Electrocatalytic Oxidation Of Alcohols Research Articles

Anode Catalysts for Electrocatalytic Alcohol Oxidation Coupled to CO2 Reduction in Continuous-Flow Electrolyzers

Thanks to the intense scientific interest, the field of CO2 electrolysis witnessed remarkable progress (industrially relevant partial current densities, selective electrocatalysts towards small molecule products, multi-cell stacks, etc.) in the past decade. However, despite all these efforts, the energy efficiency of CO2 electrolyzers is still relatively low, which is rooted in the large cell voltages. A reason behind this is that the kinetically sluggish water oxidation (OER) is performed at the anode in parallel with CO2 reduction (CO2RR) at the cathode. This issue can be circumvented by coupling CO2RR with alternative anode processes, resulting in smaller cell voltage (better energy efficiency) along with the possible generation of products at the anode with high market value. Thus, maximizing the potential of utilizing waste carbon sources to generate value-added products. Such alternative reactions include, for example, the electrocatalytic oxidation of chloride ions, aliphatic and aromatic alcohols, amines, urea, hydrazine, and numerous biomass-derived substances such as 5-(hydroxymethyl)furfural, sorbitol, etc.In this study, CO2RR to CO was driven at the cathode, and the electrocatalytic oxidation of glycerol (GOR) was performed at the anode of a small (1 cm2 active surface area) microfluidic electrolyzer cell. Ir black was replaced by carbon-supported Pt nanoparticles, while Ag nanoparticles were used as the cathode catalyst. During our experiments, we identified four main factors influencing the GOR activity and selectivity: i) the quality and quantity of the used ionomer, ii) the electrolyte flow rate, iii) glycerol concentration, and iv) the applied anode potential. The latter was particularly important since Pt showed the highest activity toward GOR in a potential window where its surface starts to oxidize. The formation of a continuous oxide layer has to be avoided since it inhibits the alcohol oxidation reaction. By setting optimal conditions, a close to 100% Faradic efficiency (FE) toward CO formation on the cathode and between 70-80% FE toward GOR was achieved above 200 mA cm-2 total current density. The amount of the formed products were tracked by mass spectrometry, gas-, and high-performance liquid chromatography, and nuclear magnetic resonance spectroscopy. Dihydroxyacetone, glycerate, glycolate, oxalate, tartronate, formate, and lactate were identified as GOR products. The missing charge was attributed to the formation and a small amount of CO2. To improve the stability and selectivity of Pt in GOR, semipermeable metal oxide layers were introduced to the top of the catalyst layer. The thin films were synthesized by electrodeposition in different thicknesses. Based on our measurements, a set of criteria were defined regarding the composition of the anode catalyst layer (ionomer, co-catalyst overlayer, etc.), the composition of the electrolyte solution, and the applied electrochemical protocol to allow stable and selective GOR at high achievable current densities.

Graphene as a Platform in Surface-Enhanced Infrared Absorption Spectroscopy (SEIRAS) for Amino-TEMPO Electro-Grafting

2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) has emerged as an environmentally benign catalyst for the electrochemical oxidation of primary and secondary alcohols to aldehydes and ketones (1). This simple organic free radical reagent possesses high activity, and versatility, and is one of the most promising alternatives to noble metal catalysts that were previously studied. The catalytic activity and reactivity of TEMPO is mostly studied in bulk solutions, for fuel cells, aqueous redox flow batteries and sensors (2, 3). For more practicality, various approaches were developed to immobilize TEMPO on active supports, such as anionic polyelectrolytes, and the electropolymerization of TEMPO-substituted pyrrole or thiophene (4, 5). However, these substrates suffer from instability, loss of catalytic activity, degradation of the polymer film in alkaline environment mostly used for TEMPO regeneration. One other way, is to use carbon-based substrates that are stable in aqueous acid and base environment, as well as non-aqueous solutions and have shown enhanced electrocatalytic behavior (6, 7).In this work, we studied the electro-grafting of amino-TEMPO on graphene using in-situ attenuated total reflection infrared absorption spectroscopy (ATR-IRAS). We observed that TEMPO is attached on the surface through covalent bonding between the amine and the graphene lattice, as previously reported (6, 7). While grafting was successfully demonstrated via the oxidation of the primary amine to a radical cation which reacted with the graphene surface, ATR-surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS) provided additional spectral feature confirming TEMPO grafting through plasmon induced signal enhancement. Hickey, D. P.; Milton, R. D.; Chen, D.; Sigman, M. S.; Minteer, S. D., TEMPO-Modified Linear Poly(ethylenimine) for Immobilization-Enhanced Electrocatalytic Oxidation of Alcohols. ACS Catalysis 2015, 5 (9), 5519-5524. Mishra, A.; Kim, J.; Zorigt, M.; Romo, A. I. B.; Gaddam, R.; Braun, J. E.; Ziviani, D.; Rodríguez-López, J., Highly Selective TEMPO Catalyzed Bulk Electrooxidation of Isopropanol to Acetone for Application in Electrochemical Heat Pumping. ACS Sustainable Chemistry & Engineering 2023, 11 (16), 6241-6249. Elouarzaki, K.; Mandoc, L.-R. P.; Gorgy, K.; Holzinger, M.; Amarandei, C.-A.; Ungureanu, E.-M.; Cosnier, S., Synthesis and electrochemical characterization of original “TEMPO” functionalized multiwall carbon nanotube materials: Application to iron (II) detection. Electrochemistry Communications 2015, 60, 131-134. Belgsir, E. M.; Schäfer, H. J., Selective oxidation of carbohydrates on Nafion®–TEMPO-modified graphite felt electrodes. Electrochemistry Communications 2001, 3 (1), 32-35. Grimshaw, J.; Perera, S. D., Poly(pyrrole-pyromellitimide) modified electrodes. Journal of Electroanalytical Chemistry and Interfacial Electrochemistry 1990, 278 (1), 279-286. Barman, K.; Askarova, G.; Jia, R.; Hu, G.; Mirkin, M. V., Efficient Voltage-Driven Oxidation of Water and Alcohols by an Organic Molecular Catalyst Directly Attached to a Carbon Electrode. Journal of the American Chemical Society 2023, 145 (10), 5786-5794. Yuan, B.; Xu, C.; Zhang, D.; Zhang, R.; Su, H.; Guan, P.; Nie, J.; Fernandez, C., Electrografting of amino-TEMPO on graphene oxide and electrochemically reduced graphene oxide for electrocatalytic applications. Electrochemistry Communications 2017, 81, 18-23.

Enhanced electrocatalytic alcohol oxidation mediated with ultra-low concentration of aminoxyl radicals via an Intermediate-Rich local microenvironment

Indirect electrocatalytic alcohol oxidation mediated by aminoxyl radicals generally requires large amounts of aminoxyl radicals to activate the oxidation of alcohols, which limits its potential for industrial utilization. In this study, the cavity structure of carbonaceous nano-volcanoes (CNV) grown on 3D graphite felt as nanoreactors advantageously provides a microenvironment with high compartmentalised reactant concentrations for efficient electrocatalytic alcohol oxidation. By extending the retention time of reactant molecules in the CNV through cavity enrichment, their interaction probability with the electrodes was maximized, resulting in the intensification of mass transport and kinetically favorable settings. Meanwhile, abundant oxygen-containing functional groups on the surface constructed by the CNV provided hydrogen bonding forces to anchor the reactive aminoxyl radicals (4-acetamido-2,2,6,6-tetrame-thylpi-peridin-1-oxyl, ACT) during the reaction. Based on the intermediate-rich local microenvironment, a high turnover frequency of up to 31818 h−1 can be achieved even with only 0.5 mol% ACT-mediated. The electrocatalytic oxidation of benzyl and heterocyclic substrates can be achieved by this method under mild conditions. To showcase the synthetic efficacy and practical applicability of this approach, the successful oxidation of a chiral primary alcohol precursor to the generic drug levetiracetam was demonstrated on a larger scale, presenting further evidence of its practicality and usefulness in chemical synthesis.

Process intensification enhanced continuous flow for the effective coupling of sterol electrooxidation with H2 evolution using NiMo-based electrocatalysts

The electrocatalytic oxidation (ECO) of steroid alcohols at the anode is sustainable approach to synthesize valuable steroid carbonyls. This process is coupled with the hydrogen evolution reaction (HER) occurring at the cathode, further enhancing its environmental benefits. However, determining compatible electrocatalysts facilitating production of steroid carbonyls and hydrogen poses challenge. Hence, synergistically enhanced electrocatalytic approach was proposed, whereby NiMoO4 and the aminoxyl radical mediator 4-acetamido-TEMPO (ACT) were used together at the anode, in combination with Ni0.2Mo0.8N at the cathode. In situ experiments and theoretical calculations revealed that the introduction of Mo facilitates the formation of NiOOH and provides stabilization of ACTH (the reduced form of ACT) on the NiMoO4 surface. The effect of Mo also contributed to avoid the H* over-binding to decrease the HER energy barrier. This study aims to establish systematic approach towards the rational design of electrocatalysts that can be used to produce value-added steroid carbonyls and H2.

Modification Strategies for Development of 2D Material-Based Electrocatalysts for Alcohol Oxidation Reaction.

2D materials, such as graphene, MXenes (metal carbides and nitrides), graphdiyne (GDY), layered double hydroxides, and black phosphorus, are widely used as electrocatalyst supports for alcohol oxidation reactions (AORs) owing to their large surface area and unique 2D charge transport channels. Furthermore, the development of highly efficient electrocatalysts for AORs via tuning the structure of 2D support materials has recently become a hot area. This article provides a critical review on modification strategies to develop 2D material-based electrocatalysts for AOR. First, the principles and influencing factors of electrocatalytic oxidation of alcohols (such as methanol and ethanol) are introduced. Second, surface molecular functionalization, heteroatom doping, and composite hybridization are deeply discussed as the modification strategies to improve 2D material catalyst supports for AORs. Finally, the challenges and perspectives of 2D material-based electrocatalysts for AORs are outlined. This review will promote further efforts in the development of electrocatalysts for AORs.

Selective electrocatalytic conversion of primary alcohols to nitriles on nickel-cobalt nitride/oxide tandem electrocatalyst

Nitriles are vital precursors in the production of pharmaceuticals, advanced materials and many other commercial chemicals. Conventional approaches for nitrile synthesis are limited by the utilization of highly toxic cyanide ion and harsh conditions. The electrochemical conversion of primary alcohols and ammonia to nitriles offers a cost-effective and green approach to prepare nitriles, which requires highly efficient and selective catalysts to drive the cascade reaction and minimize side reactions. Here, we demonstrate how nitriles can be selectively synthesized by electrocatalytic oxidation of benzyl alcohol and ammonia on NiCo nitride and oxide that are co-localized on carbon cloth (NiCo-N,O/CC) electrode. In this electrocatalyst, the oxidation from alcohols to aldehydes is mainly catalyzed by NiCo oxide, while the oxidation from imine to nitrile is mainly catalyzed by NiCo nitride, endorsing preferential oxidation and cascade reactions on these catalytic interfaces. A total faradaic efficiency of 52%, productivity rate of 35 μmol cm-2h−1 and 70.1% selectivity of nitriles was achieved at 1.53 V vs RHE. The two interface NiCo-N,O/CC tandem electrocatalyst revealed synergistic activity and selectivity superior to NiCo-O/CC with single interface. Our results demonstrate that the utilization of tandem catalytic mechanisms could create new prospects in designing electrocatalysts for cascade reactions.

Fe Electron Center Local Regulation of CoFe‐Layered Double Hydroxides Nanosheets for Enhancing the Electrocatalytic Oxidation of Benzyl Alcohol

AbstractReplacing sluggish oxygen evolution reaction (OER) with electrocatalytic oxidation (ECO) of alcohols was a promising hotspot due to its advantages of requiring low potential, inhibiting mixing of gases, and forming value‐added products. In the ECO of alcohols process, Fe electron centers of Fe‐based layered double hydroxides (LDHs) can regulate the d band of LDHs overlap, optimize the active local structure of LDHs, and then enhance the electrocatalytic oxidation performance. In this work, CoxFey‐LDHs nanosheets with different ratios of Co/Fe were prepared for selective ECO of benzyl alcohol (BA) to benzoic acid (BAC). Comprehensive characterizations revealed that the adjustment of bandgap and OH species adsorption of CoxFey‐LDHs resulted in the appropriate thermodynamic driving force, which improved the electrical conductivity of CoxFey‐LDHs and enhanced their ECO of BA. Especially, the as‐prepared Co3Fe1‐LDH showed intriguing electrocatalytic activity and only required a potential of 1.51 V (vs. RHE) to achieve a total current density of 50 mA cm−2 in alkaline solution containing 10 mM BA with a conversion (96.79 %) of BA and selectivity (94.93 %) of BAC, which was 60 mV lower than that of OER. After six cycles, Co3Fe1‐LDH still achieved 94.74 % conversion of BA and 92.10 % selectivity of BAC without significant degradation.

Enhanced electrocatalytic glycerol oxidation on CuCoN0.6/CP at significantly reduced potentials

Electrocatalytic alcohol oxidation coupled with the hydrogen evolution reaction, wherein a thermodynamically favorable oxidation reaction replaces the sluggish kinetics of the oxygen evolution reaction, has recently attracted considerable attention. However, the development of nonprecious-metal electrocatalysts capable of delivering much lower oxidation potentials holds great significance. In this study, we proposed and developed CuCoN0.6 nanowires loaded on conductive carbon paper (denoted as CuCoN0.6/CP) as an efficient catalyst for selective glycerol oxidation to formate. Our catalyst achieved a remarkably high faradic efficiency of 90.0% towards formate production. More notably, it required an anode potential as low as 1.07 V to achieve a current density of 10 mA cm−2, a significantly lower potential than that reported in the literature. Experimental characterizations reveal that the oxidations of Cu+ and Co2+ ions promoted the formation of reactive hydroxyl species, which are responsible for the substantially reduced oxidation potential and enhanced glycerol oxidation performance. Furthermore, we investigated the reaction pathway of glycerol oxidation and structural changes in the catalysts. The catalyst reconstruction led to the formation of CoOOH, which is considered as the active site for glycerol oxidation. Finally, we successfully separated high-purity and value-added potassium diformate product. This work not only advances the electrocatalytic conversion of biomass-derived alcohols but also provides insights into the design of electrocatalysts with broad applications.

Selective electrooxidation of 2-hydroxybenzyl alcohol coupled with H2 production promoted by surface reconstruction of β-Ni(OH)2 nanosheets

2-Hydroxybenzaldehyde (SALD) exhibits special reactivity in various chemical reactions due to the existence of aldehyde and hydroxyl groups, which also make it a challenge to achieve high conversion and selectivity for SALD production. Herein, β-Ni(OH)2 nanosheets over nickel foam (NF) at different hydrothermal temperatures were synthesized for electrocatalytic oxidation (ECO) of 2-hydroxybenzyl alcohol (SAL) into SALD. The β-Ni(OH)2 electrode obtained at 160 °C achieves the best ECO performance in 2.5 M KOH at the applied potential of 1.45 V (RHE), showing the SALD selectivity of 78.90% and the Faradaic efficiency of 87.94% at the SAL conversion of 69.76%. ECO of SAL reduces the cell voltage and boosts the hydrogen productivity by 2.74 times. It is of great importance to find that potential-driven surface reconstruction of β-Ni(OH)2 enables selective conversion of SAL into SALD. Side reactions including OER as well as oxidation of phenolic group can be effectively controlled via regulating applied potentials on β-Ni(OH)2. This work is the first report on direct electrochemical oxidation of SAL with high SALD selectivity, and offers a green and clean strategy for highly selective production of SALD under mild conditions.

Oxidant-Free Electrochemical Direct Oxidative Benzyl Alcohols to Benzyl Aldehydes Using Three-Dimensional Printing PPAR Polyoxometalate.

The oxidation of benzyl alcohols is an important reaction in organic synthesis. Traditional methods for benzyl alcohol oxidation have not been widely utilized due to the use of significant amounts of precious metals and environmentally unfriendly reagents. In recent years, electrocatalytic oxidation has gained significant attention, particularly electrochemical anodic oxidation, which offers a sustainable alternative for oxidation without the need for external oxidants or reducing agents. Here, a copper monosubstituted phosphotungstate-based polyacrylate resins (Cu-LPOMs@PPAR) catalyst has been fabricated with immobilization and recyclability using 3D printing technology that can be successfully applied in the electrocatalytic oxidation of benzyl alcohol to benzaldehyde, achieving atom economy and reducing pollution. In this protocol, we obtain benzaldehyde in good yields with excellent functional group toleration under metal-free and oxidant-free conditions. This strategy could provide a new avenue for heterogeneous catalysts in application for enhancing the efficiency and selectivity of electrocatalytic oxidation processes.

Pyrolysis of ZIF-8 to PdZn alloy nanoparticles on carbon doping with nitrogen for highly efficient electrocatalytic alcohol oxidation

MOFs (metal-organic frameworks) materials have been widely applied in sensing and catalysis, with the advantages of large surface area, numerous active sites, controllable size and morphology. Herein, we report the preparation of the caged PdZn/NC catalysts with the PdZn alloy nanoparticles on carbon doping with nitrogen owing high electrocatalytic performance by using a hydrothermal synthesis and pyrolysis strategy. The caged structure and PdZn alloy are demonstrated by a series of advanced characterization techniques. The material combines the advantages of bimetallic alloy and MOFs cage structure to realize highly efficient electrocatalytic oxidation of ethanol oxidation reactions (EOR) and methanol oxidation reactions (MOR) simultaneously. Electrochemical test results show that PdZn/NC-2 has a mass activity of 2.41 A mg−1pd and 2.64 A mg−1pd for methanol and ethanol oxidation, respectively, which is 12.68 times (MOR) and 14.67 times (EOR) higher than that of commercial Pd/C. This is probably attributed to the cage-like structure of PdZn/NC separating the Pd nanoclusters, resulting in high Pd dispersion. Simultaneously, the electronic property of Pd is adjusted after the formation of the complete PdZn alloy, improving the desorption of the carbon-based intermediates from the Pd active sites. This increases the CO poisoning resistance, resulting in good alcohol electrocatalytic oxidation activity and stability.

Nitroxide radical surfactants enable electrocatalytic oxidation of fatty alcohols in water

TEMPO-functionalized surfactants are developed for the electrocatalytic oxidation of fatty alcohols to corresponding carbonyl compounds in water with up to 93% total conversion.

In situ construction of NiCo2O4 nanosheets on nickel foam for efficient electrocatalytic oxidation of benzyl alcohol

A NiCo2O4/NF catalyst with a nanosheet structure was designed, and it exhibited excellent catalytic activity and stability for the ECO of benzyl alcohol.

A high-index facet gold 12 tip nanostar for an improved electrocatalytic alcohol oxidation reaction with superior CO tolerance.

Direct alcohol fuel cells have a long and promising future, which will require the development of highly active electrocatalysts for alcohol electrooxidation reactions. To this end, high-index facet nanomaterial-based electrocatalysts provide significant promise for the successful oxidation of alcohols. However, the fabrication and exploration of high-index facet nanomaterials are seldom reported, especially in electrocatalytic applications. Herein, we successfully synthesized a high index facet {711} Au 12 tip nanostructure for the first time using a single-chain cationic TDPB surfactant. Electrooxidation results demonstrate that a {711} high-index facet Au 12 tip exhibited much higher electrocatalytic activity (∼10-fold higher) than the {111} low-index facet Au nanoparticles (Au NPs) without being poisoned by CO under identical conditions. Besides, Au 12 tip nanostructures offer appreciable stability and durability. The high electrocatalytic activity with excellent CO tolerance is due to the spontaneous adsorption of the negatively charged -OH on the high-index facet Au 12 tip nanostars, as evidenced by the isothermal titration calorimetry (ITC) analysis. Our findings suggest that high-index facet Au nanomaterials are ideal candidate electrode materials for the electrooxidation reaction of ethanol in fuel cells.

Merging electrocatalytic alcohol oxidation with C-N bond formation by electrifying metal-ligand cooperative catalysts.

Electrification of thermal chemical processes could play an important role in creating a more energy efficient chemical sector. Here we demonstrate that a range of MLC catalysts can be successfully electrified and used for imine formation from alcohol precursors, thus demonstrating the first example of molecular electrocatalytic C-N bond formation.This novel concept allowed energy efficiency to be increased by an order of magnitude compared to thermal catalysis. Molecular EAO and the electrification of homogeneous catalysts can thus contribute to current efforts for the electrocatalytic generation of C-N bonds from simple building blocks.

Identification and Origination of the O*-Dominated β-NiOOH Intermediates with High Intrinsic Activity for Electrocatalytic Alcohol Oxidation

Identification and Origination of the O*-Dominated β-NiOOH Intermediates with High Intrinsic Activity for Electrocatalytic Alcohol Oxidation

Impedimetric study of the electrocatalytic oxidation of alcohols by nickel-Schiff base metallopolymer: Potential application for forensic identification of alcoholic beverage contaminants by multivariate data analysis

The present paper presents a systematic electrochemical impedance study on the electrooxidation of methanol, ethanol, 1-propanol, ethylene glycol and glycerol by a sensor based on nickel-salen metallopolymer. As a second step, the application simulated the device in the identification of contamination in alcoholic beverages by principal component analysis (PCA). By studying electrochemical impedance, we verified that the reactivity of alcohols on the device is directly related to pKa values and polarity index. By multivariate analysis, it was possible to set up a system that differentiates the types of alcohol with impedimetric variables. The identification distance between the groups allowed the differentiation of mixed samples from the groups containing ethanol-methanol and ethanol-ethylene glycol.

Salting‐Out Aldehyde from the Electrooxidation of Alcohols with 100 % Selectivity

AbstractSelective electrocatalytic oxidation of alcohols to value‐added aldehydes has attracted increasing attention. However, due to its higher reactivity than alcohol, the aldehyde is easily over‐oxidized to acid in alkaline electrolytes. Herein we realize the selective electrooxidation of alcohol to aldehyde on NiO by tuning the local microenvironment to salt out the aldehyde from the reaction system. The origin of the high selectivity was found to be the inhibition of the hydration of aldehydes, which is the result of the decreased alkalinity and the increased cation and substrate concentration. This strategy could salt out the aldehyde at the gas|electrolyte interface from the electrooxidation of alcohol with 100 % selectivity and be easily extended to other selective oxidation reactions, such as 5‐hydroxymethyl furfural (HMF) to 2,5‐furandicarboxaldehyde (DFF) and amine to an imine.

Salting-Out Aldehyde from the Electrooxidation of Alcohols with 100 % Selectivity.

Selective electrocatalytic oxidation of alcohols to value-added aldehydes has attracted increasing attention. However, due to its higher reactivity than alcohol, the aldehyde is easily over-oxidized to acid in alkaline electrolytes. Herein we realize the selective electrooxidation of alcohol to aldehyde on NiO by tuning the local microenvironment to salt out the aldehyde from the reaction system. The origin of the high selectivity was found to be the inhibition of the hydration of aldehydes, which is the result of the decreased alkalinity and the increased cation and substrate concentration. This strategy could salt out the aldehyde at the gas|electrolyte interface from the electrooxidation of alcohol with 100 % selectivity and be easily extended to other selective oxidation reactions, such as 5-hydroxymethyl furfural (HMF) to 2,5-furandicarboxaldehyde (DFF) and amine to an imine.

The Synergy of Tensile Strain and Ligand Effect in PtBi Nanorings for Boosting Electrocatalytic Alcohol Oxidation

AbstractAs the best electrocatalysts for alcohol oxidation reactions in direct alcohol fuel cells (DAFCs), Pt‐based nanomaterials still face the challenges of low utilization efficiency of Pt atoms and poor reaction kinetics. To address these issues, a self‐etching strategy is developed to prepare PtBi nanorings (NRs) with abundant low‐coordinated atoms and inhomogeneous tensile strain (≈4%). The obtained PtBi NRs exhibit superior activity toward methanol oxidation reaction (MOR) and ethanol oxidation reaction (EOR) in alkaline media. Particularly, the mass activities of PtBi NRs for MOR and EOR are 9.4 and 8.5 times higher than those of commercial Pt/C, respectively, which are among the best in the reported Pt‐based catalysts. The highly open structure of PtBi NRs is believed to provide plentiful catalytic active sites and increase the utilization of Pt atoms. Theoretical calculations show that the two important factors, i.e., adsorption energy with the key reaction intermediates and the energy barrier for the potential‐determining step, are significantly optimized owing to the synergy of tensile strain and the ligand effect in PtBi NRs. This study offers a promising strategy for the rational design and preparation of highly efficient catalysts for DAFCs.