Onset Potential For Oxidation Research Articles

Sputtered Ag-doped NiO thin films: structural, optical, and electrocatalytic activity toward methanol oxidation

Significant research is being performed to find suitable electrocatalysts in alkaline direct methanol fuel cells. Despite tremendous improvements, producing non-Pt catalysts with great activity and high stability is still difficult. Herein, Ag-doped NiO thin films were deposited on fluorine-doped tin oxide (FTO) by the co-sputtering deposition method, utilizing various deposition times (200, 400, 600, and 800) seconds. The film thickness for the deposited films varied from 17, 35, 70, and 100 nm by increasing the deposition time from 200, 400, 600, to 800) seconds. The NiO–Ag-800 recorded the lowest band gap of 3.36 eV, whereas the NiO–Ag-200 recorded the highest band gap of 3.81 eV. The deposited thin films were used as electrocatalysts for methanol oxidation. Its physical properties facilitate the adsorbed reactions, allow for easier penetration of electrolytes, and help in rapid reaction kinetics. Moreover, because Ag–NiO is deposited on an FTO substrate with outstanding adhesion and excellent electric contact, it can be utilized; without adding any binder or conducting agents. The films displayed reduced onset potential for oxidation of the methanol, high current density, and long-term stability. The thickness of the thin film proved that it plays a role in electroactivity. The efficiency of the films increased with increasing thickness, where the Ag–NiO-800 record the lowest onset potential is 0.37 V vs. Ag/AgCl.

Effective ethanol-to-CO2 electrocatalysis at iridium-bismuth oxide featuring the impressive negative shifting of the working potential

Since low overpotential for the anodic ethanol oxidation reaction (EOR) can favor the higher output voltage and power of direct ethanol fuel cells (DEFCs), it is critical to design new EOR catalysts with efficient ethanol-to-CO2 activity at low applied potentials. Thereby, carbon-supported Ir-Bi2O3 (Ir-Bi2O3/C) catalysts with highly dispersive bismuth oxide on the iridium surface are designed and prepared, which can merit splitting the ethanol C–C bond and promoting the oxidation of C1 intermediates at the bifunctional interfaces. The as-obtained Ir-Bi2O3/C catalysts show superior EOR mass activity of up to ca. 2250 mA mg−1Ir. Moreover, they exhibit the record lowest onset oxidation potentials (0.17–0.22 V vs. RHE) and the peak potential (ca. 0.58 V vs. RHE), being 130–300 mV lower than the previous landmark noble metallic catalysts. Furthermore, an apparent C1 pathway faraday efficiency (FEC1) of 28% ± 5.9% at 0.5 V vs. RHE can be obtained at Ir-Bi2O3/C. This work might provide new insights into the new anodic EOR catalysts for increasing the power of DEFCs.

Enhancing photoelectrochemical water oxidation activity of BiVO4 photoanode through the Co-catalytic effect of Ni(OH)2 and carbon quantum dots

The CQDs + Ni(OH)2/BiVO4 photoanode was fabricated by introducing CQDs with fluorescence and optical properties. The CQDs + Ni(OH)2/BiVO4 photoanode exhibited a low water oxidation onset potential (∼0.2 V vs. RHE) and a photocurrent density of 3.05 mA cm−2 at a voltage of 1.23 V vs. RHE, which is about 2.5 times than that of the unmodified BiVO4 electrode, and the charge injection efficiency is 65%. Surface dynamics test showed that CQDs + Ni(OH)2/BiVO4 photoanode had higher charge transfer rate and lower charge recombination rate than BiVO4 electrode. As a cheap and stable catalyst for water oxidation, Ni(OH)2 combined with CQDs can effectively improve the migration of photogenerated electrons and holes, thereby improving the photoelectrochemical (PEC) water oxidation activity of the photoanode.

Delafossite-based nitrate treatment for fabricating copper-cerium hybridized interface to achieve enhanced methanol oxidation reaction

A major concern for direct methanol fuel cells is the deactivation of irreplaceable Pt-based anode catalysts. Herein, a simple cerium nitrate hydrothermal treatment was employed to fabricate a copper-cerium hybridized interface that efficiently utilized the characteristic of Cu release from layered Cu-based delafossite. Remarkably, the construction of hybridized interface considerably utilized ligand effect, strain effect, and bifunctional effect of loaded Pt, yielding the mass activity of 1268.6 mA/mgPt and specific activity of 1.57 mA/cm2, which were 3.69, 1.54 times higher than commercial Pt/C, respectively. Meanwhile, nitrate-treated CeT-rGO-Pt achieved a satisfactory anti-CO poisoning ability as evidenced by a high If/Ib ratio (1.86) and a low CO oxidation onset potential (less than Pt/C 55 mV). Density functional theory calculations further confirmed that the formation of hybridized interface optimized the geometry and electronic structure of Pt, which was favorable for inhibiting carbon monoxide adsorption. This straightforward and effective hybridized interface fabricated strategy provided insight into the design of delafossite-based composite catalysts for the high performance of the methanol oxidation reaction.

Insights into Active Sites and Mechanisms of Benzyl Alcohol Oxidation on Nickel–Iron Oxyhydroxide Electrodes

The electrochemical oxidation of bio-derived molecules has recently garnered interest for its potential in opening electrified synthetic pathways toward value-added products. Herein, we investigate the electrochemical conversion of benzyl alcohol (BA) to benzaldehyde and benzoate on nickel–iron (Fe ∼ 7–18%) electrodes as a model system to understand reaction mechanisms and environmental conditions that can transform these molecules. Our results indicate a strong correlation between benzyl alcohol oxidation (BAO) onset potentials and Ni(II/III) redox peak positions, highlighting the potential role that lower oxidation states of nickel, i.e., Ni3+, can play in BAO catalysis. Our work on the Ni2+/3+ system complements mechanisms that involve higher oxidation states of Ni as reported by others. We note that the Ni redox position and thus BAO onset is impacted by Fe incorporation during electrochemistry from unpurified electrolytes, which can resemble standard reactor operating conditions. We perform a systematic computational investigation into BAO and provide density functional theory (DFT) insights into how the redox mechanism has been such a prominent focus of alcohol oxidations. This includes the mode of BA adsorption and the nature of the adsorption site; upon conversion of the Ni2+ surface to active Ni3+ via hydroxyl deprotonation, BAO is thermodynamically downhill. Our DFT study also introduces the possibility of a vacancy-driven mechanism, though expected to be less prevalent during catalysis than the redox mechanism for a Ni3+ surface. Through the systematic investigation of experimental reaction conditions and computational free energy thermodynamics, we have gained valuable insights into BAO reaction mechanisms that inform catalytic activity. Our study opens avenues for further design and development of catalyst active sites for the oxidation of related organic molecules.

Efficient Voltage-Driven Oxidation of Water and Alcohols by an Organic Molecular Catalyst Directly Attached to a Carbon Electrode.

The integration of heterogeneous electrocatalysis and molecular catalysis is a promising approach to designing new catalysts for the oxygen evolution reaction (OER) and other processes. We recently showed that the electrostatic potential drop across the double layer contributes to the driving force for electron transfer between a dissolved reactant and a molecular catalyst immobilized directly on the electrode surface. Here, we report high current densities and low onset potentials for water oxidation attained using a metal-free voltage-assisted molecular catalyst (TEMPO). Scanning electrochemical microscopy (SECM) was used to analyze the products and determine faradic efficiencies for the generation of H2O2 and O2. The same catalyst was employed for efficient oxidations of butanol, ethanol, glycerol, and H2O2. DFT calculations show that the applied voltage alters the electrostatic potential drop between TEMPO and the reactant as well as chemical bonding between them, thereby increasing the reaction rate. These results suggest a new route for designing next-generation hybrid molecular/electrocatalysts for OER and alcohol oxidations.

Operando Studies of Electrochemical Denitrogenation and Its Mitigation of N-Doped Carbon Catalysts in Alkaline Media.

N-doped carbons (NCs) have excellent electrocatalytic performance in oxygen reduction reaction, particularly in alkaline conditions, showing great promise of replacing commercial Pt/C catalysts in fuel cells and metal-air batteries. However, NCs are vulnerable when biased at high potentials, which suffer from denitrogenation and carbon corrosion. Such material degradation drastically undermines the activity, yet its dynamic evolution in response to the applied potentials is challenging to examine experimentally. In this work, we used differential electrochemical mass spectroscopy coupled with an optimized cell and observed the dynamic behaviors of NCs under operando conditions in KOH electrolyte. The corrosion of carbon occurred at ca. 1.2 V vs RHE, which was >0.3 V below the measured onset potential of water oxidation. Denitrogenation proceeded in parallel with carbon corrosion, releasing both NO and NO2. Combined with the ex situ characterizations and density-functional theory calculations, we identified that the pyridinic nitrogen moieties were particularly in peril. Three denitrogenation pathways were also proposed. Finally, we demonstrated that transferring the oxidation reaction sites to the well-deposited metal hydroxide with optimized loading was effective in suppressing the N leaching. This work showed the dynamic evolution of NC under potential bias and might cast light on understanding and mitigating NC deactivation for practical applications.

Isoindigo-Thiophene D-A-D-Type Conjugated Polymers: Electrosynthesis and Electrochromic Performances.

Four novel isoindigo-thiophene D-A-D-type precursors are synthesized by Stille coupling and electrosynthesized to yield corresponding hybrid polymers with favorable electrochemical and electrochromic performances. Intrinsic structure-property relationships of precursors and corresponding polymers, including surface morphology, band gaps, electrochemical properties, and electrochromic behaviors, are systematically investigated. The resultant isoindigo-thiophene D-A-D-type polymer combines the merits of isoindigo and polythiophene, including the excellent stability of isoindigo-based polymers and the extraordinary electrochromic stability of polythiophene. The low onset oxidation potential of precursors ranges from 1.10 to 1.15 V vs. Ag/AgCl, contributing to the electrodeposition of high-quality polymer films. Further kinetic studies illustrate that isoindigo-thiophene D-A-D-type polymers possess favorable electrochromic performances, including high optical contrast (53%, 1000 nm), fast switching time (0.8 s), and high coloration efficiency (124 cm2 C-1). These features of isoindigo-thiophene D-A-D-type conjugated polymers could provide a possibility for rational design and application as electrochromic materials.

Passivation of Hematite by a Semiconducting Overlayer Reduces Charge Recombination: An Insight from Nonadiabatic Molecular Dynamics.

Hematite (α-Fe2O3) is a promising photoanode material for photoelectrochemical water splitting. Surface-passivating layers are effective in improving water oxidation kinetics; however, the passivation mechanism is not fully understood due to the complexity of interfacial reactions. Focusing on the Fe-terminated Fe2O3 (0001) surface that exhibits surface states in the band gap, we perform ab initio quantum dynamics simulations to study the effect of an α-Ga2O3 overlayer on charge recombination. The overlayer eliminates surface states and suppresses charge recombination 4-fold. This explains in part the observed cathodic shift in the onset potential for water oxidation. The increased charge carrier lifetime is an outcome of two factors, energy gap and electron-vibrational coupling, with a positive contribution from the former but a negative contribution from the latter. This work presents an advance in the atomistic time-domain understanding of the influence of surface passivation on charge recombination dynamics and provides guidance for designing novel α-Fe2O3 photoanodes.

Pd-Ni-B/C Nanocatalysts for Electrochemical Oxidation of Ethanol in Alkaline Media

This paper describes the synthesis of Pd<sub>0.70</sub>-Ni<sub>x</sub>-B<sub>y</sub> nanoparticles (x:y = 0.30:0, 0:0.30, 0.25:0.05, 0.20:0.10, 0.15:0.15, and 0.10:0.20) supported on carbon Vulcan XC-72 R by the chemical reduction method using ethylene glycol as a reducing agent for the study of the electrochemical oxidation of ethanol in alkaline media. Neither surfactants nor templates were used during the syntheses. The catalysts were physically characterized by transmission electron microscopy that showed the formation of nanoparticles with diameters of approximately 3 nm. Analyses of X-ray dispersive energy spectroscopy coupled with scanning electron microscopy identified the presence of the synthesized metals in concentrations close to the nominal ones. The electrochemical study was performed by CO-stripping, cyclic voltammetry, chronoamperometry, and steady-state polarization curves. The catalytic efficiency was also evaluated against the oxidation of CO, which is the principal intermediate adsorbed on the surface of catalysts during ethanol oxidation. The Pd<sub>0.70</sub>Ni<sub>0.15</sub>B<sub>0.15</sub>/C catalyst showed the lowest oxidation onset potentials for both CO (0.37 V) and ethanol oxidation (0.51 V) compared with the Pd/C catalyst (0.63 V and 0.64 V). Chronoamperometric tests also revealed that the Pd<sub>0.70</sub>Ni<sub>0.15</sub>B<sub>0.15</sub>/C catalyst displayed current densities four times higher than those of the Pd/C catalyst, probably because of the electronic and geometric effect that favors the removal of intermediate species from the catalyst surface. The synthesized ternary catalysts were more efficient toward the electrochemical oxidation of ethanol in alkaline media than Pd<sub>0.7</sub>Ni<sub>0.3</sub>/C and Pd/C catalysts. Thus, the synergistic effect of boron on the structure of binary nanoparticle catalysts supported on carbon for use in direct alcohol fuel cells was demonstrated for the first time.

Cationic vacancies accelerate the generation of CoOOH in perovskite hydroxides for the electrooxidation of biomass

SnCo(OH)6 with abundant Sn cation vacancies facilitates the production of deprotonated Co(OH)2 active species and the adsorption of HMF molecules; the onset potential of HMF oxidation is advanced by 200 mV compared to pristine SnCo(OH)6.

Disproportional surface segregation in ligand-free gold-silver alloy solid solution nanoparticles, and its implication for catalysis and biomedicine.

Catalytic activity and toxicity of mixed-metal nanoparticles have been shown to correlate and are known to be dependent on surface composition. The surface chemistry of the fully inorganic, ligand-free silver-gold alloy nanoparticle molar fraction series, is highly interesting for applications in heterogeneous catalysis, which is determined by active surface sites which are also relevant for understanding their dissolution behavior in biomedically-relevant ion-release scenarios. However, such information has never been systematically obtained for colloidal nanoparticles without organic surface ligands and has to date, not been analyzed in a surface-normalized manner to exclude density effects. For this, we used detailed electrochemical measurements based on cyclic voltammetry to systematically analyze the redox chemistry of particle-surface-normalized gold-silver alloy nanoparticles with varying gold molar fractions. The study addressed a broad range of gold molar fractions (Ag90Au10, Ag80Au20, Ag70Au30, Ag50Au50, Ag40Au60, and Ag20Au80) as well as monometallic Ag and Au nanoparticle controls. Oxygen reduction reaction (ORR) measurements in O2 saturated 0.1 M KOH revealed a linear reduction of the overpotential with increasing gold content on the surface, probably attributed to the higher ORR activity of gold over silver, verified by monometallic Ag and Au controls. These findings were complemented by detailed XPS studies revealing an accumulation of the minor constituent of the alloy on the surface, e.g., silver surface enrichment in gold-rich particles. Furthermore, highly oxidized Ag surface site enrichment was detected after the ORR reaction, most pronounced in gold-rich alloys. Further, detailed CV studies at acidic pH, analyzing the position, onset potential, and peak integrals of silver oxidation and silver reduction peaks revealed particularly low reactivity and high chemical stability of the equimolar Au50Ag50 composition, a phenomenon attributed to the outstanding thermodynamic, entropically driven, stabilization arising at this composition.

Electrodeposited Pd nanoparticles on polypyrole/nickel foam for efficient methanol oxidation

The present work describes the Ni foam (Ni–F)/polypyrrole (PPy)/palladium (Pd) (Ni–F/PPy/Pd) multilayered catalysts via a facile electrochemical technique. Potentiostatic deposition of PPy on the surface of Ni–F is followed by galvanostatic deposition of Pd nanoparticles on Ni–F/PPy acted as supports for electrochemical deposition of Pd nanoparticles. The produced catalysts are utilized for electrocatalytic methanol oxidation in alkaline media. Chronoamperometry (CA), cyclic voltammetry (CVs), and electrochemical impedance spectroscopy (EIS) techniques are used to examine the electrocatalytic performance of Ni–F/PPy/Pd based electrodes for methanol oxidation. The polypyrrole modification on Ni–F leads to an improvement in the electrocatalytic activity of the Ni-F/PPY-Pd catalysts toward methanol oxidation. As an open-pored, porous metal with high electrical conductivity, nickel foam produces a substantial amount of active area during the modification of Pd and polypyrrole, which results in significant catalytic activity and a rapid rate charge transfer reaction kinetics on methanol oxidation. The Ni–F/PPy/Pd10 catalyst exhibits enhanced specific activity than its counterparts and a reduced onset potential for methanol oxidation, as well as a low Tafel slope. Based on these results, Ni–F/PPy/Pd10 is suggested as a good material for the anode in the electrocatalytic oxidation of methanol.

Ni2P Nanoparticle-Inserted Porous Layered NiO Hetero-Structured Nanosheets as a Durable Catalyst for the Electro-Oxidation of Urea.

The electro-oxidation of urea (EOU) is a remarkable but challenging sustainable technology, which largely needs a reduced electro-chemical potential, that demonstrates the ability to remove a notable harmful material from wastewater and/or transform the excretory product of humans into treasure. In this work, an Ni2P-nanoparticle-integrated porous nickel oxide (NiO) hetero-structured nanosheet (Ni2P@NiO/NiF) catalyst was synthesized through in situ acid etching and a gas-phase phosphating process. The as-synthesized Ni2P@NiO/NiF catalyst sample was then used to enhance the electro-oxidation reaction of urea with a higher urea oxidation response (50 mA cm−2 at 1.31 V vs. RHE) and low onset oxidation potential (1.31 V). The enhanced activity of the Ni2P@NiO/NiF catalyst was mainly attributed to effective electron transport after Ni2P nanoparticle insertion through a substantial improvement in active sites due to a larger electrochemical surface area, and a faster diffusion of ions occurred via the interactive sites at the interface of Ni2P and NiO; thus, the structural reliability was retained, which was further evidenced by the low charge transfer resistance. Further, the Ni2P nanoparticle insertion process into the NiO hetero-structured nanosheets effectively enabled a synergetic effect when compared to the counter of the Ni2P/NiF and NiO/NiF catalysts. Finally, we demonstrate that the as-synthesized Ni2P@NiO/NiF catalyst could be a promising electrode for the EOU in urea-rich wastewater and human urine samples for environmental safety management. Overall, the Ni2P@NiO/NiF catalyst electrode combines the advantages of the Ni2P catalyst, NiO nanosheet network, and NiF current collector for enhanced EOU performance, which is highly valuable in catalyst development for environmental safety applications.

Electrosynthesis of eco-friendly electrocatalyst based nickel-copper bimetallic nanoparticles supported on poly-phenylenediamine with highest current density and early ethanol oxidation onset potential

Bimetallic catalysts have been investigated as the most efficient materials to accelerate the chemical transformations at the anode in Direct Ethanol Fuel Cells. A comparative study is presented here to synthesize Ni–Cu bimetallic nanoparticles for the ethanol oxidation reaction on three conducting polymers: poly-ortho-phenylenediamine, poly-meta-phenylenediamine, and poly-para-phenylenediamine. X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), and Electrochemical Impedance Spectroscopy (EIS) were used to analyze the modified electrodes. A series of bimetallic Ni–Cu nanoparticles with tunable ratios were successfully synthesized by simply changing the concentrations of Nickel and Copper. It has been confirmed that the best Ni/Cu molar ratio was 25% in the aspect of catalytic performance. The electrocatalyst exhibited an excellent catalytic activity with an anodic current of 70.5 mA cm−2 at the lowest onset potential of 0.39 V with impressive stability. Ni4Cu1/PpPD should be considered as a good alternative to noble metal anode catalyst.

Onset Potential for Electrolyte Oxidation and Ni-Rich Cathode Degradation in Lithium-Ion Batteries.

High-capacity Ni-rich layered metal oxide cathodes are highly desirable to increase the energy density of lithium-ion batteries. However, these materials suffer from poor cycling performance, which is exacerbated by increased cell voltage. We demonstrate here the detrimental effect of ethylene carbonate (EC), a core component in conventional electrolytes, when NMC811 (LiNi0.8Mn0.1Co0.1O2) is charged above 4.4 V vs Li/Li+—the onset potential for lattice oxygen release. Oxygen loss is enhanced by EC-containing electrolytes—compared to EC-free—and correlates with more electrolyte oxidation/breakdown and cathode surface degradation, which increase concurrently above 4.4 V. In contrast, NMC111 (LiNi0.33Mn0.33Co0.33O2), which does not release oxygen up to 4.6 V, shows a similar extent of degradation irrespective of the electrolyte. This work highlights the incompatibility between conventional EC-based electrolytes and Ni-rich cathodes (more generally, cathodes that release lattice oxygen such as Li-/Mn-rich and disordered rocksalt cathodes) and motivates further work on wider classes of electrolytes and additives.

Sustainable Synthesis of Dual Single‐Atom Catalyst of PdN4/CuN4 for Partial Oxidation of Ethylene Glycol

AbstractCatalysts assumed that properly designed bimetallic systems would provide superior catalytic performance due to the cooperative effects between two atoms. Dual single‐atom catalyst (DSAC) PdN4/CuN4 is synthesized using a simple, cost‐effective, and efficient electrochemical reduction method. The palladium single‐atom is prepared first by electrochemical reduction of copper phthalocyanine to create defective N4 sites. The new structural feature is characterized by copper reduction from Cu‐N4 coordination and the formation of defected N4 (▫M‐N4) sites, which react with a Pd precursor and form PdN4 on the host surface. The DSAC PdN4/CuN4 technique synergistically improves electrocatalytic performance toward the ethylene glycol oxidation reaction. It possesses excellent glycolate selectivity (above 88%) in an alkaline solution with an onset oxidation potential as low as 0.6 V versus a reversible hydrogen electrode, compared to commercial Pd/C. The DSAC electrocatalyst is characterized by its high current density of 83.92 mA cm−2 and high faradic efficiency value (>80%) for glycolate at 1.0 VRHE. The findings suggest a promising method to synthesize the DSACs in varying transition metals to achieve highly efficient, selective, and environmentally friendly catalysts for different applications.

Optical, electrochemical and DFT studies of donor-acceptor typed indole derivatives

The donor-acceptor type indole chromophore motif presents an interesting molecular architecture to the scientific world, unfortunately, as in every special and beautiful formation needed; their synthesis represents a synthesis challenge. In the current search, new donor-acceptor typed indole derivatives, 1-methyl-phenyl-3-aldehyde indole (HAN-1), 2-((1-methyl-2-phenyl-1H-indol-3-yl)methylene)malononitrile (HAN-2), 1-ethyl-2-phenyl-3-aldehyde indole (HAN-3), 2-((1-ethyl-2-phenyl-1H-indol-3-yl)methylene)malononitrile (HAN-4) were successfully synthesized and the results supported with FTIR and NMR spectra analysis. All the molecules undergo excited state intramolecular electron transfer with unique charge transfer reaction. Their electrochemical and optical properties were investigated in relation to the acceptor effect of functional groups on the indole units in the conjugated structure. Density functional theory (DFT) calculations exhibited that higher electron withdrawing ability strength resulted in decreased HOMO-LUMU gaps of the molecules. Futhermore, donor acceptor typed indole derivatives undergo irreversibly one electron oxidation in the medium of 0.1 M TBAPF6/ACN solution with a similar onset oxidation potentials. Both experimental and theoretical studies showed that the electron withdrawing ability of the molecules affect more LUMO energy level of the molecules. Moreover, they suggest that donor acceptor indole molecules herein are potential candidates for fabrication of dye synthesized solar cells.

Investigation of electrochemical synthesis temperature effect of the binary transition metals sulfide on nickel foam in water oxidation study

In this work, nickel foam electrode has been used as a substrate for electrochemical synthesis of the binary transition metals sulfide such as nickel and cobalt. Studies showed that the temperature of electrochemical synthesis of binary sulfides has a great effect on their structure and behavior. Therefore, electrochemical synthesizes were performed at different temperatures from 30 to 80 °C and different concentrations of Thioacetamide. Modified electrodes with NiCo2S4 nanosheet arrays at different temperatures and concentrations were used for oxygen evolution reaction (OER). By using the proposed method, the onset potential for oxidation of water was significantly reduced to 1.42 V versus RHE electrode, and a current density of 10 mA cm−2 was obtained at a scanning rate of 50 mV s−1. Tafel slope of the modified electrode was calculated 26 mV.dec−1. This study was performed in KOH 0.1 M electrolyte using linear sweeping voltammetry. Also, to describe the characteristics and morphology of the synthesized modifier, the electrode surface was examined by scanning electron microscopy, energy-dispersive X-ray, transmission electron microscopy, and X-ray diffraction.

Normalization of the EOR catalytic efficiency measurements based on RRDE study for simply fabricated cost-effective Co/graphite electrode for DAEFCs

• Facile fabrication of low-cost and highly efficient Co/graphite electrocatalyst for direct alkaline ethanol fuel cells (DAEFC). • RRDE study for effective distinction between EOR and OER processes. • Normalized parameters for reliable measuring EOR catalytic efficiency. For the catalytic oxidation of ethanol (EtOH), Co is chronoamperometricaly deposited on graphite (G) from 0.05 M CoCl 2 solution with an optimum potential of −1.1 V for 1000 s. The optimum produced Co/G (opt.) electrode yields an ethanol oxidation onset potential (Et-E onset ) 1.43 V/RHE and a current density, I at 1.6 V/RHE = 26.58 mA.cm −2 at a scan rate of 50 mV.s -1 . Its cyclic voltammetry (CV) and rotating ring-disc (RRDE) responses, in solutions of 0.5 M NaOH without and with 1 M EtOH, show the priority of ethanol oxidation reaction (EOR) rather than the oxygen evolution reaction (OER) or transformation of CoOOH to CoO 2 in the potential range 1.4 ≤ E ≤ 1.8 V/RHE. The RRDE responses are used to distinguish between EOR and OER currents in presence of ethanol. The present study includes sincere efforts to resolve the controversy about the measurement of the ethanol oxidation activity parameters. In addition, Co/G (opt.) electrode shows remarkable activity and stability for OER in absence of EtOH. Its overpotential required to achieve 10 mA.cm −2 ( η t = 0 ) is 0.38 V; while, after 24 h, (η t=24h ) is 0.40 V. These values are a noteworthy outcome for our easy and straightforward fabrication method for such an efficient EOR/OER electrocatalyst expending low-cost materials when compared with the previously published work.