Electrocatalytic Hydrogenation Research Articles

Electrocatalytic deep hydrogenation of 4-chlorophenol into cyclohexanol on microchannel-enhanced Ru/TiO2 for wastewater detoxification and simultaneous resource recovery

Chlorophenols (CPs) are among the most significant environmental concerns worldwide, which pose a serious threat to global water safety and human health. Herein, a novel electrocatalytic hydrogenation (ECH) pathway was proposed for the detoxification of CPs, where both the cleavage of C−Cl bond and hydrogenation of phenol ring take place. Employing a fibrous Ru/TiO2 electrode (f-Ru/TiO2) with massive microchannels, we achieved over 99.8% removal of 1 mM 4-chlorophenol (4-CP) within 60 min, with a corresponding kinetic constant of 0.101 min−1. The toxic 4-CP was completely transformed into cyclohexanol, which possesses almost no biotoxicity and could be rapidly recovered from treated water. The ECH system exhibited high 4-CP removal efficiencies at different pH conditions (3−11). Besides, a 4-CP removal efficiency of over 99.1% was achieved even at a remarkably high concentration (10 mM). Mechanism analysis confirms that direct electron transfer dominates the ECH process, while the contribution of atomic hydrogen (H*) is less prominent. Overall, this study demonstrates an inspiring ECH approach with enhanced pollutants diffusion and electron transfer for not only the detoxification of but also resource recovery from chlorophenol wastewater.

Frontispiece: Advances in Selective Electrocatalytic Hydrogenation of Alkynes to Alkenes

Graphical Abstract Selective electrocatalytic alkyne hydrogenation (EAH) is a promising alternative to traditional thermocatalytic hydrogenation for the purification of crude gaseous alkenes and the synthesis of fine chemicals. In this review, combining with the understandings on EAH mechanisms, the key development of EAH electrocatalysts and electrolyzers was systematically discussed. More information can be found in the Review article by J. Zhang and co-workers. (DOI: 10.1002/chem.202202979)

Time and Potential‐Resolved Comparison of Copper Disc and Copper Nanoparticles for Electrocatalytic Hydrogenation of Furfural

Herein, a comparative analysis of two case example catalysts for electrocatalytic hydrogenation (ECH) of furfural under acidic conditions, namely a copper polycrystalline disc and copper nanoparticles dispersed on carbon support, is performed. To gain a detailed insight on ECH trends, a task‐specific methodology is employed based on electrochemistry–mass spectrometry coupling, which enabled time‐ and potential‐resolved detection of volatile ECH products, i.e., 2‐methylfurane (2‐MF) and H2. In this way, the ability to elucidate potential‐dependent product distribution for the two catalysts, namely faradaic efficiency, is achieved. Accordingly, the nanoparticulate analog is significantly more active toward competitive hydrogen evolution reaction and 2‐MF production, whereas the polycrystalline sample is more selective toward furfuryl alcohol. The observed differences in ECH are ascribed to alterations in surface domains, which is supported by surface‐sensitive lead underpotential deposition characterization.

Promoting Electrocatalytic Hydrogenation of Oxalic Acid to Glycolic Acid via an Al3+ Ion Adsorption Strategy Coupled with Ethylene Glycol Oxidation

Electrocatalytic hydrogenation (ECH) of oxalic acid (OX) to produce glycolic acid (GA), an important building block of biodegradable polymers as well as application in various branches of chemistry, has attracted extensive attention in the industry, while it still encounters challenges of low reaction rate and selectivity. Herein, we reported a cation adsorption strategy to realize the efficient ECH of OX to GA by adsorbing Al3+ ions on an anatase titanium dioxide (TiO2) nanosheet array, achieving 2-fold enhanced GA productivity (1.3 vs 0.65 mmol cm-2 h-1) with higher Faradaic efficiency (FE) (85 vs 69%) at -0.74 V vs RHE. We reveal that the Al3+ adatoms on TiO2 both act as electrophilic adsorption sites to enhance the carbonyl (C═O) adsorption of OX and glyoxylic acid (intermediate) and also promote the generation of reactive hydrogen (H*) on TiO2, thus promoting the reaction rate. This strategy is demonstrated effective for different carboxylic acids. Furthermore, we realized the coproduction of GA at the bipolar of a H-type cell by pairing ECH of OX (at cathode) and electrooxidation of ethylene glycol (at anode), demonstrating an economical manner with maximum electron economy.

Catalytic and Electrocatalytic Hydrogenation of Nitroarenes

Functionalized aniline, as an important class of intermediates in industrial production, is in increasing demand in the course of rapid industrial and economic development. Hydrogenation of nitroarenes with low prices and wide sources to produce aniline is one of the most important means. Among them, catalytic hydrogenation is currently the dominant industrial production method in this field, while the electrocatalytic hydrogenation driven by renewable energy power generation is more promising in the context of current sustainable development. Aiming at the problems existing in the industrial production of nitroarene hydrogenation, this Review first sorts out the development process of relevant catalysts mainly from the two aspects of improving selectivity and reducing costs. Then, we have also compiled in situ characterizations and theoretical calculations for related mechanistic studies as well as a class of soluble redox mediators that can facilitate the electrochemical hydrogenation process. Finally, some of the issues that still need to be addressed in this research field are discussed, and several directions that may be feasible are proposed.

Electrocatalytic dual hydrogenation of organic substrates with a Faradaic efficiency approaching 200%

Electrocatalytic dual hydrogenation of organic substrates with a Faradaic efficiency approaching 200%

Modulation of Lewis and Brønsted acid centers with oxygen vacancies for Nb2O5 electrocatalysts: Towards highly efficient simultaneously electrochemical ozone and hydrogen peroxide production

Assembling two desirable half-reactions of green oxidants hydrogen peroxide (H2O2) and ozone (O3) into efficient paired electrolysis is highly valuable in terms of efficiency and environmental-friendliness. However, rational design and construction of electrocatalysts with regulable active sites for the paired electrosynthesis of green oxidants of H2O2 and O3 remain a significant challenge. Herein, A new strategy was developed for tunning the active sites of pseudo-hexagonal centers (TT, Lewis acid sites) and orthogonal centers (T, Brønsted acid sites) in Mxene layered structure niobium pentoxide (Nb2O5) with abundant oxygen vacancy (OV) for the paired electrolysis of 2e- oxygen reduction reaction (ORR) and electrochemical ozone production (EOP). The TT-300 and T-400 electrocatalysts exhibited outstanding electrochemical activity of 2e- ORR (H2O2 selectively of 92% at 0.4 VRHE) and EOP (gaseous ozone FE of 13% at 50 mA cm−2), respectively. The excellent performance was mainly attributed to the TT-300 (Lewis acid sites) and T-400 (Brønsted acid sites) with abundant OV that improve the oxygen-containing intermediates formation of OOH* and deprotonation of water. In addition, the in-situ electro-degradation of organic compounds experiments indicated that the synergistic degradation of O3 and H2O2 possessed a faster kinetic constant compared with a single electrolysis system of O3 and H2O2. The work provides meaningful insights into the rational design and construction of advanced solid acid electrocatalysts for efficient simultaneously electrocatalytic hydrogenation and oxidation to produce green oxidants of O3 and H2O2.

High-performance bimetallic In-Pb for electrocatalytic hydrogenation of levulinic acid

The challenge in the electrochemical reduction of levulinic acid (LA) lies in designing highly selective, energy-efficient, and non-precious-metal electrocatalysts that minimize the competitive hydrogen evolution reaction during LA conversion. Herein, we reported a facile pulsed electrodeposition strategy to fabricate bimetallic electrocatalysts with different combinations of lead (Pb), indium (In), tin, and cadmium supported by free-standing carbon felts (CFs). The as-prepared bimetallic self-supporting electrodes were examined for the electrochemical hydrogenation (ECH) of LA. The resulting InPb/CF electrocatalysts showed superior performance among the bimetallic catalysts. In addition, it was demonstrated that the catalytic performance of bimetallic samples was better than that of the corresponding monometallic samples. Notably, the In72.4Pb27.6/CF exhibited the best performance for ECH of LA, leading to 86.1 % of LA conversion, 99.7 % of selectivity towards valeric acid and 60.8 % of Faradaic efficiency at −1.5 V vs RHE. The excellent performance is mainly attributed to the modification of the electronic structures by the ligand and strain effects. Meanwhile, the relatively high electrochemically active surface area and the low charge transfer resistance are also conducive to improving the catalytic performance.

Advances in Selective Electrocatalytic Hydrogenation of Alkynes to Alkenes.

Selective electrochemical hydrogenation of alkynes to alkenes under ambient conditions is a promising alternative to the traditional energy-intensive and high-cost thermocatalytic hydrogenation. However, the systematic summary on the electrocatalysts and electrolyzers remains lacked. Herein, we demonstrate a comprehensive review about recent achievements in the electrocatalysts including noble metal and non-noble-metal materials. Several effective strategies of catalyst design were developed to improve alkyne conversion, and alkene selectivity, for example, accelerating the formation of active hydrogen species, enhancing alkyne adsorption and suppressing the side reactions. Furthermore, the advantages and disadvantages of various electrolyzers are systematically discussed. Accordingly, major challenges and future trends in this field are proposed.

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

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

Selective electroreduction of levulinic acid by controlling the crystalline structure of PbO on electrodes

Electrocatalysis of biomass-derived platform molecules is an effective way to utilize biomass. Electrodes for the electrocatalytic hydrogenation of levulinic acid (LA) to selectively produce valeric acid (VA) have been extensively studied. Improving the electrocatalytic activity of electrodes for LA conversion is a meaningful and challenging task. This paper prepared β-PbO/Pb electrodes by laser processing. The higher adsorption of LA on the β-PbO surface was confirmed by in situ infrared and Raman spectra and density functional theory (DFT) calculations. The β-PbO/Pb electrode exhibited higher electrocatalytic activity than the α-PbO/Pb and Pb electrodes. Complete conversion of LA was achieved at a much lower electrode potential of −1.4 V (vs RHE) with an 85 % yield of VA and greater than 90 % selectivity. In addition, laser processing technology provides a strategy for the rapid processing of electrodes to enable large-scale continuous production in industry.

Diastereoselective Electrocatalytic Hydrogenation of Cyclic Ketones Using a Proton-Exchange Membrane Reactor: A Step toward the Electrification of Fine-Chemical Production

We report the diastereoselective electrocatalytic hydrogenation of cyclic ketones using a proton-exchange membrane (PEM) reactor. The adsorbed monatomic hydrogen species (Hads) generated from protons at the triple-phase boundary of the cathode were found to reduce cyclic ketones with high diastereoselectivity. As high as 94% cis-selectivity was realized under optimal conditions upon using a Rh catalyst. Operando infrared spectroscopy enabled the direct observation of the adsorbed ketone involved in the reaction. We also demonstrate 5 g scale electrolysis of 4-tert-butylcyclohexanone by coupling the hydrogenation process with water oxidation as an anodic reaction. This reaction successfully produced cis-4-tert-butylcyclohexanol, which is 52 times more expensive than the starting material, according to commercial prices, uses only electrical energy and water as the reagent, and, remarkably, does not require H2 gas. This study demonstrates the potential of PEM reactors as reliable, robust, and green systems for the electrochemical production of fine chemicals.

Electrochemical hydrogenation of oxidized contaminants for water purification without supporting electrolyte

Electrocatalytic hydrogenation enables the efficient treatment of oxidized contaminants in water under mild conditions, but its application has been greatly hindered by the need for a supporting electrolyte and the large amounts of unsafe intermediate products. Here we report the development of a rhodium nanoparticle-modified palladium membrane electrochemical reactor (Rh NPs-PdMER) for the hydrogenation of oxidized contaminants in drinking water and industrial effluents. The Rh NPs-PdMER not only enabled the hydrogenation of 12 different oxidized contaminants to safe products with ≥99% conversion and ≥95% yield in water without a supporting electrolyte, but also required a very low operating voltage of only 1.4 V. The performance of the Rh NPs-PdMER can be attributed to the specific reactor configuration and the unique adsorbability of the hydrogenated intermediates of the oxidized contaminants to the Rh nanoparticles.

Electrocatalytic hydrogenation of indigo by NiMoS: energy saving and conversion improving.

An NiMo alloy bonded with sulfur (NiMoS) exhibits enhanced surface affinity toward water and organic molecules, thereby enhancing electrocatalytic hydrogenation (ECH) reactions through synergistic effects. In industrial processes, indigo, an ancient dye employed in the denim industry, is typically chemically reduced using sodium dithionite. However, this process generates an excess of toxic sulfide, which heavily contaminates the environment. ECH is a sustainable alternative for indigo reduction due to its reduced reliance on chemicals and energy consumption. In this study, carbon-felt (CF)-supported NiMoS was synthesized in a two-step process. First, the NiMo alloy was electrodeposited onto the CF surface, followed by sulfidation in an oven at 600 °C. NiMoS exhibits a larger electrochemically active surface area and a smaller charge transfer resistance compared to pure Ni and NiMo. Furthermore, NiMoS demonstrates excellent thermodynamic and kinetic properties for water splitting in strong alkaline solutions (1.0 M KOH). Additionally, optimal reaction conditions for the ECH of indigo were explored. Under the conditions of a 1.0 M KOH hydroxide medium with 10% methanol (v/v), an indigo concentration of 5 g L-1, a reaction temperature of 70 °C, and a current density of 10 mA cm-2, NiMoS/CF achieved remarkable improvements in both conversion (99.2%) and Faraday efficiency (38.1%). The results of this experimental work offer valuable insights into the design and application of novel catalytic materials for the ECH of vat dyes, opening up new possibilities for sustainable and environmentally friendly processes in the dye industry.

Unraveling the reaction mechanisms for furfural electroreduction on copper.

Electrochemical routes for the valorization of biomass-derived feedstock molecules offer sustainable pathways to produce chemicals and fuels. However, the underlying reaction mechanisms for their electrochemical conversion remain elusive. In particular, the exact role of proton-electron coupled transfer and electrocatalytic hydrogenation in the reaction mechanisms for biomass electroreduction are disputed. In this work, we study the reaction mechanism underlying the electroreduction of furfural, an important biomass-derived platform chemical, combining grand-canonical (constant-potential) density functional theory-based microkinetic simulations and pH dependent experiments on Cu under acidic conditions. Our simulations indicate the second PCET step in the reaction pathway to be the rate- and selectivity-determining step for the production of the two main products of furfural electroreduction on Cu, i.e., furfuryl alcohol and 2-methyl furan, at moderate overpotentials. We further identify the source of Cu's ability to produce both products with comparable activity in their nearly equal activation energies. Furthermore, our microkinetic simulations suggest that surface hydrogenation steps play a minor role in determining the overall activity of furfural electroreduction compared to PCET steps due to the low steady-state hydrogen coverage predicted under reaction conditions, the high activation barriers for surface hydrogenation and the observed pH dependence of the reaction. As a theoretical guideline, low pH (<1.5) and moderate potential (ca. -0.5 V vs. SHE) conditions are suggested for selective 2-MF production.

Efficient furfural hydrogenation to furfuryl alcohol using a PtCo bimetallic catalyst in a fluidized electrocatalysis system

Electrocatalytic hydrogenation (ECH) proved to be a highly efficient and eco-friendly approach for transforming biomass derivatives into valuable chemicals and biofuels, although in most cases, the reaction time was lengthy.

Comparative life cycle assessment of corn stover conversion by decentralized biomass pyrolysis-electrocatalytic hydrogenation versus ethanol fermentation

Biomass fast pyrolysis followed by electrocatalytic hydrogenation (Py-ECH) with renewable electricity outperforms cellulosic ethanol in three environmental impact categories.

Alloying promotion of Pd-based metallenes in electrocatalytic hydrogenation of functionalized nitroarenes

Pd–M (M = Cr, Mo, and W) metallenes are for the first time introduced as efficient electrocatalysts for the ECH of nitroarenes, in which the alloying promotion can be intrinsically ascribed to the boosted chemisorption/activation of a nitro group.

Electrocatalysis as an efficient alternative to thermal catalysis over PtRu bimetallic catalysts for hydrogenation of benzoic acid derivatives

PtRu bimetallic nanoclusters electrodeposited on carbon paper catalysts show highly efficient and uniquely selective electrocatalytic hydrogenation of aromatic rings in benzoic acid derivatives under mild and environmentally-friendly conditions.

Coral-shaped PtRu/Ni(OH)2 electrocatalyst promotes selective hydrogenation of benzoic acid

A novel PtRu/Ni(OH)2 electrode with a unique coral-shaped architecture was developed for electrocatalytic hydrogenation of benzoic acid into cyclohexanecarboxylic acid, simultaneously showing record conversion, selectivity and faradaic efficiency.