Electrochemical Hydrogenation Research Articles

Buffering Donor Shuttles in Proton-Coupled Electron Transfer Kinetics for Electrochemical Hydrogenation of Hydroxyacetone to Propylene Glycol.

Electrochemical hydrogenation reactions demand rapid proton-coupled electron transfer at the electrode surface, the kinetics of which depend closely on pH. Buffer electrolytes are extensively employed to regulate pH over a wide range. However, the specific role of buffer species should be taken into account when interpreting the intrinsic pH dependence, which is easily overlooked in the current research. Herein, we report the electrochemical hydrogenation of hydroxyacetone, derived from glycerol feedstock, to propylene glycol with a faradaic efficiency of 56 ± 5% on a polycrystalline Cu electrode. The reaction activities are comparable in citrate, phosphate, and borate buffer electrolytes, encompassing different buffer identities and pH. The electrokinetic profile reveals that citrate is a site-blocking adsorbate on the Cu surface, thereby decreasing buffer concentration and increasing pH will enhance the reaction rate; phosphate is an explicit proton donor, which promotes the interfacial rate by increasing buffer concentration and decreasing pH, while borate is an innocent buffer, which can be used to investigate the intrinsic pH effect. Combined with in situ SEIRAS, we demonstrate that water is the primary proton source in citrate and borate electrolytes, reiterating the rationality of the proposed mechanism based on the microkinetic modeling. Our results emphasize the intrinsic complexity of the buffer system on the kinetic activity for electrocatalysis. It calls for special care when we diagnose the mechanistic pathway in buffer electrolytes convoluted by different buffer identities and pH.

Cluster-Level Heterostructure of PMo12/Cu for Efficient and Selective Electrocatalytic Hydrogenation of High-Concentration 5-Hydroxymethylfurfural.

Electrochemical hydrogenation of aldehyde molecules, exemplified by 5-hydroxymethylfurfural (HMF), offers a sustainable approach for synthesizing higher value-added alcohols. However, severe coupling side reactions impede its practical implementation at high concentrations. In this work, a cluster-level heterostructure of a PMo12/Cu catalyst is synthesized by loading Keggin-type phosphomolybdic acid (H3PMo12O40, PMo12) onto Cu nanowires. The catalyst exhibits high selectivity in electrocatalytic hydrogenation (ECH) of HMF to 2,5-bishydroxymethylfuran (BHMF) under an unprecedentedly high substrate concentration of 1.0 M. Under -0.3 V (vs RHE) with 1.0 M HMF, PMo12/Cu shows a Faradaic efficiency as high as 98% with an excellent productivity of 4.35 mmol cm-2 h-1 toward BHMF, much higher than those on the pristine Cu nanowires. Mechanism studies and density functional theory calculations demonstrate that the heterostructural interface of PMo12/Cu serves as an active reaction center for the ECH. The unique electronic properties and geometric structure promote the dissociative reduction of water molecules to generate H* and reduce HMF with a decreased reaction energy barrier, which is responsible for exceptional reactivity and selectivity.

A Comparative Study of Electrochemical Reduction of Levulinic Acid on Various Electrodes in Organic Solvents.

Studies on the electrochemical hydrogenation (ECH) of levulinic acid (LA) to valeric acid (VA) or γ-valerolactone (GVL) have mainly focused on the electrochemical reduction of LA in acidic aqueous solutions. However, the narrow range of applied potentials has hindered understanding of some mechanistic aspects of LA electrochemical conversion. Earlier, we discovered that employing proton-deficient non-aqueous reaction media provides more comprehensive insights into the mechanism of LA electrochemical reduction. Here, we conducted further investigations into the LA electroreduction process using cyclic voltammetry in various organic solvents on a Pt electrode and on various electrode materials in acetonitrile, both with and without the addition of proton donors. The products of the ECH processes were identified using HPLC. The solvent nature, the presence of proton donors, the electrode material, and the applied potential strongly influence the LA electroreduction process. This study reveals that LA, in the presence proton donors, can undergo electrochemical reduction through different pathways, depending on the difference (ΔE1/2) between the reduction half-wave potential of protons and LA on a certain electrode. When the difference is large, the LA reduction is incomplete and the formation of GVL is observed. Under the close reduction potentials of protons and LA, LA can be completely reduced to VA.

Hydrogen-Free Electrochemical Hydrogenation of Unactivated Alkenes under Nickel Catalysis

Hydrogen-Free Electrochemical Hydrogenation of Unactivated Alkenes under Nickel Catalysis

Scalable and Selective Electrochemical Hydrogenation of Polycyclic Arenes.

The reduction of aromatic compounds constitutes a fundamental and ongoing area of investigation. The selective reduction of polycyclic aromatic compounds to give either fully or partially reduced products remains a challenge, especially in applications to complex molecules at scale. Herein, we present a selective electrochemical hydrogenation of polycyclic arenes conducted under mild conditions. A noteworthy achievement of this approach is the ability to finely control both the complete and partial reduction of specific aromatic rings within polycyclic arenes by judiciously varying the reaction solvents. Mechanistic investigations elucidate the pivotal role played by in situ proton generation and interface regulation in governing reaction selectivity. The reductive electrochemical conditions show a very high level of functional-group tolerance. Furthermore, this methodology represents an easily scalable reduction (demonstrated by the reduction of 1 kg scale starting material) using electrochemical flow chemistry to give key intermediates for the synthesis of specific drugs.

Scalable and Selective Electrochemical Hydrogenation of Polycyclic Arenes

Scalable and Selective Electrochemical Hydrogenation of Polycyclic Arenes

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.

Response of hydrogen charging diffusion of the austenitic stainless steel AISI 310s

The subject of hydrogen embrittlement seems to be more and more up-to-date and needed to be explored. World research teams working on this issue have not developed a clear method of preventing this process. The conclusion is that this issue should be approached individually, depending on the type of material, its structure and operating conditions. The problem will escalate in the near future as a result of the planned replacement of the traditional energy sources used so far with hydrogen energy. The paper presents the method of electrochemical hydrogenation, which reflects the conditions of galvanic coating of metallic materials used in the automotive industry. The aim of the research was to determine the influence of the time of hydrogenation on the properties and microstructure of austenitic steel.

Synthesis and electrochemical hydrogenation of RxTb2-xNi17 and Tb2Ni17-yMy phases (R = Y, Zr, La; M = Li, Mg)

Alloys from the regions of existence of the solid solutions RxTb2-xNi17 and Tb2Ni17-yMy were synthesized by arc-melting with further annealing at 400 ºС. Quantitative and qualitative composition of alloys and powders of electrode materials was determined by scanning electron microscopy and energy-dispersive X-ray spectroscopy. The Tb/R/Ni and Tb/Ni/Mg ratio in the samples was confirmed also by X-ray fluorescence spectroscopy. The cell parameters of RxTb2-xNi17 (x = 0.5) ternary phases are: a = 8.2987(9) Å, c = 8.0206(8) Å, V = 478.37(9) Å3 for R = Zr, a = 8.3161(6) Å, c = 8.0482(8) Å, V = 482.03(6) Å3 for R = Y and a = 8.3690(6) Å, c = 8.0560(7) Å, V = 488.66(6) Å3 for R = La. Tb atoms were partially substituted by Y, Zr and La atoms because of closeness of atomic radii size. Under experimental condition capacity parameters were 1.81 H/f.u. for the Zr-containing electrode, 2.29 H/f.u. for the Y-containing electrode and 2.31 H/f.u. for the La-containing electrode. In the case of Li,Mg co-doped electrodes we observed more than 2.5 H/f.u. Cell parameters of the Zr- and La-containing phases after hydrogenation increased isotropically. Synthesized hydrides can be interpreted as superstructures with the Tb2Mn17C2.5-type (filled-up of Th2Ni17). The Y0.5Tb1.5Ni17-based electrode demonstrates the potential corrosion at -0.540 V, electrodes with the compositions Zr0.5Tb1.5Ni17 and La0.5Tb1.5Ni17 show -0.413 V and -0.405 V, respectively. Li and Mg-codoped electrodes shoved the corrosion potential -0.410 V (Tb2Ni16.4Li0.2Mg0.4) and -0.550 V for Tb2Ni15.6Li0.6Mg0.8, respectively.

The Impact of Electron Donating and Withdrawing Groups on Electrochemical Hydrogenolysis and Hydrogenation of Carbonyl Compounds.

The hydrogenolysis or hydrodeoxygenation of a carbonyl group, where the C═O group is converted to a CH2 group, is of significant interest in a variety of fields. A challenge in electrochemically achieving hydrogenolysis of a carbonyl group with high selectivity is that electrochemical hydrogenation of a carbonyl group, which converts the C═O group to an alcohol group (CH-OH), is demonstrated not to be the initial step of hydrogenolysis. Instead, hydrogenation and hydrogenolysis occur in parallel, and they are competing reactions. This means that although both hydrogenolysis and hydrogenation require adding H atoms to the carbonyl group, they involve different intermediates formed on the electrode surface. Thus, revealing the difference in intermediates, transition states, and kinetic barriers for hydrogenolysis and hydrogenation pathways is the key to understanding and controlling hydrogenolysis/hydrogenation selectivity of carbonyl compounds. In this study, we aimed to identify features of reactant molecules that can affect their hydrogenolysis/hydrogenation selectivity on a Zn electrode that was previously shown to promote hydrogenolysis over hydrogenation. In particular, we examined the electrochemical reduction of para-substituted benzaldehyde compounds with substituent groups having different electron donating/withdrawing abilities. Our results show a strikingly systematic impact of the substituent group where a stronger electron-donating group promotes hydrogenolysis and a stronger electron-withdrawing group promotes hydrogenation. These experimental results are presented with computational results explaining the substituent effects on the thermodynamics and kinetics of electrochemical hydrogenolysis and hydrogenation pathways, which also provide critically needed information and insights into the transition states involved with these pathways.

Electrochemical and catalytic conversion of CO2 into formic acid on Cu-InO2 nano alloy decorated on reduced graphene oxide (Cu-InO2@rGO)

The catalytic and electrochemical hydrogenation of CO2 offers the option of a carbon-neutral cycle for sustainable energy and synthesis of value-added chemicals. The synthesized noble metal-free Cu-InO2@rGO nanocomposite has been characterized by various techniques such as scanning electron microscopy (SEM) confirming the spherical shape of Cu-InO2 nanoalloy embedded on rGO, the average size calculated by high resolution-transmission electron microscopy (HR-TEM) shows Cu-InO2 (∼ 4 nm) alloy is on rGO surface (∼100 nm). The XRD pattern confirms the Face centered cubic (FCC) crystal structure of Cu-InO2@rGO, and Furrier transform- Infrared (FT-IR) and X-ray photoelectron spectroscopy (XPS) analyses of Cu-In-O exist in the nanomaterials. The linear sweep voltammetry (LSV) demonstrates an ultra-low potential of −0.9 V vs. SCE. The bulk electrolysis on Cu-InO2@rGO electrocatalyst demonstrated at a potential of −1.1 V vs. SCE to reach HCOOH with a Faradic yield of 76.10%. Electrochemical CO2 reduction on Cu-InO2@rGO is responsible for the variation of adsorption of CO2 intermediates due to controlled selectivity and inhibiting the formation of H2 and CO. In catalytic hydrogenation used as the same catalyst was found, an excellent yield towards HCOOH is 5.5 mmol. Current studies have highlighted the enhancement in activity along with selectivity for product formation could be due to having a capable active interface from electrocatalysts for low cost and proficient production of fuels.

Mesoporous Palladium Catalyst for Efficient Electrochemical Semi‐Hydrogenation of Alkynes

AbstractDeveloping robust electrocatalysts for efficient semi‐hydrogenation of alkynes to markedly important alkenes is highly desirable in both research and industry areas. In this work, it is reported that robust palladium mesoporous nanospheres (Pd MSs) with electron‐rich active sites perform perfectly as cathode electrocatalyst for electrochemical semi‐hydrogenation of alkynes in water. In comparison to its counterparts, Pd MSs hold remarkable conversion (97%), superior selectivity (98%), good operation stability in selective semi‐hydrogenation of p‐aminophenylene. High performance is assigned to electron‐rich Pd sites within mesopores that not only favor the formation of active H* but also accelerate the desorption of p‐aminostyrene. Meanwhile, Pd MSs are also highly efficient in selective semi‐hydrogenation of various terminal alkynes with different substituents. It is thus expected that robust Pd MSs can be demonstrated as an alternative catalyst design paradigm for other electrochemical hydrogenation reactions.

Electrocatalytic hydrogenation of acetonitrile to ethylamine in acid

Electrochemical hydrogenation of acetonitrile based on well-developed proton exchange membrane electrolyzers holds great promise for practical production of ethylamine. However, the local acidic condition of proton exchange membrane results in severe competitive proton reduction reaction and poor selection toward acetonitrile hydrogenation. Herein, we conduct a systematic study to screen various metallic catalysts and discover Pd/C exhibits a 43.8% ethylamine Faradaic efficiency at the current density of 200 mA cm−2 with a specific production rate of 2912.5 mmol g−1 h−1, which is about an order of magnitude higher than the other screened metal catalysts. Operando characterizations indicate the in-situ formed PdHx is the active centers for catalytic reaction and the adsorption strength of the *MeCH2NH2 intermediate dictates the catalytic selectivity. More importantly, the theoretical analysis reveals a classic d-band mediated volcano curve to describe the relation between the electronic structures of catalysts and activity, which could provide valuable insights for designing more effective catalysts for electrochemical hydrogenation reactions and beyond.

Electrochemical Nickel-Catalyzed Hydrogenation.

Olefin hydrogenation is one of the most important transformations in organic synthesis. Electrochemical transition metal-catalyzed hydrogenation is an attractive approach to replace the dangerous hydrogen gas with electrons and protons. However, this reaction poses major challenges due to rapid hydrogen evolution reaction (HER) of metal-hydride species that outcompetes alkene hydrogenation step, and facile deposition of the metal catalyst at the electrode that stalls reaction. Here we report an economical and efficient strategy to achieve high selectivity for hydrogenation reactivity over the well-established HER. Using an inexpensive and bench-stable nickel salt as the catalyst, this mild reaction features outstanding substrate generality and functional group compatibility, and distinct chemoselectivity. In addition, hydrodebromination of alkyl and aryl bromides could be realized using the same reaction system with a different ligand, and high chemoselectivity between hydrogenation and hydrodebromination could be achieved through ligand selection. The practicability of our method has been demonstrated by the success of large-scale synthesis using catalytic amount of electrolyte and a minimal amount of solvent. Cyclic voltammetry and kinetic studies were performed, which support a NiII/0 catalytic cycle and the pre-coordination of the substrate to the nickel center.

Electrochemical Hydrogenation of Aliphatic Aldehydes and Acids using Pentlandite Catalysts

AbstractElectrochemical hydrogenations are considered a sustainable alternative to classical thermocatalytic processes prevalent in industrial conversions. Using a base metal sulfide of the pentlandite class, the hydrogenation of glutaraldehyde and propionic acid was investigated. While propionic acid could not be converted, glutaraldehyde was conveniently transformed to the semi‐ and fully hydrogenated products 5‐hydroxypentanal and 1,5‐pentanediol with a partial current density of up to 34 mA cm−2 and a Faraday efficiency of 34 %. Crucial factors for a stable and efficient reaction were found to be the use of an appropriate buffer, avoidance of low pH and the used membrane type. The reaction was implemented into a zero‐gap cell reaching a single pass conversion of up to 22 %, underlining the potential for future application.

In Situ Reconstruction to Surface Sulfide Adsorbed Metal Scaffold for Enhanced Electrocatalytic Hydrogen Evolution Activity

AbstractTransition‐metal‐based compounds have been intensively explored as efficient electrocatalysts for hydrogen evolution reaction (HER). Feasible reconstruction to the real active sites, which is yet to be identified, endows the promotion of HER activity. Here, it is reported that the incoming S coordinates and anion vacancies prompt the structural reconstruction of S‐doped Co3O4 on carbon cloth (S‐Co3O4/CC) during HER. A list of in situ studies reveals that the real active sites for HER are the “metallic surface‐adparticles” system embracing metallic Co scaffold and the dilute coverage of S coordinated Coδ+. Reaction mechanism exploration illustrates that interfacial perimeters between the coverage of Co3S4 moieties and metallic Co considerably facilitate the adsorption of H*, improve the kinetics of water dissociation, and consequently promote HER activity. The exemplified sulfide‐mediated topotactic transformation strategy is extended to the preparation of S, Fe codoped Ni(OH)2 (S‐NiFe/CC) as a bifunctional electrocatalyst. The assembled anion exchange membrane water electrolyzer achieves a current density of 1.0 A cm−2 at 1.72 V, showing excellent capability in catalyzing overall water splitting at ampere level. This study, showing a feasible strategy that enables the facile reconstruction to identify active sites, would inspire the development of efficient electrocatalysts for HER and other electrochemical hydrogenation reaction.

Electrochemical hydrogenation and oxidation of organic species involving water.

Fossil fuel-driven thermochemical hydrogenation and oxidation using high-pressure H2 and O2 are still popular but energy-intensive CO2-emitting processes. At present, developing renewable energy-powered electrochemical technologies, especially those using clean, safe and easy-to-handle reducing agents and oxidants for organic hydrogenation and oxidation reactions, is urgently needed. Water is an ideal carrier of hydrogen and oxygen. Electrochemistry provides a powerful route to drive water splitting under ambient conditions. Thus, electrochemical hydrogenation and oxidation transformations involving water as the hydrogen source and oxidant, respectively, have been developed to be mild and efficient tools to synthesize organic hydrogenated and oxidized products. In this Review, we highlight the advances in water-participating electrochemical hydrogenation and oxidation reactions of representative organic molecules. Typical electrode materials, performance metrics and key characterization techniques are firstly introduced. General electrocatalyst design principles and controlling the microenvironment for promoting hydrogenation and oxygenation reactionsinvolving waterare summarized. Furthermore, paired hydrogenation and oxidation reactions are briefly introduced before finally discussing the challenges and future opportunities of this research field.

Electroplated Electrodes for Continuous and Mass-Efficient Electrochemical Hydrogenation.

Electrocatalytic hydrogenations (ECH) enable the reduction of organic substrates upon usage of electric current and present a sustainable alternative to conventional processes if green electricity is used. Opposed to most current protocols for electrode preparation, this work presents a one-step binder- and additive-free production of silver- and copper-electroplated electrodes. Controlled adjustment of the preparation parameters allows for the tuning of catalyst morphology and its electrochemical properties. Upon optimization of the deposition protocol and carbon support, high faradaic efficiencies of 93 % for the ECH of the Vitamin A- and E-synthon 2-methyl-3-butyn-2-ol (MBY) are achieved that can be maintained at current densities of 240 mA cm-2 and minimal catalyst loadings of 0.2 mg cm-2, corresponding to an unmatched production rate of 1.47 kgMBE gcat -1 h-1. For a continuous hydrogenation process, the protocol can be directly transferred into a single-pass operation mode giving a production rate of 1.38 kgMBE gcat -1 h-1. Subsequently, the substrate spectrum was extended to a total of 17 different C-C-, C-O- and N-O-unsaturated compounds revealing the general applicability of the reported process. Our results lay an important groundwork for the development of electrochemical reactors and electrodes able to directly compete with the palladium-based thermocatalytic state of the art.

Enhanced Electrochemical Hydrogenation of Benzaldehyde to Benzyl Alcohol on Pd@Ni-MOF by Modifying the Adsorption Configuration.

Electrocatalytic hydrogenation (ECH) approaches under ambient temperature and pressure offer significant potential advantages over thermal hydrogenation processes but require highly active and efficient hydrogenation electrocatalysts. The performance of such hydrogenation electrocatalysts strongly depends not only on the active phase but also on the architecture and surface chemistry of the support material. Herein, Pd nanoparticles supported on a nickel metal-organic framework (MOF), Ni-MOF-74, are prepared, and their activity toward the ECH of benzaldehyde (BZH) in a 3 M acetate (pH 5.2) aqueous electrolyte is explored. An outstanding ECH rate up to 283 μmol cm-2 h-1 with a Faradaic efficiency (FE) of 76% is reached. Besides, higher FEs of up to 96% are achieved using a step-function voltage. Materials Studio and density functional theory calculations show these outstanding performances to be associated with the Ni-MOF support that promotes H-bond formation, facilitates water desorption, and induces favorable tilted BZH adsorption on the surface of the Pd nanoparticles. In this configuration, BZH is bonded to the Pd surface by the carbonyl group rather than through the aromatic ring, thus reducing the energy barriers of the elemental reaction steps and increasing the overall reaction efficiency.

Indirect H2O2 synthesis without H2

Industrial hydrogen peroxide (H2O2) is synthesized using carbon-intensive H2 gas production and purification, anthraquinone hydrogenation, and anthrahydroquinone oxidation. Electrochemical hydrogenation (ECH) of anthraquinones offers a carbon-neutral alternative for generating H2O2 using renewable electricity and water instead of H2 gas. However, the H2O2 formation rates associated with ECH are too low for commercialization. We report here that a membrane reactor enabled us to electrochemically hydrogenate anthraquinone (0.25 molar) with a current efficiency of 70% at current densities of 100 milliamperes per square centimeter. We also demonstrate continuous H2O2 synthesis from the hydrogenated anthraquinones over the course of 48 h. This study presents a fast rate of electrochemically-driven anthraquinone hydrogenation (1.32 ± 0.14 millimoles per hour normalized per centimeter squared of geometric surface of electrode), and provides a pathway toward carbon-neutral H2O2 synthesis.