Electrocatalytic Activity For Methanol Oxidation Research Articles

Led-induced deposition of Pt and Au NPs on carbon fibers: Developing a novel strategy for facile fabrication of electrocatalysts for enhanced methanol electrooxidation

In addressing the imperative of aligning materials science with sustainable development, our study introduces an innovative method for the simultaneous deposition of Pt and Au nanoparticles onto a carbon support. This research represents the pioneering application of the photodeposition process for synthesizing bimetallic nanoparticles on a carbon matrix. The comprehensive characterization of the resulting nanostructures involves various techniques, including field X-ray diffraction (XRD), scanning and transmission electron microscopy (SEM and TEM), atomic force microscopy (AFM), energy-dispersive X-ray analysis (EDX), inductively coupled plasma atomic emission spectroscopy (ICP-OES), X-ray photoelectron spectroscopy (XPS), and cyclic voltammetric techniques. Our findings reveal that the photodeposition method produces a homogeneous AuPt nanostructure, demonstrating superior electrocatalytic activity in methanol oxidation compared to the monometallic carbon fiber_Pt (CF_Pt) catalyst. These results emphasize the effectiveness of our novel approach in fabricating electrocatalysts with exceptional performance in methanol oxidation reactions.

Formation of Pt-NiO/rGO triphasic junction with significantly enhanced electrocatalytic activity for methanol oxidation

Pt-based nanocomposites such as Pt- metal oxide framework have been widely used as electro catalysts for direct methanol fuel cell (DMFC) due to their significant catalytic activity and stability. In this study, Pt-NiO encapsulated with reduced graphene oxide (rGO) nanosheet is prepared by making a thin film of GO over deposited Pt-NiO on Indium tin oxide support, followed by facile electrochemical reduction technique. As-synthesized materials are characterized by X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, and transmission electron microscopy. The electrocatalytic performance is investigated by cyclic voltammetry (CV), chronoamperometry and impedance spectroscopy. These results indicate that Pt-NiO/rGO ternary phase catalyst junction exhibits significant CV peak current density (669 mA mg−1 of Pt) which is 2.9 and 1.7 times higher than that of fabricated Pt-NiO and commercial Pt(10 mass% )-XC72 respectively. The electrode also possesses excellent stable catalytic activity than Pt-NiO. The charge transfer conductance of Pt-NiO based electrode is improved 17 times and the electrochemical surface area is increased by ca. 2 times by incorporation of overhead rGO nanosheet. These results imply that Pt-NiO/rGO nanocomposite could be a better electrocatalyst for DMFCs application.

Highly Dispersed PdNi Nanoparticles on an Oxygen-Functionalized Activated Carbon with Extraordinary Electrocatalytic Activity for Methanol Oxidation

Highly Dispersed PdNi Nanoparticles on an Oxygen-Functionalized Activated Carbon with Extraordinary Electrocatalytic Activity for Methanol Oxidation

One-step production of Pt–CeO2/N-CNTs electrocatalysts with high catalytic performance toward methanol oxidation

Nitrogen-doped carbon nanotubes (N-CNTs) prepared by carbonization of polypyrrole nanotubes (PPy-NTs) are used as supports. Pt–CeO2/N-CNTs electrocatalysts are successfully prepared by in-situ growth of Pt and CeO2 nanoparticles (NPs) via a one-step coupling method of co-deposition and ethylene glycol reduction. Through structural characterization and electrochemical tests of the prepared electrocatalysts, the effects of preparation conditions on the structure of the electrocatalysts and their electrocatalytic activity for methanol oxidation were systematically investigated. The results verify that the Pt–CeO2/N-CNTs electrocatalysts were prepared using N-CNTs calcined at 700 °C as a support and 15 mM alkali concentration. They have the largest electrochemical active area and methanol oxidation mass activity of 85 m2 g−1(Pt) and 722 A g−1(Pt), respectively. Furthermore, the electrochemical stability and anti-CO poisoning performance of the electrocatalysts are significantly better than those of the commercial Pt/C electrocatalysts. The highly-dispersed Pt and CeO2 in Pt–CeO2/N-CNTs, a large number of N sites, and the synergistic action of Pt, CeO2, and N-CNTs result in a catalyst with excellent electrocatalytic activity, stability, and resistance to CO poisoning. The support structure and the dispersion of Pt and CeO2 can be controlled by changing the preparation conditions, which provides a basis for the industrial application of direct methanol fuel cells.

Pt nanoparticles in polyelectrolyte multilayers: Polymer effects on the electrocatalytic activity for methanol oxidation

The layer-by-layer (LbL) self-assembly technique is a simple and versatile tool for the controlled chemical conversion of metal ions into nanoparticles. In this work, we prepared LbL thin films containing Pt nanoparticles electroactive towards electro-oxidation of methanol by a two-step process, involving the exchange of different Pt precursor ions into the film, followed by their chemical reduction. We addressed the influence of the Pt precursor (Pt(NH3)42+ and PtCl62−) and polyelectrolyte-pairs (poly(diallyldimethylammonium chloride) (PDDA)/Nafion and poly(allylamine hydrochloride) (PAH)/poly(acrylic acid) (PAA)) on the properties and electrocatalytic activity of the nanoparticles. NPs synthesized from Pt(NH3)42+ outperformed those growth from PtCl62−, the precursor used in previous works to prepared Pt NPs within LbL films. The combination of Pt(NH3)42+ and PDDA/Nafion films produced the best electrocatalytical performance with a specific activity of 0.8 mA.cm−2Pt. By varying the number of exchange/reduction cycles (n) between 1 and 5, a marked increase in the catalytic activity was observed for the first 2 cycles, followed by a saturation regime. The peak potential of the Pt/Pt oxide peak also increases in the first cycles and approaches a constant value close to that of a bulk Pt electrode coated with PDDA/Nafion. These behaviors are explained in terms of a strong polymer-Pt surface interaction that decreases with increasing n and stabilizes for n > 2.

Vesicular AuPd alloy nanowires for enhanced electrocatalytic activity

Developing excellent fuel cells requires complex design and precise tuning of catalyst structure and composition. This paper presents a simple approach to fabricate AuPd vesicular nanowires (VNWs) with controlled composition. The method uses homogeneous Te nanowires (NWs) as templates and reducing agents in the replacement reaction and NaClO as etching agent. Bimetallic synergism and rich catalytic sites in the vesicular nanowires give AuPd catalysts the excellent electrocatalytic performance for methanol oxidation. In particular, the Au28Pd71 VNWs showed the highest electrocatalytic activity for methanol oxidation, and its highest mass current density was1.278 A mg−1, which was 1.22 and 1.65 times that of Pt VNWs and commercial Pt/C, separately. Furthermore, Au28Pd71 VNWs exhibited good stability after 2000 cycles, maintaining an initial mass current density of 85.2%. As the optimal component ratio, Au28Pd71 exhibited superior electrocatalytic performance for methanol oxidation. This discovery demonstrated a new approach for the programming and fabrication of senior methanol fuel cells electrocatalysts.

Methyl orange-modified Au nanoparticles supported on multiwalled carbon nanotubes as an electrocatalyst for methanol oxidation

The most stable metal-gold (Au) is not usually used as a catalyst component. To explore the catalytic activity of Au, Au colloidal nanoparticles were synthesized by a photochemical method and modified by methyl orange (MO) into modified Au colloidal nanoparticles solution (Au-MO). Then, Au-MO/multiwalled carbon nanotubes (Au-MO/MWCNTs) catalysts were obtained by supporting the Au-MO on the MWCNTs. The structure characterization revealed that MO attracts the electrons of Au, and electron transfer occurs from the Au nanoparticles to MO in the Au-MO/MWCNTs catalyst. Electrochemical measurements demonstrated that Au-MO/MWCNTs have a distinctly higher electrocatalytic activity for methanol oxidation than that of the Au/MWCNT catalyst. It was found that the improved electrocatalytic activity of the Au-MO/MWCNTs is derived from the electron transfer from the Au nanoparticles to MO.

Directing Energy Flow in Core-Shell Nanostructures for Efficient Plasmon-Enhanced Electrocatalysis.

Conjugating plasmonic metals with catalytically active materials with controlled configurations can harness their light energy harvesting ability in catalysis. Herein, we present a well-defined core-shell nanostructure composed of an octahedral Au nanocrystal core and a PdPt alloy shell as a bifunctional energy conversion platform for plasmon-enhanced electrocatalysis. The prepared Au@PdPt core-shell nanostructures exhibited significant enhancements in electrocatalytic activity for methanol oxidation and oxygen reduction reactions under visible-light irradiation. Our experimental and computational studies revealed that the electronic hybridization of Pd and Pt allows the alloy material to have a large imaginary dielectric function, which can efficiently induce the shell-biased distribution of plasmon energy upon illumination and, hence, its relaxation at the catalytically active region to promote electrocatalysis.

Surface Spin Enhanced High Stable NiCo2 S4 for Energy-Saving Production of H2 from Water/Methanol Coelectrolysis at High Current Density.

Nickel based materials are promising electrocatalysts to produce hydrogen from water in alkaline media. However, the stability is of great challenge, limiting its practical material functions. Herein, a new technique for electro-deposition flower-like NiCo2 S4 nanosheets on carbon-cloth (CC@NiCo2 S4 ) is proposed for energy-saving production of H2 from water/methanol coelectrolysis at high current density by constructing array architectures and regulating surface magnetism. The optimized and fine-tuned magnetism on the surface of the electrochemical in situ grown CC@NiCo2 S4 nanosheet array result in (0 1 -1) surface universally exposed, high catalytic activity for methanol electrooxidation, and long-term stability at high current density. X-ray photoelectron spectroscopy in combination of density functional theory calculations confirm the valence electron states and spin of d electrons for the surface of NiCo2 S4 , which enhance the surface stability of catalysts. This technology may be utilized to alter the surface magnetism and increase the stability of Ni-based electrocatalytic materials in general.

Advanced LDH-MOF derived bimetallic NiCoP electrocatalyst for methanol oxidation reaction

Design and synthesis of hierarchical electrocatalysts with abundant active sites is an effective approach to improve electrocatalytic activity for methanol oxidation. Hierarchical LDH-MOF derived NiCo-bimetallic phosphide (NiCo-MOF-P) has been tested for methanol oxidation reaction (MOR) in alkaline solution. Electrodeposited NiCo-LDH gives extra chemical and structural stability for MOF to avoid accumulation. Obtained LDH-MOF hybrid composite was further surface functionalized by selective phosphorization to enhance electrocatalytic activity by generating more active sites. The NiCo-MOF-P electrocatalyst showed current density 170 mA cm-2 at scan rate of 10 mV s-1 with remarkable long term stability in 0.5 M methanol in 1 M KOH at 1.54 V. The high electrocatalytic activity of NiCo-MOF-P electrocatalyst towards methanol oxidation is mainly associated with synergistic effect of bimetallic element (Ni and Co), high surface area and facilitated charge-transfer due to binder free growth on Ni foam.

Surface hydroxy functionalized Pt/g-C3N4-CNS for highly efficient methanol electrocatalytic oxidation

In this paper, CN(g-C3N4) and CNS(carbon nanosheets) were assembled by hydrothermal method to synthesize CN-CNS(g-C3N4-carbon nanosheets) composite carriers, then CN-CNS-x(g-C3N4-carbon nanosheets-mass of KOH(g)) carriers were prepared with KOH heat treatment. Finally, Pt nanoparticles were loaded onto the surface of CN-CNS-x carriers using NaBH4. The effect of the functionalized CN-CNS-x carriers on the catalytic performance of Pt/CN-CNS catalysts was investigated by electrochemical tests. It was demonstrated that Pt/CN-CNS-0.04(g-C3N4-carbon nanosheets-0.04g KOH) had the best electrocatalytic activity for methanol oxidation, with a specific activity of 123.58 mA/cm2 and the best stability among all catalysts. Through a series of characterization, it was found that the KOH treated CN-CNS carrier has a larger specific surface area, and the increased hydroxyl group on the carrier surface can interact with the Pt species, which helps the anchoring of Pt nanoparticles. Simultaneously, the hydroxyl groups on the carrier surface can accelerate the oxidation of CO, thus obtaining better electrocatalytic performance.

Electrochemically-Assisted Synthesis of Platinum Nanoparticles Using Gas-Diffusion Electrocrystallization (GDEx) and Their Electrocatalytic Activity for Methanol Oxidation

In recent years, interest in using unsupported catalysts, especially Pt-based nanomaterials, has resurged in direct methanol fuel cells (DMFC). Unsupported catalysts eliminate the problems related to the corrosion of carbon catalyst supports, thus improving the long-term stability of DMFC. In addition, the design of catalyst synthesis protocols to tailor nanostructured materials with high surface area and catalytic activity improves catalyst performance.1 Consequently, we recently reported a method for the synthesis of platinum group metal (PGM, i.e., Pt, Pd, Rh) nanoparticles (NPs), using a process called Gas Diffusion Electrocrystallization (GDEx) (Fig. 1a).2 The simultaneous electrochemical reduction of CO2 and water occurs at the triple-phase boundary of uncatalyzed gas-diffusion electrodes, producing H2 and CO. Both gases, but especially H2, are reducing agents for water-soluble noble metal ions leading to the formation of small metal nanoclusters. CO can also act as a capping agent. Furthermore, the presence of CO2 stabilizes the pH, avoiding the formation of metal (hydr)oxides.In this work, we used the GDEx process to synthesize unsupported Pt NPs using polyvinyl pyrrolidone (PVP, 55000 Mw) as a stabilizer and evaluated their electrocatalytic activity for methanol oxidation. The synthesis was performed at -30 mA cm-2, using 3.0 mM Pt4+ (as H2PtCl4) as metal precursor and different concentrations of PVP (i.e., 0.0, 0.01, 0.1 and 1.0 g L-1). We chose low concentrations of stabilizer to facilitate its removal after synthesis, as clean surface catalysts are required for electrocatalytic applications. The size distribution of the Pt NPs, measured using Scanning Electron Microscopy (SEM), was 64 ± 22, 60 ± 22, 42 ± 18, and 38 ± 12 nm for PVP 0.0, PVP 0.01, PVP 0.1, and PVP 1.0, respectively. For comparison, the reduction of 3.0 mM Pt4+ using 1.0 g L-1 PVP with only H2 (either electrogenerated or bubbled) produced bigger and much more polydisperse particles (100 nm–1000 nm), highlighting the importance of the GDEx process and the presence of CO to synthesize small NPs using low concentrations of stabilizer. Furthermore, Transmission Electron Microscopy (TEM) images (Fig. 1b) revealed that the NPs are nanoclusters of single crystals of 2 nm–4 nm in diameter.The synthesized Pt NPs were cleaned using NaOH,3 and their electrocatalytic activity was evaluated in acidic media. The CV curves of Pt NPs in 0.5 M H2SO4 are shown in Fig. 1c. All catalysts showed hydrogen adsorption-desorption peaks from -0.2 to 0.1 VAg/AgCl. The calculated electrochemical surface area (ECSA), obtained by integrating the charge in the hydrogen adsorption-desorption region, was 7.6 ± 0.7, 14.1 ± 1.2, 33.6 ± 1.2, and 30.3 ± 1.0 m2 g-1 Pt for PVP 0.0, PVP 0.01, PVP 0.1 and PVP 1.0 respectively. The MeOH electro-oxidation experiments were performed in 0.5 M H2SO4 containing 1.0 M MeOH, and the CV curves are shown in Fig. 1d. The forward anodic peak (If) at about 0.7 VAg/AgCl corresponds to MeOH oxidation, while the backward anodic peak (Ib) at about 0.5 VAg/AgCl corresponds to the oxidation of the incompletely oxidized carbonaceous species formed in the forward sweep. The mass activity (MA), defined by the forward peak current density per unit of catalyst loading, was 71 ± 2, 136 ± 7, 463 ± 28, and 341 ± 25 mA mg-1 Pt for PVP 0.0, PVP 0.01, PVP 0.1, and PVP 1.0 g L-1, respectively. Hence, the MA scale with the ECSA . Besides, ECSA (and hence MA) increases when the PVP concentration during synthesis increases. However, this trend is not followed for a PVP concentration of 1.0 g L-1. Even though all catalysts were cleaned using the same protocol, residual PVP might still be left on the surface of Pt NPs synthesized using 1.0 g L-1 PVP, lowering their electrocatalytic activity.Overall, the GDEx process was a useful tool for synthesizing unsupported Pt NPs using low concentrations of stabilizer and with high electrocatalytic activity. This project has received funding from the European Union's Horizon 2020 Research and Innovation program under Grant Agreements n° 730224 (PLATIRUS) and n° 958302 (PEACOC) 1. E. Antolini, J. Perez, J. Mat. Sci, 2011, 46, 4435–4457.2. X. Dominguez-Benetton, O. Martinez-Mora, J. Fransaer, EP21165681, 2021.3. A. Zalineeva, S. Baranton, C. Coutanceau, G. Jerkiewicz, Langmuir, 2015, 31, 1605–1609. Figure 1

(Digital Presentation) Facile Fabrication of Graphene Quantum Dot- Doped Polyaniline Embedded Cu Metal-Organic Frameworks Composite Electrode As Improved Anode Electrocatalyst for Methanol Oxidation

Nonrenewable energy sources accounted for roughly 80% of total energy consumption [1]. Solar energy, wind energy, geothermal energy, hydropower, and fuel cells (FCs) have all recently been described as renewable energy sources. In commercial uses, renewable energy has experienced meteorological and logistical obstacles. Because of advantages such as simple fabrication/operation conditions, eco-friendly, high energy conversion efficiency, and long-term durability, FCs technologies are considered one of the most important renewable energy sources for many applications such as portable devices, cars, and electricity plants [2–5]. Methanol can be utilized in direct methanol fuel cells (DMFC) to produce clean energy that can be used in smart electronic gadgets or small automobiles in this regard [6]. However, before DMFC can be used commercially, the slow oxidation kinetics and catalyst toxicity [7] must be resolved. Therefore, the development of direct methanol fuel cells (DMFCs) is one of the most promising technologies for the applications of these devices in stationary power supplies and electric vehicles [8]. Apart from the future of mobile devices such as mobile chargers, phones, computers, and many other applications, this energy is environmentally benign because no gases are emitted and the waste is simply clean water. The biggest issue that this technique may encounter is its high cost due to the usage of noble metal catalysts (platinum (Pt) and ruthenium (Ru)) [9]. Methanol is oxidized via a multi-electron process and several products and/or intermediates can be formed, depending on the electrolyte and the nature of the electrode. Electrode materials are important parameters in the electrochemical oxidation of methanol, where high efficient electrocatalysts are needed. Several metal oxides such as Fe2O3, CeO2, MoOx, Co3O4, NiO, and CuO has been used in various applications, such as catalysis, water splitting photocatalysis, solar cells and gas sensing, besides their uses to enhance the electrocatalytic activity for methanol oxidation [10-11].This paper describes the preparation of graphene quantum dot-doped polyaniline embedded copper metal-organic frameworks composite catalysts for investigating methanol oxidation in alkaline solutions. The electrode surface was characterized by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), and electrochemical impedance spectroscopy (EIS). After physicochemical characterizations of graphene quantum dot-doped polyaniline embedded copper metal-organic frameworks composite modified carbon ceramic electrode (Cu- MOF/GQDs-PAN/CCE), its electrocatalytic and stability characterizations toward methanol oxidation in alkaline media were investigated in detail by cyclic voltammetry and chronoamperometry. Results showed that, the electrocatalytic activity of the Cu- MOF/GQDs-PAN/CCE electrode is much higher than those of unmodified electrode under similar experimental conditions, showing the possibility of attaining good electrocatalytic anodes for fuel cells. Kinetic parameters such as the electron transfer coefficient (α) and the number of electrons involved in the rate determining step (nα) for the oxidation of methanol were determined utilizing cyclic voltammetry (CV). Keywords: Graphene quantum dot, Polyaniline, Metal-organic frameworks, electrocatalyst, MethanolReferences[1] S.K. Kamarudin, F. Ahmad, W.R.W. Daud, Overview on application of direct methanol fuel cell (DMFC) for portable electronic devices, Int. J. Hydrog. Energy 34 (2009) 6902–6916.[2] L. Carrette, K.A. Friedrich, U. Stimming, Fuel cells: principles, types, fuels and applications, ChemPhysChem 1 (2000) 162–193.[3] A.B. Stambouli, Fuel cells: The expectations for an environmental-friendly and sustainable source of energy, Renew. Sustain. Energy Rev. 15 (9) (2011) 4507– 4520.[4] P. Joghee, J.N. Malik, S. Pylypenko, R. O’Hayre, A review on direct methanol fuel cells – In the perspective of energy and sustainability, MRS Energy Sustain. 2 (2015), https://doi.org/10.1557/mre.2015.4.[5] D. Hassen, M.A. Shenashen, S.A. El-Safty, M.M. Selim, H. Isago, A. Elmarakbi, H. Yamaguchi, Nitrogen-doped carbon-embedded TiO2 nanofibers as promising oxygen reduction reaction electrocatalysts, J. Power Sources 330 (2016) 292– 303.[6] M. Mansor, S.N. Timmiati, K.L. Lim, W.Y. Wong, S.K. Kamarudin, N.H. Nazirah Kamarudin, Recent progress of anode catalysts and their support materials for methanol electrooxidation reaction, Int. J. Hydrogen Energy 44 (29) (2019) 14744–14769, https://doi.org/10.1016/j.ijhydene.2019.04.100.[7] Z. Mousavi, A. Benvidi, S. Jahanbani, M. Mazloum-Ardakani, R. Vafazadeh, H. R. Zare, Investigation of electrochemical oxidation of methanol at a carbon paste electrode modified with Ni(II)-BS complex and reduced graphene oxide nano sheets, Electroanalysis 28 (12) (2016) 2985–2992, https://doi.org/10.1002/ elan.201501183.[8] S. Wasmus, A. Küver, Methanol oxidation and direct methanol fuel cells: a selective review, J. Electroanal. Chem. 461 (1-2) (1999) 14–31.[9] M. Liu, R. Zhang, W. Chen, Graphene-Supported Nanoelectrocatalysts for Fuel Cells: Synthesis, Properties, and Applications, Chem. Rev. 114 (2014) 5117– 5160.[10] N. Spinner, W.E. Mustain, Electrochim. Acta 56 (2011) 5656.[11] M.S. Risbud, S. Baxter, M. Skyllas-Kazacos, Open Fuels Energy Sci. J. 5 (2012) 9.

Facile Preparation of Porous Carbon Flake-Supported Nickel Nanoplates as Effective Catalysts for Methanol Electrooxidation

Herein, we report a facile and efficient method for fabricating porous carbon flakes (PCFs)-supported nickel nanoplates (Ni NPs) as electrocatalysts for methanol oxidation in alkaline media. The catalyst was fabricated in one step using molten salt synthesis. Various techniques were used to characterize the morphology and composition of the Ni NPs@PCFs catalyst, and these revealed that the Ni NPs were dispersed finely across the PCFs with a highly crystalline structure. The Ni NPs@PCFs catalyst demonstrated high electrocatalytic activity for methanol oxidation (121 mA/cm2 vs. Ag/AgCl), and it had an onset potential of 0.35 V. It also exhibited high stability in an alkaline electrolyte for the duration of the experiment (up to 2000 s).

Defect-rich PtPdCu flower-like nanoframes with enhanced electrocatalytic activity for methanol oxidation

Nanoframe structures with rich defects are desirable in the field of catalysis, whereas the precise synthesis of them remains challenging. In this study, the defect-rich PtPdCu flower-like nanoframes have been successfully synthesized by oxidative etching of pre-prepared PdCu@Pt core-shell nanoflowers. According to the experiment results, the formation of PdCu@Pt core-shell nanoflowers plays a decisive role in synthesizing PtPdCu flower-like nanoframes. Due to its novel structures with rich defects and the synergistic effect between Pd, Cu and Pt, PtPdCu flower-like nanoframes exhibit enhanced catalytic activity. In special, the mass activity of PtPdCu flower-like nanoframes is 2.0 and 7.0 times as large as that of PdCu@Pt core-shell nanoflowers and Pt black for methanol oxidation reaction (MOR) in acidic medium, respectively. Furthermore, PtPdCu flower-like nanoframes present exceptionally stability even after the long-term accelerating test.

Boosting the Multifunctional Properties of MnCo2O4‐MnCo2S4 Heterostructure for Portable All‐Solid‐State Symmetric Supercapacitor, Methanol Oxidation and Hydrogen Evolution Reaction

AbstractThis article reports on the preparation of MnCo2O4‐MnCo2S4 heterostructure by facile solvothermal route towards the application of supercapacitor‐based energy storage as well as methanol electro‐oxidation and hydrogen evolution reaction. Dunn's methodology has been adopted for the evaluation of charge storage by capacitive process and diffusion‐controlled process and the quantification of the charge stored at exterior surface and interior surface was done by Trasatti's approach. The prepared heterostructure was utilized as an electrode in the symmetric solid‐state device based on Na2MoO4 redox electrolyte and exhibits remarkable performance in terms of specific capacity, cyclic performance, energy, and power density. The fabricated device exhibits a specific capacity of 417 C g−1 at a specific current of 1 A g−1, and shows retention of 84.2 % after 5000 galvanostatic charge‐discharge cycles, and specific energy of 81 Wh kg−1 at a specific power of 700 W kg−1. Series combination of two solid‐state symmetric devices was capable to light up a red LED for 30 min and an array of 22 red LEDs for 8 min. The heterostructure shows remarkable catalytic activity for methanol electrooxidation by increasing catalytic current almost four times in 2 M methanol and 1 M KOH electrolyte at 0.6 V and also lowering the onset potential as 0.331 V. The excellent electrocatalytic activity of MnCo2O4‐MnCo2S4 heterostructure towards the hydrogen evolution reaction was observed by showing the requirement of low overpotential (‐175 mV) to reach the current density of −10 mA cm−2 along with small Tafel slope (102 mV dec−1). The electrode material revealed enormous stability by providing a constant current over 20 h in chronoamperometry measurements. The better electrochemical performance of microspheres could be attributed to large surface area which promotes the catalytic reactions at the large number of active sites.

Tailoring the Metallic and Oxide Sites of Pd/C and Ni/C Catalysts for Optimum Hydrogen Oxidation Reaction (HOR) and Durability in Alkaline Media

In recent years, Pd- and Ni-based, or Pd-Ni alloys catalysts for HOR in alkaline electrolytes obtained increasing attention due to their higher durability than Pt-based catalysts. [1-3] However, to prevent passivation in high pH media and maintain active metal/oxide sites, it is necessary to protect the surface of Pd and Ni. It is well documented that different types of carbon cover layers surrounding Ni particles, such as graphite or carbon nanotube, can be beneficial for several applications, e.g. hydrogenation, dehydrogenation, methanol oxidation [4-6], and HOR. Gao et al. reported different degree of graphite coverage-Ni particles of controlled metal/oxide ratio that can enhance the HOR activity of Ni in alkaline electrolytes [7]. In this work, we explore different carbon layer properties, morphology and thickness that cover Pd and Ni particles. Thicker cover layers lead to low HOR activity initially because of the un-balanced metal/oxide sites (the amount of metal sites is higher originally), but can be improved (activated) by voltage pulsing (0.1 - 1.23 V vs. RHE, 3 s each potential, 300 cycles) in 0.1 M KOH, 25°C, Ar gas, without agglomerating the particles (as shown in Figure 1). After full activation, protected Pd and protected Ni were compared with bare Pd and bare Ni (no protecting layers) before and after accelerated stress test (AST) in the potential range of [0.1, 1.23] V vs. RHE. IL-TEM, XRD and XPS techniques show that for protected Pd and Ni, the passivation and degradation happen much slower than for bare Pd and bare Ni (which are immediately deactivated upon AST); also, the proportion of metal or oxide sites can be tailored by different activation procedure, which renders these protected catalysts suitable for long-term alkaline HOR. Figure 1 IL-TEM of Pd C1 (Pd-capped 1) at its initial state vs. post-activation (300 cycles-Ar). Top: 200 k magnified micrographs. Bottom: 500 k magnified micrographs.[1] Lafforgue, C.; Zadick, A.; Dubau, L.; Maillard, F.; Chatenet, M. Selected Review of the Degradation of Pt and Pd-Based Carbon-Supported Electrocatalysts for Alkaline Fuel Cells: Towards Mechanisms of Degradation. Fuel Cells 2018, No. 0, 1–10.[2] Sankar, S.; Anilkumar, G. M.; Tamaki, T.; Yamaguchi, T. Binary Pd−Ni Nanoalloy Particles over Carbon Support with Superior Alkaline Formate Fuel Electrooxidation Performance. ChemCatChem 2019, 11 (19), 4731–4737.[3] Zhao, Y.; Wang, G.; Xiao, L.; Lu, J.; Zhuang, L. Hydrogen Oxidation Reaction on Pd-Ni(OH)2 Composite Electrocatalysts in an Alkaline Electrolyte. ChemistrySelect 2020, 5 (26), 7803–7807. )[4] Ortega-Domínguez, R. A.; Vargas-Villagrán, H.; Peñaloza-Orta, C.; Saavedra-Rubio, K.; Bokhimi, X.; Klimova, T. E. A Facile Method to Increase Metal Dispersion and Hydrogenation Activity of Ni/SBA-15 Catalysts. Fuel 2017, 198, 110–122.[5] Jiao, C.; Sun, L.; Xu, F.; Liu, S. S.; Zhang, J.; Jiang, X.; Yang, L. NiCo Nanoalloy Encapsulated in Graphene Layers for Improving Hydrogen Storage Properties of LiAlH4. Sci. Rep. 2016, 6 (January), 4–11.[6] Tong, X.; Qin, Y.; Guo, X.; Moutanabbir, O.; Ao, X.; Pippel, E.; Zhang, L.; Knez, M. Enhanced Catalytic Activity for Methanol Electro-Oxidation of Uniformly Dispersed Nickel Oxide Nanoparticles-Carbon Nanotube Hybrid Materials. Small 2012, 8 (22), 3390–3395.[7] Yang, Y.; Sun, X.; Han, G.; Liu, X.; Zhang, X.; Sun, Y.; Zhang, M.; Cao, Z.; Sun, Y. Enhanced Electrocatalytic Hydrogen Oxidation on Ni/NiO/C Derived from a Nickel-Based Metal–Organic Framework. Angew. Chemie - Int. Ed. 2019, 58 (31), 10644–10649.[8] Gao, Y.; Peng, H.; Wang, Y.; Wang, G.; Xiao, L.; Lu, J.; Zhuang, L. Improving the Antioxidation Capability of the Ni Catalyst by Carbon Shell Coating for Alkaline Hydrogen Oxidation Reaction. ACS Appl. Mater. Interfaces 2020, 12 (28), 31575–31581. Figure 1

Investigation of palladium-mesostructured silica nanoparticles (Pd-MSN) as anode electrocatalyst for alkaline direct methanol fuel cell

The commercialization of fuel cells is hindered by the high cost of noble metal electrocatalysts, such as platinum. Mesostructured silica nanoparticles (MSNs), as a novel catalyst support, are added to active palladium nanoparticles to create a Pd-MSN electrocatalyst with low Pd content to improve catalytic efficacy and decrease costs. Wet impregnation method was used to prepare catalysts that comprise palladium nanoparticles supported on MSNs (i.e. 5 wt% Pd-MSN, 10 wt% Pd-MSN, 15 wt% Pd-MSN, 20 wt% Pd-MSN and 20 wt% Pd-C) to enhance electrocatalytic activity for methanol oxidation. The structures of the catalysts were characterized by X-ray diffraction (XRD), Fourier transform infrared spectrometry (FTIR), field-emission scanning electron microscopy (FESEM), energy-dispersive X-ray (EDX) and Brunauer–Emmet–Teller (BET) surface area analysis, and their electrocatalytic performance towards methanol oxidation was investigated by cyclic voltammetry (CV) and chronoamperometry (CA). Amongst the catalysts, 20 wt% Pd-MSN has the highest electrocatalytic activity (14.3 mA cm−2) and stability (3600 s) for methanol oxidation in alkaline medium at the constant potential of −0.2 V. This result indicates that 20 wt% Pd-MSN may be a promising anode material for direct methanol fuel cells. The improved electrocatalytic activity and stability of the electrocatalyst are attributed to the high specific surface area of MSN and the effective surface structure of Pd nanoparticles. Furthermore, MSN increases catalyst dispersion by producing new active sites, which results in the promotion of Pd utilization.

Preparation of Pd/ZnO/Ni hierarchical porous array film with enhanced electrocatalytic activity for methanol oxidation

In this study, we successfully synthesized a Pd/ZnO/Ni hierarchical porous array-film catalyst by electrodeposition and magnetron sputtering with the assistance of the monodisperse colloidal sphere template. Structural characterisation indicated that a layer of Pd nanoparticles was uniformly grown on the ZnO/Ni ordered bowl-like micro/nano array film. Electrochemical measurements in alkaline solution demonstrated that the as-grown array film had outstanding electrocatalytic activity for methanol oxidation. The specific activity of the Pd/ZnO/Ni porous array film was up to 130.1 mA cm−2. The corresponding mass activity (812.7 mA mg−1) was 6 times higher than that of commercial Pd/C catalyst (134.8 mA mg−1), and the stability was also much better than the commercial one. These excellent electrochemical properties can be attributed to the unique hierarchical porous structure, which offers a high specific surface area for the methanol reaction, and ZnO intermediate layer, which effectively removes the poisoning species from the Pd sites through the strong oxidative hydroxyl radicals.

Highly controlled synthesis of nanoprickly nickel@nickel oxide formed on carbon black/reduced graphene oxide nanosheets: Charge-storage performance and electrocatalytic activity for methanol oxidation

Supercapacitive performance and electrocatalytic activity of the nickel@nickel oxide core@shells (Ni@NiO), formed with different composition, structure, and morphology via electroless deposition on the surface of carbon black/reduced graphene oxide nanosheets (CB/RGONs) in the presence of citrate ion are reported here. The conditions are controlled and the synthesis is carried out systematically via three different routes: (a) in the absence of CB and citrate ion, (b) just in the presence of CB, and (c) in the presence of both CB and citrate ion. Then, the synthesized composites were transferred onto the GC electrodes, leading to (a) GC-RGONs-PNi@NiO(Particles), (b) GC-RGONs-HENi@NiO(Hedgehog), and (c) GC-CB/RGONs-NPNi@NiO(Nanoprickly) systems, respectively. The synthesis process is followed by several surfaces and electrochemical techniques, from which the physicochemical behaviors of the prepared composites and electrode systems were determined, and the systems were characterized. Then, their activities for capacitive charge storage and electrooxidation of methanol were quantitatively studied. The composite fabricated under optimized conditions, Nanoprickly system, exhibited (i) the most efficient charge storage behavior with specific capacitance (Cs) of 2398 F g−1; and (ii) a large electrocatalytic activity for electrooxidation of methanol with peak current density of 154 A g−1 at 10 mV s−1, compared with values of 1451 & 1049 F g−1 and 72 & 58 A g−1 obtained for the composite ancestors, Hedgehog and Particle systems, respectively. The increase in the Cs and improvement in the electrocatalytic activity of the nanocomposite are attributed to the (i) crucial role of CB nanospacer, preventing graphene layers from restacking, (ii) role of RGONs, dispersing and stabilizing of Ni@NiO nanoprickly particles, and (iii) synergetic chemical coupling effect between NPNi@NiO and CB/RGONs.