Methanol Electro-oxidation Reaction Research Articles

Methanol electrooxidation performance of nickel-modified polyaniline thin films for direct methanol fuel cells

A metal–organic composite thin film composed of polyaniline (PANI) and Ni was prepared and characterized for methanol electrooxidation reaction. First, PANI thin films were electrodeposited on a fluorine-doped tin oxide (FTO) coated glass support in an aqueous acidic solution. Subsequently, the polymer film was modified with Ni particles (FTO/PANI-Ni) by chronoamperometric (CA) technique. The composite film was characterized by structural, morphological and electrocatalytic analyses. X-ray diffraction (XRD) results confirmed the crystallization of Ni according to the cubic structure. Scanning electron microscopy (SEM) images showed that the Ni nanoparticles were uniformly dispersed on the PANI surface. The electrocatalytic performance of the FTO/PANI-Ni composite electrode for the methanol electrooxidation reaction was investigated in 0.5 M KOH solution containing methanol using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and chronoamperometry (CA) techniques. The effects of temperature and methanol concentration on the methanol electrooxidation performance were also studied. The modified composite catalyst exhibited an electrochemically active surface area of 0.5235 cm2. The presence of Ni nanoparticles on the polymer surface promoted the adsorption of methanol molecules and facilitated the oxidation process, leading to higher current densities and better overall performance. The maximum current density was 14 mA cm-2 and the electrode maintain 68 % of its initial activity even after 200 cycles, indicating that the FTO/PANI-Ni electrode exhibited good stability. The high methanol oxidation performance of the composite electrode was associated with large real surface area, a possible synergistic effect between the polymer moleucles and Ni particles as well as high intrinsic activity of Ni for this process.

Wet-Chemical Synthesis of Concave Hexoctahedral Pd and Pd@Pt Nanocrystals for Methanol Electrooxidation.

Nanocrystals (NCs) exposed with high-index facets usually show enhanced electrocatalytic performances. However, it is a great challenge to persevere with high-index facets against their high surface energy during the synthesis. Herein, we successfully synthesize concave hexoctahedral (c-HOH) Pd NCs exposed with 48 high-index {741} facets using a facile one-pot wet-chemical protocol. Control experiments illustrate that l-ascorbic acid plays a critical role in the formation of the c-HOH morphology, acting as both reducing and capping agents. Moreover, we can extend the synthesis for fabricating c-HOH Pd@Pt core-shell NCs by simply introducing a Pt precursor into the reaction solution, attaining remarkably boosted electrocatalysis for methanol electrooxidation reaction (MOR). Integrating the merits of {741} facets, concave structure, and ligand and strain effect of the core-shell structure, c-HOH Pd4@Pt1 core-shell NCs showed an excellent MOR mass activity of 1.18 A mgPGM-1 or 3.60 A mgPt-1, which is 3.80 or 11.61 times higher than that of commercial Pt/C, respectively.

Unraveling the impact of temperature on the reaction kinetics of the electro-oxidation of methanol on Pt(1 0 0)

Methanol is one of the key molecules in the challenge towards a sustainable future, particularly as a renewable hydrogen carrier fuel and as a low-carbon and net carbon-neutral liquid chemical. For most applications, it is imperative to understand the impact of temperature on the methanol electro-oxidation reaction (MEOR). In this study, the influence of the temperature on the kinetics of the MEOR and the parallel reaction pathways is assessed by investigating responses in both conventional and oscillatory regimes using a single-crystal Pt(100) electrode. Our findings demonstrate that chronoamperometric measurements under steady-state conditions provide more reliable values for apparent activation energies compared to transient conditions. Furthermore, a temperature-dependent shift in the dominance of specific oxidation pathways is observed, analogous to a kinetic and thermodynamic control mechanism, preventing the complete poisoning of the electrode surface. Specifically, oxidation pathways leading to the formation of reaction byproducts predominate at lower temperatures, while the oxidation pathway via COad becomes dominant at temperatures exceeding 30 °C. Moreover, our research shows that, at shorter times, temperature changes minimally affect the mean potential required to sustain the applied current during the oscillations in a galvanostatic experiment, which is closely linked with the voltaic efficiency. However, over longer periods, when mass transport phenomena become significant and mixed-mode oscillations occur, elevated temperatures increase the mean potential, resulting in reduced voltaic efficiency. Therefore, to facilitate the complete conversion of methanol to CO2 without increasing the mean potential for current maintenance, it is essential not only to increase the temperature but also to improve the mass transport conditions to mitigate the mixed-mode oscillations, despite their lower minima reached during oscillation. This idea challenges the conventional assumption that a lower minimum potential implies a lower mean potential during oscillations. This advancement propels our understanding to a more sophisticated level, providing valuable insights to guide the materials design to increase the conversion efficiency and optimize the operating temperature of devices crucial to energy conversion.

Stable and active methanol oxidation via anchored PtRu alloy nanoparticles on NiFe layered double hydroxides

Enhancing the catalytic efficiency of the methanol electro-oxidation reaction (MOR) holds paramount importance in expediting the commercialization of direct methanol fuel cells (DMFCs).

Nickel and cobalt-based tungstate nanocomposites as promising electrocatalysts in alkaline direct methanol fuel cells.

In this work, a non-precious group metal (non-PGM) electrocatalyst based on transition metals is introduced as a promising solution for enhancing the efficiency of direct methanol fuel cell (DMFC). Nickel-cobalt mixed tungstate was prepared using a simple co-precipitation method with different molar ratios of Ni, Co and W. The prepared materials were tested and validated using different characterization techniques. It was observed using SEM that the materials are agglomerated amorphous random circular nanocomposite structures. The electrochemical performance of the prepared electrocatalysts revealed that the best nanocomposite was the one with the Ni : Co : W ratio of 1 : 1 : 1.5 (W1.5). This composite showed a higher current density of 229 mA cm-2 towards methanol oxidation at a scan rate of 50 mV s-1 in 1 M methanol at 0.6 V, with the lowest onset potential of 0.33 V. The obtained results present a new strong non-PGM material for direct methanol electro-oxidation reactions and open new doors for economic and earth-abundant electrocatalysts as an alternative to expensive commercially available catalysts.

Electro-Oxidation Reaction of Methanol over La2-xSrxNi1-y(Mn/Fe/Co)yO4+δ Ruddlesden-Popper Oxides.

Solution combustion-synthesized Ruddlesden-Popper oxides La1.4Sr0.6Ni0.9(Mn/Fe/Co)0.1O4+δ were explored for the methanol electro-oxidation reaction. With optimal doping of Sr2+ in the A site and Co2+ in the B site, Ni3+ with t2g6 configuration in La1.4Sr0.6Ni0.9Co0.1O4+δ exhibited a tetragonal distortion with compression in axial bonds and elongation in equatorial bonds. This structural modification fostered an augmented overlap of orbitals with axial O 2p orbitals, leading to a heightened density of states at the Fermi level. Consequently, this facilitated not only elevated electrical conductivity but also a noteworthy reduction in the charge transfer resistance. These effects collectively contributed to the exceptional methanol oxidation activity of La1.4Sr0.6Ni0.9Co0.1O4+δ, as evidenced by an impressive current density of 21.4 mA cm-2 and retention of 95% of initial current density even after 10 h of prolonged reaction. The presence of Ni3+ further played a pivotal role in the creation of NiOOH, a crucial intermediate species, facilitated by the presence of surface oxygen vacancies. These factors synergistically enabled efficient methanol oxidation. In summary, our present study not only yields substantial insights but also paves the way for a novel avenue to fine-tune the activity of Ruddlesden-Popper oxides for the successful electro-oxidation of methanol.

Tuning intrinsic strain in PtCuCr nanoframes boosts electro-oxidation of liquid fuels

Modulating the intrinsic strain of metal catalysts has become one of the most powerful strategies to boost the electro-catalytic properties. Herein, we report PtCuCr nanoframes (NFs) with tunable surface strain synthesized by different heating model. PtCuCr h-NFs (hexapod NFs) exhibit ∼ 2.3% compressive strain compared to PtCuCr d-NFs (dendrite NFs). The compressive strain modulates the electronic structure (e.g., d-band center) of PtCuCr NFs and endows them with superior activity toward the methanol and formic acid electro-oxidation reactions (MOR and FAOR). Particularly, the specific activities of PtCuCr h-NFs for MOR and FAOR are 4.13 mA cm−2 and 1.12 mA cm−2, respectively, which are 1.35 and 1.84 times higher than those of PtCuCr d-NFs. Mechanistic studies reveal that compression on the surface of PtCuCr h-NFs can weaken the bonding strengths of CO species as well as contributed to the oxidation of CO by OH species, resulting in an improved anti-CO-poisoning capability.

Ni‐Pt Bimetallic Alloy Nanoparticles Dispersed Uniformly on Carbon Nanotubes for Efficient Electrooxidation Methanol

AbstractIn this paper, Ni−Pt bimetallic alloy nanoparticles were loaded on carbon nanotubes to construct Ni−Pt nanoparticles/carbon nanotubes (Ni−Pt NPs/CNTs) composites as excellent catalytic materials for methanol electrooxidation reaction (MOR). X‐ray diffraction (XRD), X‐ray photoelectron spectroscopy (XPS), and special aberration corrected transmission electron microscope (STEM) were employed to investigate the morphology of the material. It was confirmed that the Ni−Pt alloy nanoparticles dispersed uniformly on the surface of carbon nanotubes. The activity and stability of Ni−Pt NPs/CNTs composites were measured by chronoamperometry (CA), linear sweep voltammetry (LSV) and cyclic voltammetry (CV). The catalytic performance was explored by adjusting the ratio of Ni to Pt. The Ni1Pt2 NPs/CNTs composite showed excellent performance for MOR. Its mass activity for MOR was 1255 mA ⋅ mg−1Pt, which was 2.76, 2.56 times as that of commercial Pt/C, Pt black catalyst, respectively. Moreover, the resistance to CO toxicity of Ni1Pt2 NPs/CNTs composite was better than commercial Pt/C and Pt black catalyst.

NiFe2O4/Ti3C2 nanocomposite as an efficient catalyst for methanol electro-oxidation reaction: Investigating annealing temperature and synergetic effect

In the present work, NiO/Ti3C2, γ-Fe2O3/Ti3C2, and NiFe2O4/Ti3C2 nanocomposites were prepared via hydrothermal method. The influence of annealing temperature on the crystalline structure and subsequently, on the electrocatalytic performance was investigated by characterization and electrochemical processes. The presence of Ti3C2 Mxene substrate improved the electron transfer kinetics of NiFe2O4 spinel nanoparticles. In addition, due to the synergistic effect of nickel and iron elements in the structure of NiFe2O4, the NiFe2O4/Ti3C2 nanocomposite showed better electrochemical activity and stability compared to the single metal oxides (NiO and γ-Fe2O3). Based on the results, NiFe2O4/Ti3C2 nanocomposite annealed at 200 °C, showed the highest current density (24 mA cm−2) and the most stable catalytic performance (90.6%) compared to other temperatures. This nanocatalyst can be proposed as a promising catalyst for methanol oxidation reactions in direct alcohol fuel cells.

Methanol assisted water electrooxidation on noble metal free perovskite: RRDE insight into the catalyst’s behaviour

In this work, we have hypothesized that noble metal-free perovskites are an essential class of oxygen evolution reaction (OER) catalysts in an alkaline medium and thus, they are a suitable candidate for the assisted water oxidation catalysts. Herein, we demonstrate that the origin of the methanol-assisted OER activity at near thermodynamic potential on perovskite electrode arises due to the involvement of additional hydroxyls as a result of dissociative chemisorption of methanol. When the perovskite electrode is screened for methanol electrooxidation reaction in 0.5 M KOH + 0.5 M methanol electrolyte, it delivers a two times higher current density. This imparts an 82 % increase in the evolution of oxygen gas moles with complete oxidation of methanol to carbon dioxide. Along with the electrochemical characterization to understand the electrocatalyst property, Rotating ring disk electrode (RRDE) technique is explored for the first time in literature to validate the catalyst’s involvement during OER. RRDE is effective in understanding the lattice oxygen behaviour and methanol-assisted water electrooxidation during OER. Our results suggest new insights and ideas towards the oxygen evolution reaction process and the mechanistic insight into the elevated OER due to assisted methanol electrooxidation.

Mass transfer phenomena induced by surface gas flow rate in the hanging meniscus configuration: A case study of the methanol electro-oxidation reaction on Pt(100)

Mass transfer phenomena induced by surface gas flow rate in the hanging meniscus configuration: A case study of the methanol electro-oxidation reaction on Pt(100)

Nanostructure-induced inhibition of oxygen evolution and enhancement of methanol electrooxidation on engineered anodized brass

To capitalize the improved electrical contact feature, a self-supported hybrid binary/ternary copper and zinc oxides (i.e., ZnO–Cu2O and Cu2O–ZnO–CuO) nanostructures have been generated via a simple potentiostatic mode of anodaization on alpha brass in an alkaline medium. The catalyst nanostructuring i.e., wheat-grain-like to nanograss type structure has improved the mass transport, sluggish kinetics of methanol electrooxidation reaction process, and hindered the competitive oxygen evolution reaction (OER) of direct methanol fuel cell. The catalytic poisoning phenomenon has not been noticed due to two different reaction processes in two potential regions. Interestingly, a significant reduction in overpotential (η10mAcm−2OER−CH3OH) has been noticed for S125@A1 and S125@A2 samples i.e., 236 mV and 350 mV, respectively. The enhancement of current density has been explained through inductive circuit perspective. So, the present study provides a better insights to design and utilize non-precious metal/alloy based catalyst with hindered OER and enhanced methanol electrooxidation reaction activity.

Copper selenide nanobelts an electrocatalyst for methanol electro-oxidation reaction

Energy crisis of the current society have attract the research attention for alternative energy sources. Methanol oxidation is source of energy but need efficient electrocatalyst like Pt. However, their practical ability is hinder due to cost and poisoning effect. In this regard, efficient catalyst is required for methanol oxidation. Herein, high temperature, pressure, and diethylenetryamine (DETA) as reaction medium/structure directing agent during solvothermal method are used for nanobelt Cu3Se2/Cu1.8Se (mostly hexagonal appearance) formation. The electrocatalyst shows optimized methanol electrooxidation reaction (MOR) response in 1 M KOH and 0.5 M methanol at scan rate of 50 mV/s and delivers a current density 7.12 mA/mg at potential of 0.65 V (vs Ag/AgCl). The catalyst exhibits high electrochemical active surface area (ECSA) (0.088 mF/cm2) and low Rct with good stability for 3600 s which favor its high MOR performance. This high response is due to its 2D hexagonal nanobelt morphology, which provides large surface area for reaction. The space among nanobelt reduce diffusion kinetics and rough/irregular edge increase reaction site to overall improve the methanol oxidation reaction.

Tailoring the electronic structure of PtNi nanoalloy for boosting methanol electro-oxidation reaction

Tailoring the electronic structure of Pt-based catalysts can effectively facilitate their methanol oxidation reaction (MOR). Despite a great deal of effort, the fabrication of Pt-based catalysts with both tunable electronic structure and well-dispersion is still challenging. Herein, the PtNi alloy nanoparticles supported on poly (3, 4-ethylenedioxythiophene) modified multi-walled carbon nanotubes (PtNi/PEDOT-MWCNTs) was prepared for MOR. Transmission electron microscopy reveals the successful synthesis of PtNi nanoparticles (3.5 nm) by the reduction of H2. The X-ray photoelectron spectroscopy confirmed the strong electronic interaction between Ni and Pt, and the electronic environment of Pt atoms can be tailored by alloying different atomic content of Ni. Thus, the obtained PtNi/PEDOT-MWCNTs was suitable to design an effective electro-catalyst. As revealed through the electrochemical measurements, the fabricated PtNi/PEDOT-MWCNTs catalyst displayed higher peak current density, better stability, and excellent CO-tolerance than those of Pt nanoparticles dispersed on PEDOT-MWCNTs, MWCNTs, and commercial carbon black. The surface/interface engineering tactic highlights the tailoring of the electronic structure of Pt-based catalysts, which can be applied in various fields, including methanol fuel cells and other catalytic reactions.

Formation mechanism of macroporous Cu/CuSe and its application as electrocatalyst for methanol oxidation reaction

Single-step solvothermal method is used to prepare Cu/CuSe as an electrocatalyst for methanol electro-oxidation reaction (MOR). 1,3-butan-diol is selected as a reaction medium, whose viscosity and complex formation with Cu(II) ions dictate the catalyst morphology. The catalyst has a macroporous structure, which is composed of nanoballs with a high purity, crystallinity, and uniform morphology. The electrocatalyst is excellent for MOR, as it delivers current density of 37.28 mA/mg at potential of 0.6 V (vs Ag/AgCl) in the electrolyte of 1 M KOH and 0.75 M methanol at a 50 mV/s scan rate under conditions of cyclic voltammetry. The catalyst also shows good stability for 3600 s with negligible charge transfer resistance and high electrochemical active surface area (ECSA) value of 0.100 mF/cm2.

Tuning the morphology of sputter-deposited platinum catalyst: From compact layers to dispersed nanoparticles

A comprehensive study on adjusting the morphology of sputter-deposited platinum was performed. Platinum was deposited under various Ar pressure ranging from 0.3 to 3.2 Pa using a conventional magnetron system as well as at 57 Pa using a gas aggregation cluster source integrated into the magnetron sputtering system. The morphology and structure of deposited layers were characterized with a broad portfolio of characterization techniques such as scanning electron microscopy, transmission electron microscopy, grazing incidence small angle X-ray scattering and X-ray diffraction. The results revealed a continuous evolution of the Pt layer morphology from a thin-film-like layer of tightly packed Pt nanoparticles to a deposit composed of dispersed particles of 5-7 nm in size as the Ar pressure increased. The electrochemically active surface area of deposited Pt, as calculated from cyclic voltammograms, increased with deposition pressure from 11.7 m2·gPt−1 to 22.3 m2·gPt−1 and 24 m2·gPt−1 for Pt deposited at 0.3, 3.2 and 57 Pa, respectively. This increase in active sites was reflected in a significant improvement in the mass activity of platinum exemplary confirmed using a methanol electrooxidation reaction.

Electronic and Coordination Effect of PtPd Nanoflower Alloys for the Methanol Electrooxidation Reaction

Platinum-based electrocatalysts usually exhibit limited and quickly vanished activity for the methanol oxidation reaction (MOR) due to active site occupation and surface intermediate poisoning, especially CO. The attendant synergistic effect of the alloy strategy is often executed to improve these flaws. Here, PtPd nanoflower alloys uniformly anchored on the carbon paper were successfully synthesized by electrodeposition to construct well-defined active sites, over which high MOR activity and tolerance were realized. The homogeneous alloy structure of PtPd nanoflowers was confirmed by TEM and XAFS. Impressively, the Pt1Pd1-N NFs/CP exhibited an excellent mass activity of 9.25 A mgPt+Pd–1 and specific activity of 13.2 mA cmECSA–2 of MOR in the alkaline electrolyte, and 87.8% of the initial activity was still retained after 500 cycles. In situ infrared spectroscopy revealed that Pt1Pd1-N NFs/CP ensured the complete oxidation of methanol following a CO-free path. The investigation of the electronic and coordination structure demonstrated that the Pt–Pd adjacent sites with a zero valence are the highly active center for MOR, and the synergistic effect between Pt and Pd greatly improved the MOR electrocatalytic performance. This work offers an effective strategy to precisely control the number and structure of decorating species for constructing alloy nanocatalysts to enhance the electroactivity toward MOR.

Enhancing electrocatalytic methanol oxidation of Pd-Ir nanoalloy through electron-rich catalytic interface induced by incorporating phosphorus

Incorporating less expensive nonmetal phosphorus (P) into noble metal-based catalysts has become a developing strategy to enhance the catalytic performance of electrocatalysts for methanol electrooxidation reaction (MOR), attributing to the electronic and synergistic structure alteration mechanism. In the work, three-dimensional nitrogen-doped graphene anchoring ternary Pd-Ir-P nanoalloy catalyst (Pd7IrPx/NG) was prepared by co-reduction strategy. As a multi-electron system, elemental P adjusts the outer electron structure of Pd and diminishes the particle size of nanocomposites, which heightens the electrocatalytic activity effectively and accelerate MOR kinetics in alkaline medium. The study reveals that the electron effect and ligand effect induced by P atoms on the hydrophilic and electron-rich surface of Pd7Ir/NG and Pd7IrPx/NG samples can reduce the initial oxidation potential and peak potential of COads, showing significantly enhanced the anti-poisoning ability compared with commercial Pd/C as the benchmark. Meanwhile, the stability of Pd7IrPx/NG is significantly higher than that of commercial Pd/C. The facile synthetic approach provides an economic option and a new vision for the development of electrocatalysts in MOR.

Molybdenum Carbide/Ni Nanoparticles Embedded into Carbon Nanofibers as an Effective Non-Precious Catalyst for Green Hydrogen Production from Methanol Electrooxidation.

Molybdenum carbide co-catalyst and carbon nanofiber matrix are suggested to improve the nickel activity toward methanol electrooxidation process. The proposed electrocatalyst has been synthesized by calcination electrospun nanofiber mats composed of molybdenum chloride, nickel acetate, and poly (vinyl alcohol) under vacuum at elevated temperatures. The fabricated catalyst has been characterized using XRD, SEM, and TEM analysis. The electrochemical measurements demonstrated that the fabricated composite acquired specific activity for methanol electrooxidation when molybdenum content and calcination temperature were tuned. In terms of the current density, the highest performance is attributed to the nanofibers obtained from electrospun solution having 5% molybdenum precursor compared to nickel acetate as a current density of 107 mA/cm2 was generated. The process operating parameters have been optimized and expressed mathematically using the Taguchi robust design method. Experimental design has been employed in investigating the key operating parameters of methanol electrooxidation reaction to obtain the highest oxidation current density peak. The main effective operating parameters of the methanol oxidation reaction are Mo content in the electrocatalyst, methanol concentration, and reaction temperature. Employing Taguchi's robust design helped to capture the optimum conditions yielding the maximum current density. The calculations revealed that the optimum parameters are as follows: Mo content, 5 wt.%; methanol concentration, 2.65 M; and reaction temperature, 50 °C. A mathematical model has been statistically derived to describe the experimental data adequately with an R2 value of 0. 979. The optimization process indicated that the maximum current density can be identified statistically at 5% Mo, 2.0 M methanol concentration, and 45 °C operating temperature.

High-performance Mo2C/MWCNT electrocatalyst for MOR: Comparison with MoO2/MWCNT and MoO3/MWCNT

Methanol oxidation reaction (MOR) in the direct methanol fuel cells involves six electron transfer processes, and noble metal based catalysts such as Pt and Pd are still recognized as efficient catalysts for MOR. It is generally accepted that the reaction is mainly related to the d states of precious metal-based catalysts. Transition metal carbides and noble metals exhibit similar d band structure and catalytic properties, among which molybdenum carbide is an effective catalyst. However, molybdenum carbide-based catalysts have not been used in methanol electrooxidation reactions until the present moment, and we tried to use Mo2C/MWCNT for the MOR reaction. Compared with MoO2/MWCNT and MoO3/MWCNT, it is found that Mo2C/MWCNT shows the highest electrocatalytic activity, and the current density of Mo2C/MWCNT is 185 mA cm−2 in 1 M KOH+1 M CH3OH at 0.70 V (vs. Hg/HgO). The current density is about 2.2 times and 1.4 times higher than those of MoO2/MWCNT and MoO3/MWCNT catalysts, respectively, and the electrochemical impedance also decreases markedly. The current density retains 76.19% of the initial catalytic activity after 10 h at the Mo2C/MWCNT electrode, indicating that the catalyst has superior stability for MOR. The reaction pathway of MOR on Mo2C/MWCNT is as follows: CH3OH∗ → CH3O∗→ CH2O∗ → CH2OOH∗ → CH2OO∗ → CHOO∗ → CO2∗. The result not only expands the Mo2C application area, but also provides a new idea for the design of the MOR catalyst.