Electrocatalytic Hydrogenation Research Articles

Porous N-doped carbon-encapsulated iron as a novel catalyst architecture for the electrocatalytic hydrogenation of benzaldehyde.

Carbon porous materials containing nitrogen functionalities and encapsulated iron-based active sites have been suggested as electrocatalysts for energy conversion, however their applications to the hydrogenation of organic substrates via electrocatalytic hydrogenation (ECH) remain unexplored. Herein, we report on a Fe@C:N material synthesized with an adapted annealing procedure and tested as electrocatalyst for the hydrogenation of benzaldehyde. Using different concentrations of the organic, and electrolysis coupled to gas chromatography experiments, we demonstrate that it is possible to use such architectures for the ECH of unsaturated organics. Potential control experiments show that ECH faradaic efficiencies >70% are possible in acid electrolytes, while maintaining selectivity for the alcohol over the pinacol dimerization product. Estimates of product formation rates and turnover frequency (TOF) values suggest that these carbon-encapsulated architectures can achieve competitive performance in acid electrolytes relative to both base and precious metal electrodes.

An Organic Molecular Mimetic Metal-Free Heterogeneous Catalyst for Electrocatalytic Alkyne Semihydrogenation.

The direct construction of metal-free catalysts on conductive substrates for electrocatalytic organic hydrogenation reactions is significant but still unexplored. Here, learning from the homogeneous molecular catalysts, an organic molecular mimetic metal-free heterogeneous catalyst is designed and constructed in situ on a graphite flake electrode via a mild electrochemical oxidation‒reduction relay strategy. The as-prepared -COOH- and -OH-functionalized metal-free catalyst exhibits an electrocatalytic alkyne semihydrogenation performance with a 72% Faradaic efficiency, 99% selectivity and 96% yield of the alkene product, which is comparable to that of noble metal catalysts. The removal of these oxygen-containing groups leads to negligible activity. The experimental and calculation results reveal that the origin of the high activity can be assigned to the -COOH and -OH groups on graphite. A flow electrolytic cell delivers ten grams of hydrogenated products with 81% Faradaic efficiency. This metal-free catalyst is also suitable for gas-phase acetylene semihydrogenation and other electrocatalytic hydrogenation reactions.

An Organic Molecular Mimetic Metal‐Free Heterogeneous Catalyst for Electrocatalytic Alkyne Semihydrogenation

The direct construction of metal‐free catalysts on conductive substrates for electrocatalytic organic hydrogenation reactions is significant but still unexplored. Here, learning from the homogeneous molecular catalysts, an organic molecular mimetic metal‐free heterogeneous catalyst is designed and constructed in situ on a graphite flake electrode via a mild electrochemical oxidation‒reduction relay strategy. The as‐prepared –COOH‐ and –OH‐functionalized metal‐free catalyst exhibits an electrocatalytic alkyne semihydrogenation performance with a 72% Faradaic efficiency, 99% selectivity and 96% yield of the alkene product, which is comparable to that of noble metal catalysts. The removal of these oxygen‐containing groups leads to negligible activity. The experimental and calculation results reveal that the origin of the high activity can be assigned to the –COOH and –OH groups on graphite. A flow electrolytic cell delivers ten grams of hydrogenated products with 81% Faradaic efficiency. This metal‐free catalyst is also suitable for gas‐phase acetylene semihydrogenation and other electrocatalytic hydrogenation reactions.

Hydrogen Spillover Mechanism at the Metal-Metal Interface in Electrocatalytic Hydrogenation.

Hydrogen spillover in metal-supported catalysts can largely enhance electrocatalytic hydrogenation performance and reduce energy consumption. However, its fundamental mechanism, especially at the metal-metal interface, remains further explored, impeding relevant catalyst design. Here, we theoretically profile that a large free energy difference in hydrogen adsorption on two different metals (|ΔGH-metal(i) - ΔGH-metal(ii)|) induces a high kinetic barrier to hydrogen spillover between the metals. Minimizing the difference in their d-band centers (Δεd) should reduce |ΔGH-metal(i) - ΔGH-metal(ii)|, lowering the kinetic barrier to hydrogen spillover for improved electrocatalytic hydrogenation. We demonstrated this concept using copper-supported ruthenium-platinum alloys with the smallest Δεd, which delivered record high electrocatalytic nitrate hydrogenation performance, with ammonia production rate of 3.45±0.12 mmol h-1 cm-2 and Faraday efficiency of 99.8±0.2 %, at low energy consumption of 21.4 kWh kgamm-1. Using these catalysts, we further achieve continuous ammonia and formic acid production with a record high-profit space.

Hydrogen Spillover Mechanism at the Metal–Metal Interface in Electrocatalytic Hydrogenation

Hydrogen spillover in metal‐supported catalysts can largely enhance electrocatalytic hydrogenation performance and reduce energy consumption. However, its fundamental mechanism, especially at the metal–metal interface, remains further explored, impeding relevant catalyst design. Here, we theoretically profile that a large free energy difference in hydrogen adsorption on two different metals (|ΔGH‐metal(i) − ΔGH‐metal(ii)|) induces a high kinetic barrier to hydrogen spillover between the metals. Minimizing the difference in their d‐band centers (Δεd) should reduce |ΔGH‐metal(i) − ΔGH‐metal(ii)|, lowering the kinetic barrier to hydrogen spillover for improved electrocatalytic hydrogenation. We demonstrated this concept using copper‐supported ruthenium–platinum alloys with the smallest Δεd, which delivered record high electrocatalytic nitrate hydrogenation performance, with ammonia production rate of 3.45±0.12 mmol h−1 cm−2 and Faraday efficiency of 99.8±0.2 %, at low energy consumption of 21.4 kWh kgamm−1. Using these catalysts, we further achieve continuous ammonia and formic acid production with a record high‐profit space.

Electrocatalytic hydrogenation of lignin-derived compounds in heteropolyacid fluidized system

Electrocatalytic hydrogenation of lignin-derived compounds in heteropolyacid fluidized system

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.

Electrocatalytic Acetylene Hydrogenation in Concentrated Seawater at Industrial Current Densities.

Electrocatalytic acetylene hydrogenation to ethylene (E-AHE) is a promising alternative for thermal-catalytic process, yet it suffers from low current densities and efficiency. Here, we achieved a 71.2% Faradaic efficiency (FE) of E-AHE at a large partial current density of 1.0 A cm-2 using concentrated seawater as an electrolyte, which can be recycled from the brine waste (0.96 M NaCl) of alkaline seawater electrolysis (ASE). Mechanistic studies unveiled that cation of concentrated seawater dynamically prompted unsaturated interfacial water dissociation to provide protons for enhanced E-AHE. As a result, compared with freshwater, a twofold increase of FE of E-AHE was achieved on concentrated seawater-based electrolysis. We also demonstrated an integrated system of ASE and E-AHE for hydrogen and ethylene production, in which the obtained brine output from ASE was directly fed into E-AHE process without any further treatment for continuously cyclic operations. This innovative system delivered outstanding FE and selectivity of ethylene surpassed 97.0% and 97.5% respectively across wide-industrial current density range (≤ 0.6 A cm-2). This work provides a significant advance of electrocatalytic ethylene production coupling with brine refining of seawater electrolysis.

Electrocatalytic Acetylene Hydrogenation in Concentrated Seawater at Industrial Current Densities

Electrocatalytic acetylene hydrogenation to ethylene (E‐AHE) is a promising alternative for thermal‐catalytic process, yet it suffers from low current densities and efficiency. Here, we achieved a 71.2% Faradaic efficiency (FE) of E‐AHE at a large partial current density of 1.0 A cm−2 using concentrated seawater as an electrolyte, which can be recycled from the brine waste (0.96 M NaCl) of alkaline seawater electrolysis (ASE). Mechanistic studies unveiled that cation of concentrated seawater dynamically prompted unsaturated interfacial water dissociation to provide protons for enhanced E‐AHE. As a result, compared with freshwater, a twofold increase of FE of E‐AHE was achieved on concentrated seawater‐based electrolysis. We also demonstrated an integrated system of ASE and E‐AHE for hydrogen and ethylene production, in which the obtained brine output from ASE was directly fed into E‐AHE process without any further treatment for continuously cyclic operations. This innovative system delivered outstanding FE and selectivity of ethylene surpassed 97.0% and 97.5% respectively across wide‐industrial current density range (≤ 0.6 A cm−2). This work provides a significant advance of electrocatalytic ethylene production coupling with brine refining of seawater electrolysis.

High‐Density Rare‐Earth Single‐Atom‐Triggered Unconventional Transition of Adsorption Configuration on La1Pd Monatomic Alloy Metallene for Sustainable Electrocatalytic Alkynol Semi‐Hydrogenation

AbstractElectrocatalytic alkynol semi‐hydrogenation for the high‐value chemicals alkenol with mild conditions and carbon‐free emission is a potentially green and sustainable alternative to conventional thermocatalytic routes, which generally involves the design of electrocatalysts with high activity and high selectivity. Here, the rare‐earth single‐atom (Ln = La, Nd, Pr) coordinated Pd metallene (Ln1Pdene) is reported for electrocatalytic 2‐methyl‐3‐butyn‐2‐ol (MBY) semi‐hydrogenation reaction (MBY ESHR) to synthesis of 2‐methyl‐3‐buten‐2‐ol (MBE). Typically, in alkaline medium containing 0.1 m MBY, MBY conversion and MBE selectivity of La1Pdene are as high as ≈97% and ≈95%, respectively, with excellent electrocatalytic stability. Meanwhile, in situ infrared spectra reveal the conversion of MBY to MBE during the dynamic electrocatalytic process. Theoretical calculations reveal that the interaction between La single‐atom and Pd host triggers an unconventional transformation of the intermediate MBE* adsorption configuration during electrocatalytic hydrogenation, achieving the optimal desorption energy between La1Pd and target product and optimizing the reaction energy barriers to inhibit the over‐hydrogenation of MBE. Moreover, La single‐atom as the adsorption active site of the hydrogen supplier H2O effectively reduces the competition adsorption between the reactants MBY and H2O, rendering La single‐atom and Pd host as the synergistic co‐catalytic active sites to promote the electrocatalytic MBY semi‐hydrogenation reaction.

Electrocatalytic Transfer Hydrogenation of 1-Octene with [(tBuPCP)Ir(H)(Cl)] and Water.

Electrocatalytic hydrogenation of 1-octene as non-activated model substrate with neutral water as H-donor is reported, using [(tBuPCP)Ir(H)(Cl)] (1) as the catalyst, to form octane with high faradaic efficiency (FE) of 96% and a kobs of 87 s-1. Cyclic voltammetry with 1 revealed that two subsequent reductions trigger the elimination of Cl- and afford the highly reactive anionic Ir(I) hydride complex [(tBuPCP)Ir(H)]- (2), a previously merely proposed intermediate for which we now report first experimental data by mass spectrometry. In absence of alkene, the stoichiometric electrolysis of 1 in THF with water selectively affords the Ir(III) dihydride complex [(tBuPCP)Ir(H)2] (3) in 88% FE from the reaction of 2 with H2O. Complex 3 then hydrogenates the alkene in classical fashion. The presented electro-hydrogenation works with extremely high FE, because the iridium hydrides are water stable, which prevents H2 formation. Even in strongly alkaline conditions (Bu4NOH added), the electro-hydrogenation of 1-octene with 1 also proceeds cleanly (89% FE), suggesting a highly robust process that may rely on H2O activation, reminiscent to transfer hydrogenation pathways, instead of classical H+ reduction. DFT calculations confirmed oxidative addition of H2O as a key step in this context.

Mechanism of Electrocatalytic H2 Evolution, Carbonyl Hydrogenation, and Carbon-Carbon Coupling on Cu.

Aqueous-phase electrocatalytic hydrogenation of benzaldehyde on Cu leads not only to benzyl alcohol (the carbonyl hydrogenation product), but Cu also catalyzes carbon-carbon coupling to hydrobenzoin. In the absence of an organic substrate, H2 evolution proceeds via the Volmer-Tafel mechanism on Cu/C, with the Tafel step being rate-determining. In the presence of benzaldehyde, the catalyst surface is primarily covered with the organic substrate, while H* coverage is low. Mechanistically, the first H addition to the carbonyl O of an adsorbed benzaldehyde molecule leads to a surface-bound hydroxy intermediate. The hydroxy intermediate then undergoes a second and rate-determining H addition to its α-C to form benzyl alcohol. The H additions occur predominantly via the proton-coupled electron transfer mechanism. In a parallel reaction, the radical α-C of the hydroxy intermediate attacks the electrophilic carbonyl C of a physisorbed benzaldehyde molecule to form the C-C bond, which is rate-determining. The C-C coupling is accompanied by the protonation of the formed alkoxy radical intermediate, coupled with electron transfer from the surface of Cu, to form hydrobenzoin.

Recent developments of single atom alloy catalysts for electrocatalytic hydrogenation reactions

This review discusses the recent developments of single-atom alloy (SAA) catalysts toward CO2, CO, N2, and NO3– hydrogenation reactions in the electrocatalysis context, a natural expansion from the thermal catalysis origin where the concept of SAA was born and validated. Electrocatalytic hydrogenations of CO2, CO, NO3–, and N2 into value-added chemicals offer an attractive general route to mitigate greenhouse gas emissions using renewable energy without H2 feed stream. These reactions typically involve multiple electron-transfer-coupled elementary reaction steps that are of broad relevance to many electrocatalytic applications, making them well-positioned for translational fundamental studies relevant to other emerging electrochemical reactions. While there has been exciting progress in SAA research for various thermal catalytic reactions in the last decade, the design, application, and characterization of SAA catalysts in electrocatalysis remain nascent with intriguing uncertainties and ample opportunities. We highlight the recent research findings in this growing area, where the SAAs, owing to their unique doped metal properties and atomically precise bimetallic synergies, promote selective reaction pathways by tuning binding energies and distributions of adsorbates/intermediates. We also provide our perspective on this growing research area's potential challenges and opportunities.

Electrocatalyst hydrogenation of lignol-derived compounds: Conversion regularity and product selectivity

Phenolic derivatives, crucial components of bio-oil, require thorough understanding of their electrocatalytic hydrogenation (ECH) properties for efficient bio-oil utilization. This study investigated guaiacol, a representative phenolic derivative in bio-oil, focusing on its ECH mechanism, conversion, and product selectivity under varied conditions (temperature: 40–80 °C, perchloric acid concentration: 0.2–1.0 mol/L, current intensity: ((–10)–(–150) mA). Additionally, this study also explored the influence of intermediate products (2-methoxycyclohexanone and cyclohexanone) on both the conversion rate and the selectivity of the products. The experiment had revealed that guaiacol's ECH conversion rate improved with higher temperature and current intensity, whereas an increase in perchloric acid concentration negatively affected the conversion. Significantly, the presence of intermediate products, especially 2-methoxycyclohexanone, markedly enhanced the ECH conversion of guaiacol. Investigating further into the ECH mechanism of other phenolic derivatives, including phenol, pyrocatechol, guaiacol eugenol, and vanillin, as well as their combination, revealed a trend where conversion rates inversely correlated with the complexity of the functional groups on the benzene ring. Specifically, phenol, with its simpler structure, showed the highest conversion rate at 89.34%, in stark contrast to vanillin which, owing to its more complex structure, exhibited the lowest at 46.79%. In our multi-component mixture studies, it was observed that synergistic and competitive interactions significantly alter ECH conversion rates, with some mixtures showing enhanced conversion rate indicative of synergistic effects.

In situ self-assembled bismuth oxide fractals enabling highly selective electrosynthesis of formate in flow cells at high current densities

In this work, we present a scalable in-situ growth strategy for self-assembling a carbon felt supported Bi2O3 fractal nanostructure (f-Bi2O3/CF), enabling superior performance towards electrocatalytic CO2-to-formate conversion with an optimal Faradaic efficiency of 95.1% at −0.9 V (vs. RHE) in flow cell. More impressively, the current density reaches an industrially relevant 235.7 mA cm−2 and remains a high FEformate of 87.7%. The enhanced catalytic activity of the f-Bi2O3/CF model is attributed to the increased adsorption energy of OCHO* intermediate by changing the surface charge distribution according to DFT calculations. Using the aforementioned method, a series of other CF supported metal oxide catalysts (i.e., CuO, In2O3, and SnO2) are easily obtained. A brief techno-economic analysis (TEA) model demonstrates the economic potential of electrocatalytic hydrogenation of CO2 into formate in flow cell. Our findings offer a promising pathway for the fabrication of stable and accessible fractal structure, applicable to a wide range of scenarios.

Deprotonated 2-thiolimidazole serves as a metal-free electrocatalyst for selective acetylene hydrogenation.

Metal-free catalysts offer a desirable alternative to traditional metal-based electrocatalysts. However, metal-free catalysts, featuring defined active sites, rarely show activities as promising as metal-based materials. Here we report 2-thiolimidazole as an efficient metal-free catalyst for selective electrocatalytic hydrogenation of acetylene into ethylene. Under alkaline conditions, the sulfhydryl and imino groups of 2-thiolimidazole are spontaneously deprotonated into dianions. Deprotonation thus enriches the negative charges of pyridinic N sites in 2-thiolimidazole to enhance the adsorption of electrophilic acetylene through the σ-configuration. Ethylene partial current densities show a volcano relationship with the negative charges of the pyridinic N sites in various imidazole derivatives. Consequently, the deprotonated 2-thiolimidazole exhibits an ethylene partial current density and faradaic efficiency competitive with metal-based catalysts like Cu and Pd. This work highlights the tunability and promising potential of metal-free molecules in electrocatalysis.

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.

Efficient electrocatalytic alkyne Semi-Hydrogenation and deuteration using Pd/PANI catalysts supported on nickel foam

In this study, we synthesized Pd/PANI catalysts anchored on nickel foam (NF) via a single-step CV electrodeposition process. The resulting Pd0.3/PANI-NF materials exhibited outstanding selectivity and activity for electrocatalytic alkyne semi-hydrogenation and deuteration under ambient conditions. Characterization of Pd/PANI and control experiment revealed that the combination of PANI and Pd had a synergistic effect on the catalytic performance of Pd/PANI-NF for alkyne semi-hydrogenation. Optimized conditions in H-cells allowed efficient conversion of various terminal and internal alkynes into their corresponding alkenes with remarkable yields up to 92 % and a Faradaic efficiency of 88 %, even at low Pd loading (0.4 mol%). The Pd0.3/PANI-NF showed sustained catalytic activity for gram-scale alkene synthesis through five usage cycles under continuous flow conditions, marked by a high TOF (up to 230 h−1) and combined TONs of 2151, establishing its practical viability for electrocatalytic hydrogenation.

Recent Advancements on Spin Engineering Strategies for Highly Efficient Electrocatalytic Oxygen Evolution Reactions.

Oxygen evolution reaction (OER) is a widely employed half-electrode reaction in oxygen electrochemistry, in applications such as hydrogen evolution, carbon dioxide reduction, ammonia synthesis, and electrocatalytic hydrogenation. Unfortunately, its slow kinetics limits the commercialization of such applications. It is therefore highly imperative to develop highly robust electrocatalysts with high activity, long-term durability, and low noble-metal contents. Previously intensive efforts have been made to introduce the advancements on developing non-precious transition metal electrocatalysts and their OER mechanisms. Electronic structure tuning is one of the most effective and interesting ways to boost OER activity and spin angular momentum is an intrinsic property of the electron. Therefore, modulation on the spin states and the magnetic properties of the electrocatalyst enables the changes on energy associated with interacting electron clouds with radical absorbance, affecting the OER activity and stability. Given that few review efforts have been made on this topic, in this review, the-state-of-the-art research progress on spin-dependent effects in OER will be briefed. Spin engineering strategies, such as strain, crystal surface engineering, crystal doping, etc., will be introduced. The related mechanism for spin manipulation to boost OER activity will also be discussed. Finally, the challenges and prospects for the development of spin catalysis are presented. This review aims to highlight the significance of spin engineering in breaking the bottleneck of electrocatalysis and promoting the practical application of high-efficiency electrocatalysts.

Impact of alloying on electrocatalytic hydrogenation of benzaldehyde over sputtered NiCu film catalysts

In this work, we prepare a series of NiCu alloy film catalysts with different contents by magnetron sputtering to investigate the synergistic effect between Ni and Cu in electrocatalytic hydrogenation of benzaldehyde. The results show that alloying of Ni and Cu can significantly enhance the electrocatalytic activity of benzaldehyde hydrogenation. With the increase of Ni content, the conversion rate of benzaldehyde increases two to three orders of magnitude, and the Faradaic efficiency of the Ni-rich catalysts is higher than that of the Cu-rich catalysts. In addition, the alloy composition affects the relative coverages of H and benzaldehyde, leading to different reaction orders in benzaldehyde. The boosted electrocatalytic activity with the increase of Ni content is in accordance with the electrochemical impedance spectroscopy that increasing Ni content can decrease the charge transfer resistance of the alloy catalysts.