Electrocatalytic Methanol Oxidation Reaction Research Articles

Effect of transition metals (Ni and Co) in the methanol oxidation reaction electrocatalytic activity on Mo2C/MWCNT

The direct methanol fuel cells still recognize Pt and Pd as efficient catalysts for the methanol oxidation reaction (MOR). Our previous study demonstrated the high activity and stability of the Mo2C/MWCNT catalyst for electrocatalytic MOR. To further enhance the performance of Mo2C/MWCNT, the second metals (Ni and Co) are introduced onto Mo2C/MWCNT. It is found that Ni-Mo2C/MWCNT exhibits the highest electrocatalytic MOR activity, with a current density of 192 mA cm−2 in 1 mol/L(M) KOH + 1 M CH3OH electrolyte at 0.6 V (vs. Hg/HgO). Additionally, the stability of Mo2C/MWCNT significantly improves after Ni doping (85.61 % vs. 76.19 %). Characterization results reveal a strong interaction between Ni species and Mo2C, with some Ni ions doping into Mo2C. Furthermore, the Ni-Mo2C nanoparticles are evenly dispersed on MWCNT, with nanoparticle sizes ranging from 5 to 10 nm. DFT results indicate a charge transfer from Mo2C to Ni, resulting in the shift of the d-band center of the surface away from the Fermi level. Moreover, the interface charge transfer resistances of Ni- Mo2C/MWCNT significantly decreased (7.2 vs. 20.0 Ω). As a result, the electrocatalytic MOR activity on Ni- Mo2C/MWCNT improved compared to Mo2C/MWCNT.

Au-doped PtCu2 nanonetworks with interface-rich for enhancing methanol electro-oxidation performance

Regulating the near-surface structure of platinum-based alloys by inserting transition metal atoms can significantly improve the electro-oxidative performance of small organic molecules. So far, it is rarely reported that a small amount of Au element is introduced into the interior of Pt-based alloys as an active auxiliary to adjust the electrocatalytic activity and stability of Pt-based alloys with special morphologies. Herein, a stable three-dimensional (3D) Au-doped PtCu2/C (Au–PtCu2/C) catalyst with nanonetwork structure and abundant interfaces has been successfully developed, in which the oxyphilic Cu atoms and stable Au atoms are implanted into the whole and inside of the Pt-based nanonetwork, respectively. Detailed physical characterizations of the Au–PtCu2/C catalyst illustrate that the insertion of Au atoms generates core-shell-like nanonetwork, highly-open structure, strong electronic effect, and sufficient active sites. The well-designed Au–PtCu2/C catalyst exhibits superior mass activity (MA) of 2355 mA·mgPt−1 and long-term durability of 500 cycles toward methanol oxidation reaction (MOR) in an acidic medium. Notably, the MA of the Au–PtCu2/C catalyst is 7.3 folds and 1.3 folds that of the Pt/C (322 mA·mgPt−1) and PtCu2/C (1821 mA·mgPt−1) catalysts, respectively. The kinetic and thermodynamics studies indicate that the Au–PtCu2/C catalyst is superior to PtCu2/C and Pt/C catalysts in reducing the electrochemical activation energy of MOR, promoting the mass transfer of methanol molecules, and enhancing electronic conductivity. This work proposes an advanced strategy to fabricate efficient and durable electrocatalyst with excellent electrocatalytic MOR performance, thereby enabling catalysts with special morphology to have greater application potential in direct methanol fuel cell.

Oxygen Vacancies Alter Methanol Oxidation Pathways on NiOOH.

A thorough comprehension of the mechanism underlying the methanol oxidation reaction (MOR) on Ni-based catalysts is critical for future electrocatalytic design and development. However, the mechanism of MOR on these materials remains a matter of controversy. Herein, we combine in situ surface-enhanced infrared absorption spectroscopy (SEIRAS) and density functional theory (DFT) calculations to identify the active sites and determine the mechanism of MOR on monometallic Ni-based catalysts in alkaline media. The SEIRAS results show that formate and (bi)carbonate are formed after the commencement of the MOR with potential-dependent relative distributions. These spectroscopic results are in good agreement with the DFT-computed reaction profiles over an oxygen vacancy, suggesting that the MOR mainly proceeds through the formate-involving pathway, in which the early consumption of methanol yields formate as the major product, while increasing potential drives further oxidation of formate to (bi)carbonate. We also find a parallel pathway for the generation of (bi)carbonate at high potentials that bypasses the formation of formate. The two main pathways are thermodynamically more feasible than the one predominantly reported in the literature for MOR on NiOOH that involves CHO and/or CO as key intermediates. These DFT results are supported by spectroscopic evidence showing that no band associated with CHO or CO can be detected by SEIRAS, which is attributed to the nature of the oxygen vacancies as the active sites, suppressing deep dehydrogenation of CH2O to CHO. This work thus shows the promising role of defect engineering in promoting the electrocatalytic MOR activity and selectivity.

Nanoarchitectonics for modulation on the electronic structure of ultrafine PtRuFe nanowires as robust methanol electrooxidation catalysts

The widespread adoption of Pt-based electrocatalysts in the anode side of direct methanol fuel cell (DMFC) faces challenges stemming from their limited activity, stability, and high cost. Herein, ultrafine PtRuxFey trimetallic nanowires (PtRuxFey NWs) with a diameter of approximately 1.25 nm were synthesized for the electrocatalytic methanol oxidation reaction (MOR). The structure-activity relationship between the electronic structure of PtRuxFey NWs and their electrocatalytic performance was established by meticulously controlling the addition of Ru(acac)3 and Fe(Ac)2. Under optimal conditions, PtRu0.25Fe0.14 NWs displayed remarkable MOR performance, boasting the mass activity (1332.3 mA mgPt−1) and specific activity (1.0 mA cm−2), a 4.0-fold and 1.8-fold enhancement over that of the commercial catalysts. Additionally, after a chronoamperometry test, PtRu0.25Fe0.14 NWs demonstrated a current density 8.3 times higher than that of Pt/C under the same test conditions. The excellent MOR performance of PtRuxFey NWs can be attributed to their one-dimensional and ultrafine structure advantages, the electronic effects of Ru/Fe on Pt, and the bifunctional capabilities. Our research may lead to a simple and controllable strategy that combines various approaches to enhance the performance of Pt-based electrocatalysts in the anode of DMFC.

Construction of an electron-transfer channel via Cu-O-Ni to inhibit the overoxidation of Ni for durable methanol oxidation at industrial current density.

The electrocatalytic methanol oxidation reaction (MOR) is a viable approach for realizing high value-added formate transformation from biomass byproducts. However, usually it is restricted by the excess adsorption of intermediates (COad) and overoxidation of catalysts, which results in low product selectivity and inactivation of the active sites. Herein, a novel Cu-O-Ni electron-transfer channel was constructed by loading NiCuO x on nickel foam (NF) to inhibit the overoxidation of Ni and enhance the formate selectivity of the MOR. The optimized NiCuO x -2/NF demonstrated excellent MOR catalytic performance at industrial current density (E 500 = 1.42 V) and high faradaic efficiency of ∼100%, as well as durable formate generation up to 600 h at ∼500 mA cm-2. The directional electron transfer from Cu to Ni and enhanced lattice stability could alleviate the overoxidation of Ni(iii) active sites to guarantee reversible Ni(ii)/Ni(iii) cycles and endow NiCuO x -2/NF with high stability under increased current density, respectively. An established electrolytic cell created by coupling the MOR with the hydrogen evolution reaction could produce H2 with low electric consumption (230 mV lower voltage at 400 mA cm-2) and concurrently generated the high value-added product of formate at the anode.

Research development of anti-CO poisoning in electrocatalytic methanol oxidation processes: a review

This review examines research advancements in anti-CO poisoning during the electrocatalytic methanol oxidation reaction (MOR).

Nickel 2‐Methylimidazole Metal–Organic Framework Ultrathin Nanosheets/Titanium Carbide MXene Hybrid Nanostructure as a Bifunctional Electrocatalyst for Methanol and Urea Oxidation Reactions

In the development of direct methanol and direct urea fuel cells, efficient electrocatalytic methanol oxidation reaction (MOR) and urea oxidation reaction (UOR) are employed. These approaches are essential in fuel cell technology for addressing the rising global energy and environmental concerns. In this research, nickel 2‐methylimidazole metal–organic framework (Ni‐MOF) and Ni‐MOF‐integrated titanium carbide (Ti3C2) MXene hybrid nanostructures (Ni‐MOF/Ti3C2) were controllably synthesized via a facile solvothermal method. Ti3C2 MXene nanosheets are utilized as two‐dimensional support to enhance the catalytic activity of the Ni‐MOF/Ti3C2 hybrid nanostructure. Furthermore, the methanol and urea electro‐oxidation activity of the Ni‐MOF/Ti3C2 hybrid nanostructure is investigated. The synergistic effect between Ni‐MOF and Ti3C2 MXene resulted in excellent and durable electrochemical performance. Thus, the newly synthesized electrode material exhibited high electrocatalytic activity at 0.8 V vs. Hg/HgO for methanol (166 mA cm−2) and urea electro‐oxidations (161 mA cm−2). The methanol and urea oxidation rates of the Ni‐MOF/Ti3C2‐10 hybrid nanostructure are approximately five and three times higher than that of pure Ti3C2 MXene and pristine Ni‐MOF, respectively. This work provides the potential of the Ni‐MOF‐integrated Ti3C2 MXene hybrid nanostructure as a promising electrocatalyst for MOR and UOR.

Design and catalytic performance of Cu/γ-Al2O3 for electrocatalytic methanol oxidation reaction by using density functional theory and molecular dynamics

The electrocatalytic activity of methanol oxidation reaction (MOR) on Cu/γ-Al2O3 and the growth behavior of Cu on γ-Al2O3 are investigated by using density functional theory and molecular dynamics. It is found that the interaction between the Cu3 cluster and γ-Al2O3(110) is stronger than that between the Cu4 cluster and γ-Al2O3(110). Consequently, the d-band center of the Cu3 cluster locates close to the Fermi level compared to the d-band center of the Cu4 cluster, resulting in high electrocatalytic MOR activity on Cu3/γ-Al2O3(110). The electrocatalytic MOR pathway is non-CO pathway on Cu3/γ-Al2O3(110). The highest Gibbs free energy pathway is CH3O* → CH2O*, which the Gibbs free energy is 0.53 eV. To achieve a high proportion of 2D Cu cluster on γ-Al2O3, it is recommended to prepare the catalyst at temperatures below 500 K with Cu loading below 21.78 wt%. These findings provide valuable insights into the design of MOR catalysts.

Direct Electrocatalytic Methanol Oxidation on MoO3/Ni(OH)2: Exploiting Synergetic Effect of Adjacent Mo and Ni.

Ni-based materials have been widely investigated as methanol oxidation reaction (MOR) catalysts. The formation of NiOOH and its reduction to Ni(OH)2 are generally regarded as essential steps for methanol oxidation. However, in such an indirect route, the efficiency of proton coupled electron transfer is fundamentally limited by the rate of transition from Ni(OH)2 to NiOOH back and forth. Herein we demonstrate a direct MOR pathway on MoO3/Ni(OH)2 without the formation of a NiOOH mediator. The MoO3/Ni(OH)2 exhibits a benchmark electrocatalytic MOR current density of 1000 mA cm-2 at 1.52 V vs. RHE with a nearly 100% faradic efficiency, outperforming all the state of art MOR electrocatalysts. In-situ Raman spectroscopy confirms that NiOOH is not formed during the electrocatalytic MOR process on the MoO3/Ni(OH)2. Density functional theory calculations suggest that Ni2+ in MoO3/Ni(OH)2 serves as the methanol adsorption site while the doped Mo6+ plays a key role in capturing the deprotonated H·. Benefiting from the Mo-Ni synergistic effect, the energy barrier of the CH2O* → CHO* + H* process is significantly reduced, avoiding the NiOOH formation and leading to the direct MOR. Our research unravels a direct electrochemical MOR pathway that does not rely on NiOOH formation and provides a facile strategy of regulating the intermediate process barrier for MOR.

Au Doping PtNi Nanodendrites for Enhanced Electrocatalytic Methanol Oxidation Reaction

To boost the electrocatalytic methanol oxidation reaction (MOR) of Platinum (Pt), making binary PtM (M = transition metals, for example, Fe, Cu, and Ni) with specific morphology is known as a promising method. Although great progress has been made in the synthesis of shaped PtM catalysts toward MOR, enhancing the catalytic performance of the PtM to enable it to be commercialized is still a hotspot. In this work, the Au-doped PtNi dendritic nanoparticles (Au-PtNi DNPs) were obtained by doping a small amount of gold (Au) into initially prepared PtNi DNPs, greatly improving their MOR catalytic activity and durability. The energy-dispersive X-ray spectroscopy mapping (EDXS) indicates that the surface of DNPs is mainly composed of Au dopant and PtNi, while the core is mainly Pt, indicating the formation of Au-doped PtNi/Pt core-shell-like DNP structures. The electrocatalytic performance of the prepared Au-PtNi DNPs with different compositions for the MOR was evaluated using cyclic voltammetry, chronoamperometry, and CO-stripping tests. The experimental findings indicate that the Au-PtNi DNPs showed better MOR performance in comparison with PtNi DNPs and commercial Pt catalysts. Among all the catalysts, 6% Au-PtNi DNPs showed 4.3 times improved mass catalytic activity for the MOR in comparison with commercial Pt catalysts. In addition, all the prepared Au-PtNi DNPs display a remarkable CO tolerance compared to that of PtNi DNPs and commercial Pt catalysts. The dendritic structure of Au-PtNi DNPs can effectively enhance catalytic performance, combined with the electronic effect of Au, Pt, and Ni.

Insights on the Roles of Nitrogen Configuration in Enhancing the Performance of Electrocatalytic Methanol Oxidation over Pt Nanoparticles.

Stabilization of the Pt in N-doped carbon materials is an effective method to improve the performance of electrocatalytic methanol oxidation reaction (MOR). Nevertheless, the roles of different N configurations (pyridinic N, pyrrolic N, and graphitic N) toward the electrochemical performance of Pt-based catalysts remain unclear. Herein, Density Functional Theory calculations are adopted to elucidate the synergistic promotion of MOR by different N-configurations with Pt nanoparticles (NPs). Guided by the theoretical study, a series of MOR electrocatalysts with different ratios of pyridinic N and pyrrolic N (denoted as Pt/N-CNT-X (500, 600, 700, 800, and 900)) are designed and synthesized. Surprisingly, the electrocatalytic activity of Pt/N-CNT-600 with a suitable ratio of pyrrolic-N and pyridinic-N for MOR reaches 2394.7mAmg-1 Pt and 5515.8mAmg-1 Pt in acidic and alkaline media, respectively, which are superior to the Pt/CNTs, commercial Pt/C, and the ever-reported Pt-based electrocatalysts. The strong metal-support interaction induced by the N-doping is the crucial reason for the superior electrocatalytic performance. More importantly, the ability of pyrrolic-N and pyridinic-N in promoting the adsorption and oxidation of CH3 OH and the oxidation of CO* is substantiated for the first time in methanol oxidation. This work provides new insights on the design of efficient electrocatalysts for MOR.

Toward Electrocatalytic Methanol Oxidation Reaction: Longstanding Debates and Emerging Catalysts.

The study of direct methanol fuel cells (DMFCs) has lasted around 70 years, since the first investigation in the early 1950s. Though enormous effort has been devoted in this field, it is still far from commercialization. The methanol oxidation reaction (MOR), as a semi-reaction of DMFCs, is the bottleneck reaction that restricts the overall performance of DMFCs. To date, there has beenintense debate on the complex six-electron reaction, but barely any reviews have systematically discussed this topic. To this end, the controversies and progress regarding the electrocatalytic mechanisms, performance evaluations as well as the design science toward MOR electrocatalysts are summarized. This review also provides a comprehensive introduction on the recent development of emerging MOR electrocatalysts with a focus on the innovation of the alloy, core-shell structure, heterostructure, and single-atom catalysts. Finally, perspectives on the future outlook toward study of the mechanisms and design of electrocatalysts are provided.

Ultrafine high-entropy alloy nanoparticles for extremely superior electrocatalytic methanol oxidation

To develop highly efficient catalysts with low Pt content for electrocatalytic methanol oxidation reaction (MOR) is meaningful yet still challenged. Here, PtPdCdZnCo ultrafine high-entropy alloy (uf-HEA) nanoparticles (∼2.6 nm) were achieved by a facile one-pot chemical synthesis. As MOR catalyst, the uf-HEA displays ultrahigh mass activity of 2.86 and 11.1 A mgPt−1 in acidic and alkaline environments, respectively. That is the best acidic MOR catalyst so far by comparing with other reported Pt-based catalysts. Study suggests the outstanding MOR activity is attributed to the weakened reaction intermediates adsorption on uf-HEA surface.

Passivating Oxygen Evolution Activity of NiFe-LDH through Heterostructure Engineering to Realize High-Efficiency Electrocatalytic Formate and Hydrogen Co-Production.

An electrocatalytic methanol oxidation reaction (MOR) is proposed to replace oxygen evolution reaction (OER) in water electrolysis owing to the favorable thermodynamics of MOR than OER. However, there is still a competition between the MOR and the OER when the applied potential is in the conventional OER zone. How to inhibit OER while maintaining efficient MOR is an open and challenging question, and there are few reports focusing on this thus far. Herein, by taking NiFe layered double hydroxide (LDH) as a model catalyst due to its intrinsically high catalytic activity for the OER, the perspective of inhibiting OER is shown and thus promoting MOR through a heterogenous engineering of NiFe-LDH. The engineered heterostructure comprising NiFe-LDH and in situ formed NiFe-hexylaminobenzene (NiFe-HAB) coordination polymer exhibits outstanding electrocatalytic capability for methanol oxidation to formic acid (e.g., the Faradaic efficiencies (FEs) of formate product are close to 100% at various current densities, all of which are much larger than those (53-65%) on unmodified NiFe-LDH). Mechanism studies unlock the modification of NiFe-HAB passivates the OER activity of NiFe-LDH through tailoring the free energies for element reaction steps of the OER and increasing the free energy of the rate-determining step, consequently leading to efficient MOR.

MnO–Co@Pt nanowires encapsulated in N-doped porous carbon derived from MOFs for efficient electrocatalytic methanol oxidation reaction

Schematic illustration for the preparation of the MnO–Co@Pt NPC.

Nickel-organic frameworks as highly efficient catalyst for electrochemical conversion of CH3OH into formic acid

To improve the reaction rate and the yield of high value-added product (formic acid) of electrocatalytic methanol oxidation reaction (MOR), the development of high-performance electrocatalyst is essential. In this work, novel nickel-organic framework nanosheets comprising Ni2+ and an organic ligand of hexamethylenetetramine (Ni-MOFs-t, where t is the solvothermal temperature) are synthesized by a facile one-pot solvothermal method. By structural regulation of Ni-DMAP-t, the self-supported Ni-MOFs-120 nanosheets on Ni foam (Ni-MOFs-120/NF) exhibits high electrocatalytic activity toward MOR with a low potential of 1.44 V (vs RHE) at a current density of 100 mA cm−2. Electrochemical measurement has also demonstrated that the Ni-MOFs-120/NF possesses superior stability for MOR. Particularly, the selectively conversion of methanol to formic acid was achieved under the catalysis of Ni-MOFs-120/NF. This work offers a new high-performance electrocatalytic material for the conversion of methanol to high value-added formic aci

Platinum supported on hydroxyl-grafted poly (3,4-ethylenedioxythiophene)-modified RuCo, N-tridoped bamboo-like carbon nanotubes for direct methanol fuel cell

The development of highly active and efficient heterogeneous catalytic oxidation system has become an attractive research field. In this paper, a catalyst (RuCo/N-CNT@PEDOT-OH/Pt) from platinum nanoparticles (Pt NPs) supported on hydroxyl-grafted poly(3,4-ethylenedioxythiophene) (PEDOT–OH)-modified RuCo, N-tridoped bamboo-like carbon nanotubes (RuCo/N-CNT) are used for direct methanol fuel cell (DMFC). The electrocatalytic activity of RuCo/N-CNT@PEDOT-OH/Pt is systematically compared with RuCo/N-CNT/Pt (Pt NPs supported on RuCo/N-CNT without PEDOT-OH) in the methanol oxidation reaction (MOR). The growth mechanism of carbon nanotubes and the role of heteroatom doping in the electrocatalytic process is explored. The catalysts show excellent electrocatalytic performance with high stability for MOR. It is found that the mass activity (MA) of the RuCo/N-CNT@PEDOT-OH/Pt (1961.3 mA mg−1Pt) for MOR was higher than that of RuCo/N-CNT/Pt (1470.1 mA mg−1Pt) and the commercial Pt/C catalysts (281.0 mA mg−1Pt), indicating the positive effect of the PEDOT-OH in the electrocatalytic MOR. In addition, density functional theory (DFT) calculations verify the possible mechanism pathways of the obtained RuCo/N-CNT@PEDOT-OH/Pt catalyst. This presented catalyst offers new inspiration for designing efficient electrocatalysts for methanol oxidation.

High-performance methanol electrolysis towards energy-saving hydrogen production: Using Cu2O-Cu decorated Ni2P nanoarray as bifunctional monolithic catalyst

Electrocatalytic methanol oxidation reaction (MOR) is a promising alternative approach to oxygen evolution reaction for efficient hydrogen production. However, developing highly efficient and cost-effective MOR catalysts, coupled with the cathodic hydrogen evolution reaction, is still a challenge. Herein, we used a Ni2P nanosheet array with Cu2O-Cu dendrites on nickel foam (Cu2O-Cu@Ni2P/NF) as an efficient and stable electrocatalyst for MOR, which attained a low potential of 1.41 V at 100 mA cm−2 and a small Tafel slope of 44.99 mV dec–1 with excellent stability for at least 24 h in 1.0 M KOH solution with 1.0 M methanol. In situ Raman spectroscopy reveals that Cu2O-Cu promotes the generation of the β-NiOOH active phase, and converts to Cu(II)O under the electrolysis conditions. Furthermore, the methanol electrolysis cell utilizing Cu2O-Cu@Ni2P/NF as both the cathode and anode delivered a current density of 10 mA cm−2 at a low cell voltage of 1.40 V, and the cell voltage decreased by 210 mV at a current density of 100 mA cm−2 compared to water electrolysis. This work provides a new strategy to design the promising Ni-based phosphide as a bifunctional electrocatalyst in methanol electrolysis, enabling energy-saving H2 production.

One-Pot Synthesis of Pt Nanobowls Assembled from Ultrafine Nanoparticles for Methanol Oxidation Reaction.

Simultaneously engineering a bowl-like and ultrafine nano-size structure offers an attractive route to not only increase the utilization efficiency of noble metals, the specific surface areas and the availability of active sites, but also boost the structural robustness and long-term stability. However, a great challenge remains in terms of the methods of synthesis. Herein, we report a facile one-pot hydrothermal method for the preparation of hollow porous Pt nanobowls (NBs) assembled from ultrafine particles. N,N′-methylenebisacrylamide (MBAA) acts as a structure-directing agent that forms a self-template with Pt ions and drives the nucleation and assembly of Pt metals, resulting in the fabrication of Pt NBs from ultrafine particles. By virtue of their unique structure and morphology, the optimized Pt NBs exhibited enhanced electrocatalytic methanol oxidation reaction (MOR) activity with 3.1-fold greater mass activity and 2.6-fold greater specific activities compared with those of commercial Pt black catalysts, as well as excellent stability and anti-poisoning ability.

Unusual Role of the Surfactant in the Self-Assembly of Pt Alloy in Ordered Mesoporous Carbon: Tuning the Nanocluster Size

In the one-step self-assembly synthesis of metallic nanocrystals in ordered mesoporous carbon (OMC), the surfactant functionalizes well as the structure directing agent and mesopore template. Interestingly, this work demonstrates another unusual role the surfactant plays: tuning the size of the nanocrystals. Our investigation shows that the decreasing molecular weight of the PS segment of PEO-b-PS leads to sequentially reduced PtRu particle sizes of 4.4, 3.9, and 2.9 nm, while F127 which has a distinctly smaller hydrophobic PO domain with a bending structure in the micelles successfully results in sub-2 nm PtM (M = Ru, Ir, Rh, Pd) nanoclusters in OMC. This well indicates that the nanocluster size is largely decided by the volume of the hydrophobic segment of the surfactant to which the metallic precursor is linked. The smaller the volume, the fewer the precursor molecules are adsorbed, and the smaller the alloy nanoclusters. In the electrocatalytic methanol oxidation reaction, the mass activity of PtRu-1.6/OMC with 1.6 nm PtRu clusters at 0.87 V reaches 1.07 A mgPt-1, which is 2.9 times that of commercial PtRu/C with an average alloy size of 2.7 nm. In principle, a wide range of ultrafine metallic clusters embedded in OMC can be prepared via this route for various applications.