Ethanol Oxidation Research Articles

In Situ X-ray and Infrared Spectroscopic Studies of Electrochemical Systems

Abstract Despite a wealth of data and intense research, the phenomena occurring during electrocatalysis are still a major obstacle in many chemical processes. Molecular analysis of the electrode/electrolyte interface is needed to correctly describe the reaction through identifying the species involved, their interaction with the environment and kinetics in situ, i.e. while the reaction is taking place. That can be done by coupling the electrochemical system with complementary non-electrochemical techniques. In addition, in situ x-ray spectroscopic techniques analyze the electrode itself, providing the information on the changes in the catalyst during the reaction. The synergy of the traditional electrochemical techniques with the complementary spectroscopic methodologies offer understanding of the electrode/electrolyte interface above and beyond traditional experimental mainframe. Here we demonstrate how in situ X-ray absorption spectroscopy, in situ infrared reflection/absorption spectroscopy, and traditional voltammetric studies can reveal electrochemical processes during oxidation of ethanol, enhance the structure and selectivity of the catalyst to complete oxidation pathway, and provide understanding of the parameters that enhance its oxidation for future designing catalysts for alcohol oxidation fuel cells.

A Nitrogen- and Carbon-Present Tin Dioxide-Supported Palladium Composite Catalyst (Pd/N-C-SnO2)

For the first time, nitrogen- and carbon-present tin dioxide-supported palladium composite catalysts (denoted as Pd/N-C-SnO2) were prepared via an HCH method (HCH is the abbreviation for the hydrothermal process–calcination–hydrothermal process preparation process). In this work, firstly, three catalyst carriers (denoted as cc) were prepared using a hydrothermal-process-aided calcination method, and catalyst carriers prepared using ammonia monohydrate (NH3∙H2O), N,N-dimethylformamide (C3H7NO) and triethanolamine (C6H15NO3) as the nitrogen sources were nominated as cc1, cc2 and cc3, respectively. Secondly, these catalyst carriers were reacted with palladium oxide monohydrate (PdO·H2O) hydrothermally to generate catalysts c1, c2 and c3. As testified by XRD and XPS, besides carbon materials and the N-containing substances, the main substances of all prepared catalysts were SnO2 and metallic palladium (Pd). Above all things, all resultant catalysts, especially c2, showed a prominent electrocatalytic activity towards the ethanol oxidation reaction (EOR). As indicated by the CV (cyclic voltammetry) results, all fabricated catalysts presented a clear electrocatalytic activity towards the EOR. In the CA (chronoamperometry) measurement, the faradaic current density of EOR measured on c2 at −0.27 V vs. an SCE (saturated calomel electrode) after 7200 s was still maintained at about 5.6 mA cm−2. Preparing a novel catalyst carrier, N-C-SnO2, and preparing a new EOR catalyst, Pd/N-C-SnO2, were the principal dedications of this preliminary work, which was very beneficial to the development of Pd-based EOR catalysts.

Enhancing Electrocatalytic Oxidation of Ethanol by PtAu Nanoalloy Supported on SnO2/GN in Acidic Medium

Enhancing Electrocatalytic Oxidation of Ethanol by PtAu Nanoalloy Supported on SnO₂/GN in Acidic Medium

Platinum and CeO2−x Occlusion Electrodeposition at Unsupported Vulcan XC-72R for Methanol and Ethanol Oxidation Reactions in Alkaline Media

Platinum was electrodeposited in a slurry solution of CeO2 and Vulcan XC-72R to produce Pt/CeO2−x/Vulcan XC-72R catalysts by using the Rotating Disk Slurry Electrodeposition (RoDSE) Technique. The activity of the catalysts was measured towards methanol and ethanol oxidation reactions in alkaline conditions by cyclic voltammetry and chronoamperometry. The electrochemical results were compared to those obtained on commercial catalysts. Pt/CeO2−x/Vulcan XC-72R (with ∼ 26 wt% Pt) catalyst was the most active for both alcohol oxidation reactions when compared to commercial 40 wt.% and 20% /Vulcan XC-72R (ETEK) catalysts. The mass activity increases 2.0x and 2.4x for methanol and ethanol oxidation reactions when compare with 40 and 20 Pt wt. % commercial catalysts, respectively. The Pt/CeO2−x/Vulcan XC-72R catalysts contained Pt nanoparticles growth within the cerium oxide through an occlusion electrodeposition method. These effects were systematically investigated using X-ray Diffraction (XRD), High Resolution Transmission Electron Microscopy (HR-TEM), and X-ray Photoelectron Spectroscopy (XPS).

Molybdenum-doping to enhance the deprotonation ability of nickel-based hydroxide electrocatalysts for ethanol oxidation

With technological advancements, the practical application of ethanol oxidation reaction (EOR) is becoming increasingly promising, yet the need for higher ethanol concentrations highlights the growing importance of the deprotonation ability (Ni2+ to Ni3+) of the catalyst. The deprotonation ability is the key step for nickel-based catalysts in EOR, as it is essential for Ni2+ to continuously undergo deprotonation to transform into Ni3+ in order to maintain the continuous EOR. Herein, we developed Mo-doped Ni(OH)2 nanosheets by a hydrothermal method. The Mo-doped Ni(OH)2 nanosheets show excellent EOR performance due to the high valence doping of Mo, the onset potential of the oxidation peak (Ni2+ to Ni3+) appears at a position with a small overpotential,. The in-situ Raman spectroscopy technique further characterized the increase in NiOOH in the process of EOR. The Mo-doped Ni(OH)2 nanocomposite catalyst facilitates the oxidation of Ni2+ into Ni3+. Based on the above theoretical guidance, Mo-doped Fe/Ni(OH)2 nanosheets was designed and synthesized. The outstanding EOR performance of the Mo-Fe/Ni(OH)2-3 showed a potential of 1.352 V at 10 mA cm−2. The catalyst was used to design three-electrode reversible zinc-ethanol-air battery (T-RZEAB), which effectively overcomes the opposing kinetic and thermodynamic requirements for EOR and oxygen reduction reaction (ORR) catalysts in the oxygen electrode. The charging voltage of T-RZEAB with Mo-Fe/Ni(OH)2-3 is 240 mV lower than that of a traditional zinc-air battery at 25 mA cm−2.

Flexible Ag@Au core–shell nanowires electrode fabrication with controllable nanogold size and thickness on silver nanowires/PDMS substrate toward enhanced ethanol electrooxidation

The synthesis of gold nanowires (AuNWs) is challenging due to difficulties in obtaining AuNWs of variable diameters and lengths. In this study, an effective approach to fabricating AuNWs with controllable lengths and diameters was developed on a flexible silver nanowires (AgNWs)/polydimethylsiloxane (PDMS) substrate. Gold nanoparticles were uniformly electrodeposited onto the flexible AgNWs/PDMS to form bimetallic Ag@Au core–shell NWs/PDMS. The results showed that the diameters and the lengths of the Ag@Au NWs were easily fine-tuned. The flexible Ag@Au NWs/PDMS electrode exhibited excellent mechanical, electrical, and electrochemical properties. In ethanol oxidation reaction (EOR), the Ag@Au NWs/PDMS achieved a peak current density of 28541.55 μA cm−2 (10 times higher than that of a commercial Au electrode) and 63.39% retaining activity in a stability test by chronoamperometry (over 2 times stable than values in literature). Finally, EOR and chromium (VI) determination by the Ag@Au NWs/PDMS in flexible integrated electrodes were performed to showcase the versatile feasibilities of this new material.

Additive-free Electrodeposition of SnCoNi Trimetallic Catalysts for Ethanol Electrooxidation

SnCoNi catalysts were synthesized via electrodeposition, with and without citric acid, to assess their ethanol electrooxidation performance. The additive-free catalyst exhibited superior properties, including lower charge transfer resistance and a smaller Tafel slope compared to the citric acid-modified catalyst. Chronoamperometry testing further revealed better electrochemical stability for the additive-free catalyst, with less current loss over time. Cyclic voltammetry confirmed the enhanced ethanol oxidation activity with a relatively high current density. The improved performance is attributed to better mass transport, active site exposure, and the synergistic effects of Sn, Co, and Ni in the additive-free catalyst, making it more efficient for ethanol electrooxidation. These findings suggest that the additive-free catalyst exhibits more favorable properties for ethanol electrooxidation compared to its citric acid-modified counterpart.

The Effect of Saccharin on SnNi Alloy: the Electrodeposition and its Electrocatalytic Activity in Ethanol Oxidation Reaction

The development of Direct Ethanol Fuel Cell (DEFC) has attracted much attention, as alternative energy sources due to its various advantages. However, among its various advantages, DEFC has several problems, such as the kinetics of the ethanol oxidation reaction. Transition metal-based catalysts such as nickel and tin are considered as potential catalysts for DEFC due to their oxophilic properties that can improve catalytic activity. In this study, the effect of saccharin on SnNi bimetallic alloy catalyst synthesized by electrodeposition method on copper wire substrate was investigated. SnNi samples were characterized by several techniques, including X-ray diffraction, Scanning electron microscopy, and energi dispersive X-ray spectrocopy. Saccharin addition had a significant effect on the morphology, crystallite size, and composition of the catalyst. The presence of saccharin causes the formation of more uniform particles and has a smaller size. The sample with the addition of saccharin had a smaller charge transfer resistance value 4.82 Ω, lower tafel slope by 115 mV/dec, and show higher jf/jb ratio by 0.55. Furthermore, as the current density decreases, the SnNi catalyst with saccharin has a slow decrease rate and higher stability than the SnNi catalyst without saccharin.

Synthesis of 1,1-diethoxyethane from ethanol using electrogenerated acid

Abstract We introduce a novel reaction where electrogenerated acid enhances ethanol upgrading. Electrochemical oxidation of ethanol produces acetaldehyde and protons; the protons act as electrogenerated acid, catalyzing acetalization to form 1,1-diethoxyethane. Stirring the solution shifts the reaction toward acetaldehyde production because electrogenerated acid is neutralized by an electrogenerated base at the cathode.

Facile Synthesis of Rhodium-Based Nanocrystals in a Metastable Phase and Evaluation of Their Thermal and Catalytic Properties.

Controlling the polymorphism of metal nanocrystals is a promising strategy for enhancing properties and discovering new phenomena. However, previous studies on Rh nanocrystals have focused on their thermodynamically stable face-centered-cubic (fcc) phase. Herein, a facile synthesis of Rh-based nanocrystals featuring the metastable hexagonal close-packed (hcp) phase is reported by using Ru seeds in their native hcp phase to template the deposition of Rh atoms. The success of such phase-controlled synthesis relies on the templating effect promoted by the small lattice mismatch between Ru and Rh and the slow dropwise titration of the precursor at an elevated temperature, ensuring the layer-by-layer growth mode and thus the formation of a conformal hcp-Rh shell. Faster injection rate of Rh(III) precursor leads to the formation of a rough Rh shell in the conventional fcc phase due to accelerated reaction kinetics. Considering both thermodynamic and kinetic aspects of this system, the hcp-Rh phase is favored when the low surface energy from smooth overlayers balances the high bulk energy of the metastable phase, achieved through tight control of reaction rates and deposition patterns. These Ruhcp@Rhhcp core-shell nanocrystals demonstrate thermal stability up to 400°C, while exhibiting higher catalytic activity toward ethanol oxidation reaction compared to Ruhcp@Rhfcc counterparts.

OH Regulator of Amorphous CrOx on Defect-Rich Ultrafine Pd Nanowires Boosts Electrocatalytic Ethanol Oxidation.

Reasonable construction of high activity and selectivity electrocatalysts is crucial to achieve efficient ethanol oxidation reaction (EOR). However, the oxidation of ethanol tends to produce CO species that poison the active centers of the EOR electrocatalysts. Herein, a unique amorphous CrOx-protected defect-rich ultrafine Pd nanowires (CrOx-Pd NWs) is developed. On the one hand, the CrOx layer can act as a protective layer to maintain the structure of the nanowire. On the other hand, it can play the role of OH regulator to optimize the adsorption energy barrier of intermediate species in Pd nanowire, thereby enhancing the ability of the catalyst to resist CO poisoning. The CrOx-Pd NWs exhibit excellent EOR performance with 3.64 times higher mass activity and 50mV lower CO electro-oxidation potential than commercial Pd black. The results show that the CrOx layer promotes the dissociation of H2O into OHads, while the CrOx transfers electrons to neighboring Pd atoms optimizing the electronic configuration of Pd, thus selectively oxidizing ethanol to acetate and preventing the formation of toxic *CO. This work provides an effective strategy for the synthesis of nanowire materials with oxide/metal interfaces and offers new ideas for the design of catalysts that can efficiently drive EOR.

Kinetic Understanding of Metal Ions Doping in Enhancing the Electrocatalytic Ethanol Oxidation Performance of Nickel Hydroxides

Kinetic Understanding of Metal Ions Doping in Enhancing the Electrocatalytic Ethanol Oxidation Performance of Nickel Hydroxides

Empowering Tri-Functional Palladium's Catalytic Activity and Durability in Electrocatalytic Formic Acid Oxidation Reaction via Innovative Self-Caging and Alloying Strategies.

Direct formic acid fuel cells (DFAFCs) stand out for portable electronic devices owing to their ease of handling, abundant fuel availability, and high theoretical open circuit potential. However, the practical application of DFAFCs is hindered by the unsatisfactory performance of electrocatalysts for the sluggish anodic formic acid oxidation reaction (FAOR). Palladium (Pd) based nanomaterials have shown promise for FAOR due to their highly selective reaction mechanism, but maintaining high electrocatalytic durability remains challenging. In this study, a novel Pd-based electrocatalyst (UiO-Pd-E) is reported with exceptional durability and activity for FAOR, which can be attributed to the Pd nanoparticles encapsulated within a carbon framework where concurrent chemical alloying of Pd and Zr occurs. Further, the UiO-Pd-E demonstrates noteworthy multifunctionality in various electrochemical reactions including electrocatalytic ethanol oxidation reaction (EOR) and oxygen reduction reaction (ORR) in addition to the FAOR, highlighting its practical potentials.

Sub-10 nm PdNi@PtNi Core–Shell Nanoalloys for Efficient Ethanol Electro-Oxidation

By controlling the structure and composition of Pt-based nanoalloys, the ethanol oxidation reaction (EOR) performances of Pt alloy catalysts can be effectively improved. Herein, we successfully synthesis sub-10 nm PdNi@PtNi nanoparticles (PdNi@PtNi NPs) with a core–shell structure by a one-pot method. The sub 10 nm core–shell nanoparticles possess more effective atoms and exhibit a synergistic effect which can lead to a shift in the d-band center and alter binding energies toward adsorbates. Due to the synergistic effect and unique core–shell structure, the PdNi@PtNi NP catalysts exhibit excellent electrocatalytic performance for ethanol oxidation reactions in alkaline, achieving 9.30 times more mass activity and 7.05 times more specific activity that of the state-of-the-art Pt/C catalysts. Moreover, the stability of PdNi@PtNi NPs was also greatly improved over PtNi nanoparticles, PtPd nanoparticles, and commercial Pt/C. This strategy provides a new idea for improving the electrocatalytic performance of Pt-based catalysts for EORs.

Construction of Multiphase Concave Tetrahedral PdInMo Nanocatalyst for Enhanced Alcohol Oxidation

AbstractHeterogeneous palladium‐based catalysts show excellent catalytic properties for electrocatalytic oxidation of alcohols, but the construction of such heterogeneous catalysts is a challenge. Here, a multiphase tetrahedral PdInMo nanocatalyst is prepared by a one‐pot reaction method. And the multiphase tetrahedral PdInMo nanocatalyst consists of a face‐centered cubic structure and an intermetallic structure. Due to the oxygen affinity of indium and molybdenum atoms, the interface defects of internal multiphase structure, and intermetallic structure, the multiphase concave tetrahedral PdInMo nanocatalyst shows enhanced catalytic efficiency in the electrocatalytic oxidation reaction of methanol and ethanol. Compared with commercial Pd/C catalysts, PdIn0.117Mo0.037 nanocatalyst has the best mass activity and specific activity. In electrocatalysis of methanol oxidation, the mass activity (2205.57 mA mgPd−1) and specific activity (6.67 mA cm−2) are 4.81 and 3.40 times than that of a commercial Pd/C nanocatalyst (458.5 mA mgPd−1, 1.96 mA cm−2), respectively. In the electrocatalysis of ethanol oxidation, the mass activity (2668.49 mA mgPd−1) and specific activity (8.11 mA cm−2) are 4.06 and 3.14 times than that of the commercial Pd/C nanocatalyst (655.83 mA mgPd−1, 2.58 mA cm−2), respectively. This study provides a reference for the design of highly efficient palladium catalysts for alcohol oxidation.

Liquid Metal Electrocatalyst with Ultralow Pt Loading for Ethanol Oxidation

Developing efficient and durable electrocatalysts for ethanol electro‐oxidation is crucial for enabling the application of direct ethanol fuel cell technology. Herein, it is demonstrated that Pt–Ga liquid metal‐based nanodroplets can serve as an efficient electrocatalyst to drive ethanol oxidation. The mass activity of Pt is significantly improved by alloying with liquid gallium. Guided by machine learning neural networks, a low‐concentration alkaline electrolyte is specifically formulated to allow electrodes with ultralow Pt loading to demonstrate remarkable activity toward ethanol oxidation with a mass activity as high as 13.47 A mg−1Pt, which is more than 14 times higher than that of commercial Pt/C electrocatalysts (i.e., 0.76 A mg−1Pt). Computational studies reveal that the superior activity is associated with the presence of Ga oxides adjacent to Pt on the catalyst surface which leads to energetically favorable pathways for the oxidation process. The findings reveal untapped opportunities in the realm of liquid metal catalysis and hold great promise for the future development of high‐performance alcohol fuel cells.

PtCu-a-SnO2 interface engineering on PtCu-SnO2 aerogels for ethanol oxidation electrocatalysis

Designing catalysts with high activity and stability to boost their ethanol oxidation reaction (EOR) performance is one of the central targets in the development of direct ethanol fuel cells (DEFCs). However, how to design the EOR catalysts in a rational way is still challenging, needing more efforts put in. Herein, we have synthesized a catalyst of PtCu-SnO2 aerogel via ingeniously introducing Cu into Pt-SnO2 system, resulting in the formation of a main phase of alloy (PtCu)-amorphous oxide (a-SnO2) interface. Benefiting from the optimized structures, the PtCu-SnO2 aerogel displays excellent acidic EOR performance with 4.5 times promotion in activity compared to pure Pt aerogel. In-depth investigations through electrochemical in-situ Fourier transform infrared spectroscopy and density functional theory calculations have shown that the absorbed OH on a-SnO2 surface together with the greatly-modified electronic structure of the alloy surface atoms can facilitate the C1 pathway and the oxidation of *CO intermediates for ethanol oxidation reaction. The resulting affinity of surface OH and the modification of reaction energies both in turn contribute to the improvement of EOR performance with high activity, stability, and anti-poisoning ability, proving interfacial engineering an effective strategy for the rational design of EOR catalyst.

Promoting role of Europium on Multi-Walled Carbon Nanotube (MWCNT) supported Platinum catalyst for Ethanol Electro-Oxidation in Direct Alcohol Fuel Cell (DAFC)

Implementing rare earth metals with platinum for Ethanol Oxidation Reactions (EOR) has received significant interest in the promising DEFC. Incorporation of europium, a rare earth metal, influences the electron density of the Pt, and the resulting catalytic activity is reinforced. Herein, different molar ratios of binary PtEu electrocatalysts supported over MWCNT were synthesized using the borohydride reduction method. The purpose of the investigation was to determine how the atomic structure, composition, and activity of the electrocatalyst correlate to the EOR. Structure, bulk composition, morphology, and bonding of the electrocatalyst were investigated through X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), Energy-Dispersive X-ray (EDX), Fourier Transform Infrared spectroscopy (FTIR), and RAMAN spectroscopy. Cyclic Voltammetry (CV), Linear Sweep Voltammetry (LSV), chronoamperometry (CA), and Electrochemical Impedance Spectroscopy (EIS) techniques were employed to probe the electro-oxidation kinetics on the electrocatalyst's surface. During the EOR circumstances, the PtEu electrocatalysts showed a captivating composition-structure-activity relationship, consistent with the findings. Notably, all the physical and electrochemical analyses demonstrate that the bimetallic composition of the 84:16 electrocatalyst has shown higher EOR activity through a bifunctional mechanism. The results provide novel insights into the ethanol oxidation process over bimetallic alloy electrocatalysts, which is crucial for designing robust and efficient electrocatalysts for DEFC.

Three-component NiO/Fe3O4/rGO nanostructure as an electrode material towards supercapacitor and alcohol electrooxidation

A nanocomposite made of nickel oxide and iron oxide (NiO/Fe3O4) and its hybrid with reduced graphene oxide (rGO) as a conductive substrate with a highly functional surface (NiO/Fe3O4/rGO) was synthesized using a simple hydrothermal approach. This study addresses the challenge of developing efficient materials for energy storage and alcohol fuel cells. After confirming the synthesis through structural analysis, the potential of these nanocomposites as supercapacitor electrodes and catalysts for methanol and ethanol oxidation in alcohol fuel cells were evaluated. The synergy of combining the two metal oxides and adding rGO to the composite structure led to excellent electrocatalytic activity in alcohol oxidation. For the modified NiO/Fe3O4/rGO electrode in the methanol oxidation reaction (MOR), a current density of 450 mA/cm2 at 0.67 V and excellent catalyst stability of 98.7% over 20 hours in chronoamperometric analysis were observed. In the ethanol oxidation reaction (EOR), an oxidative current of 235 mA/cm2 at a peak potential of 0.76 V was seen, with catalyst stability of 96.4% after 20 hours. As a supercapacitor electrode, the NiO/Fe3O4 composite demonstrated a specific capacitance of 946 F/g, while NiO/Fe3O4/rGO showed 1155 F/g. The stability of these electrodes after 10000 GCD cycles was 83.6% and 90.6%, respectively. These findings suggest that the proposed structures are cost-effective and reliable alternatives for energy storage and production, suitable for alcohol fuel cells and supercapacitors.

Stability of supported Pd-based ethanol oxidation reaction electrocatalysts in alkaline media

This study evaluates the dissolution of the supported electrocatalysts Pd/C, PdSn/C, PdNb/C, and PdFe3O4/C during ethanol oxidation reaction for Alkaline Direct Liquid Fuel Cells (ADLFC) applications. A scanning flow cell (SFC) combined to an inductively coupled plasma mass spectrometry (online ICP-MS) is used to assess the dissolution stability in a broad potential window. Accelerated stress tests with and without ethanol are developed using a rotating disk electrode (RDE) with dissolution products analysis by ex-situ ICP-MS. Potential profiles simulating those experienced by the catalyst during regular fuel cell operation were used. Sn and Fe catalysts demonstrate improved activity and stability compared with the material with Pd alone. For these reasons, PdSn/C and PdFe3O4/C are suitable for ADLFC applications. Severe Nb dissolution destabilizes Pd, increasing its leaching. This work demonstrates that while additional metals and oxides can improve the alcohol oxidation kinetics of Pd, these additives’ dissolution stability must already be considered at the catalyst design stage.