hampering the occurrence of dimerization. This study provides an innovative idea for the rational design of non-precious bimetallic electrocatalysts for ECH to produce high-valued chemicals.

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.

Surfactant Directionally Assembled at the Electrode-Electrolyte Interface for Facilitating Electrocatalytic Aldehyde Hydrogenation

Electrocatalytic hydrogenation of unsaturated aldehydes to unsaturated alcohols is a promising alternative to conventional thermal processes. Both the catalyst and electrolyte deeply impact the performance. Designing the electrode-electrolyte interface remains challenging due to its compositional and structural complexity. Here, we employ the electrocatalytic hydrogenation of 5-hydroxymethylfurfural (HMF) as a reaction model. The typical cationic surfactant, cetyltrimethylammonium bromide (CTAB), and its analogs are employed as electrolyte additives to tune the interfacial microenvironment, delivering high-efficiency hydrogenation of HMF and inhibition of the hydrogen evolution reaction (HER). The surfactants experience a conformational transformation from stochastic distribution to directional assembly under applied potential. This oriented arrangement hampers the transfer of water molecules to the interface and promotes the enrichment of reactants. In addition, near 100 % 2,5-bis(hydroxymethyl)furan (BHMF) selectivity is achieved, and the faradaic efficiency (FE) of the BHMF is improved from 61 % to 74 % at -100 mA cm-2. Notably, the microenvironmental modulation strategy applies to a range of electrocatalytic hydrogenation reactions involving aldehyde substrates. This work paves the way for engineering advanced electrode-electrolyte interfaces and boosting unsaturated alcohol electrosynthesis efficiency.

Alloying and confinement effects on hierarchically nanoporous CuAu for efficient electrocatalytic semi-hydrogenation of terminal alkynes

Electrocatalytic alkynes semi-hydrogenation to produce alkenes with high yield and Faradaic efficiency remains technically challenging because of kinetically favorable hydrogen evolution reaction and over-hydrogenation. Here, we propose a hierarchically nanoporous Cu50Au50 alloy to improve electrocatalytic performance toward semi-hydrogenation of alkynes. Using Operando X-ray absorption spectroscopy and density functional theory calculations, we find that Au modulate the electronic structure of Cu, which could intrinsically inhibit the combination of H* to form H2 and weaken alkene adsorption, thus promoting alkyne semi-hydrogenation and hampering alkene over-hydrogenation. Finite element method simulations and experimental results unveil that hierarchically nanoporous catalysts induce a local microenvironment with abundant K+ cations by enhancing the electric field within the nanopore, accelerating water electrolysis to form more H*, thereby promoting the conversion of alkynes. As a result, the nanoporous Cu50Au50 electrocatalyst achieves highly efficient electrocatalytic semi-hydrogenation of alkynes with 94% conversion, 100% selectivity, and a 92% Faradaic efficiency over wide potential window. This work provides a general guidance of the rational design for high-performance electrocatalytic transfer semi-hydrogenation catalysts.

Switchable selectivity to electrocatalytic reduction of furfural over Cu2O-derived nanowire arrays

Electrocatalytic reduction of biomass-derived furan compounds provides a green and sustainable approach to produce value-added fuels and chemicals. Despite the achievements in unimolecular transformation, C-C coupling which holds great promise to yield precursors for high-density fuels has not received extensive attention. Herein, we report a Cu2O-derived nanowire array material with switchable selectivity to electrocatalytic reduction of furfural depending on the electrolyte pH. Besides a high selectivity of 98.4% to furfuryl alcohol via hydrogenation at pH 9.5, the Cu2O-derived array structure also exhibits a high selectivity of 83.5% to hydrofuroin via C-C coupling at pH 14. Upon control experiments and detailed characterization of the electrodes, the array architecture is proposed to decrease the diffusion of ketyl radicals which are the key intermediates for C-C coupling. The confined diffusion results in a high local concentration of the radicals in the array and facilitates their collision for enhancing the formation of hydrofuroin.

N-CoFeP/NF electrocatalyst for coupling hydrogen production and oxidation reaction of various alcohols

Replacing the oxygen evolution reaction with the alcohols oxidation reaction (AOR) in electrolytic water is not only expected to reduce the overall energy consumption, but also realize the green synthesis of high value-added chemicals. However, designing high-activity electrocatalysts toward AOR yet faces a daunting challenge due to the indefinite conversion mechanism of different alcohols. Herein, a self-supported N-CoFeP/NF electrocatalyst on a nickel foam is synthesized via hydrothermal method, followed by low temperature nitriding and phosphating. The N-CoFeP/NF exhibits a fine nanorod nanostructure and high crystallinity. The AOR using N-CoFeP/NF catalysts requires a significantly lower potential (1.38-1.42 V vs. RHE) at 100 mA cm-2, reducing the energy input and the improvement of the overall efficiency. Moreover, alcohols with secondary hydroxyl groups located in the middle of the carbon chain underwent CC bond breakage during oxidation, yielding primarily formic acid (FE = 74 %) and acetic acid (FE = 50 %), which exhibits more attractive performance than alcohols with primary hydroxyl groups located at the end group did not undergo chemical bond breakage at a high current density of 400 mA cm-2. This study provides a novel and effective method to design TMPs and the selection of alcohols for anodic reaction, which can be used as a versatile strategy to improve the performance of anodic AOR coupled hydrogen evolution.