Platinum-Based Catalysts on Various Carbon Supports and Conducting Polymers for Direct Methanol Fuel Cell Applications: a Review

Solid state preparation of carbon-supported Pt2Ca nanoparticles for the oxygen reduction reaction

Pt2Ca nanoparticles with a mean size diameter of 6 nm can be prepared by heating K2PtCl6, CaH2, carbon black and KCl at 400-500 °C. A mechanism study suggests that the formation of the Pt2Ca phase at moderate temperature is enabled by the fast ion transport via the vacancies in the KCl-CaH2 solid solution. The Pt2Ca nanoparticles exhibit high performance for the oxygen reduction reaction in acid due to optimal adsorption energy of the oxygen intermediate.

Green and sustainable use of macadamia nuts as support material in Pt-based direct methanol fuel cells

The successful commercialization of direct methanol fuel cells (DMFCs) is hindered by inadequate methanol oxidation activity and anode catalyst longevity. Efficient and cost-effective electrode materials are imperative in the widespread use of DMFCs. While Platinum (Pt) remains the primary component of anodic methanol oxidation reaction (MOR) electrocatalysts, its utilization alone in DMFC systems is limited due to carbon monoxide (CO) poisoning, instability, methanol crossover, and high cost. These limitations impede the economic feasibility of Pt as an electrocatalyst. Herein, we present the use of powdered activated carbon (PAC) and granular activated carbon (GAC), both sourced from macadamia nut shells (MNS), a type of biomass. These bio-based carbon materials are integrated into hybrid supports with reduced graphene oxide (rGO), aiming to enhance the performance and reduce the production cost of the Pt electrocatalyst. Electrochemical and physicochemical characterizations of the synthesized catalysts, including Pt-rGO/PAC-1:1, Pt-rGO/PAC-1:2, Pt-rGO/GAC-1:1, and Pt-rGO/GAC-1:2, were conducted. X-ray diffraction analysis revealed crystallite sizes ranging from 1.18 nm to 1.68 nm. High-resolution transmission electron microscopy (HRTEM) images with average particle sizes ranging from 1.91 nm to 2.72 nm demonstrated spherical dispersion of Pt nanoparticles with some agglomeration across all catalysts. The electrochemical active surface area (ECSA) was determined, with Pt-rGO/GAC-1:1 exhibiting the highest ECSA of 73.53 m2 g-1. Despite its high ECSA, Pt-rGO/GAC-1:1 displayed the lowest methanol oxidation reaction (MOR) current density, indicating active sites with poor catalytic efficiency. Pt-rGO/PAC-1:1 and Pt-rGO/PAC-1:2 exhibited the highest MOR current densities of 0.77 mA*cm-2 and 0.74 mA*cm-2, respectively. Moreover, Pt-rGO/PAC-1:2 and Pt-rGO/PAC-1:1 demonstrated superior electrocatalytic mass (specific) activities of 7.55 mA/mg (0.025 mA*cm-2) and 7.25 mA/mg (0.021 mA*cm-2), respectively. Chronoamperometry tests revealed Pt-rGO/PAC-1:2 and Pt-rGO/PAC-1:1 as the most stable catalysts. Additionally, they exhibited the lowest charge transfer resistances and highest MOR current densities after durability tests, highlighting their potential for DMFC applications. The synthesized Pt supported on PACs hybrids demonstrated remarkable catalytic performance, stability, and CO tolerance, highlighting their potential for enhancing DMFC efficiency.

Condensed Layer Deposition of Nanoscopic TiO2 Overlayers on High-Surface-Area Electrocatalysts

Encapsulating an electrocatalytic material with a semipermeable, nanoscopic oxide overlayer offers a promising approach to enhancing its stability, activity, and/or selectivity compared to an unencapsulated electrocatalyst. However, applying nanoscopic oxide encapsulation layers to high-surface-area electrodes such as nanoparticle-supported porous electrodes is a challenging task. This study demonstrates that the recently developed condensed layer deposition (CLD) method can be used for depositing nanoscopic (sub-10 nm thick) titanium dioxide (TiO2) overlayers onto high-surface-area platinized carbon foam electrodes. Characterization of the overlayers by transmission electron microscopy (TEM) and electron energy loss spectroscopy (EELS) showed that the films are amorphous, while X-ray photoelectron spectroscopy confirmed that they exhibit TiO2 stoichiometry. Electrodes were also characterized by hydrogen underpotential deposition (Hupd) and carbon monoxide (CO) stripping, demonstrating that the Pt electrocatalysts remain electrochemically active after encapsulation. Additionally, copper underpotential deposition (Cuupd) measurements revealed that TiO2 overlayers are effective at blocking Cu2+ from reaching the TiO2/Pt buried interface and were used to estimate that between 43 and 98% of Pt surface sites were encapsulated. Overall, this study shows that CLD is a promising approach for depositing nanoscopic protective overlayers on high-surface-area electrodes.

Electrocatalytic Oxidation of Methanol and Ethanol with 3d-Metal Based Anodic Electrocatalysts in Alkaline Media Using Carbon Based Electrode Assembly

Homogeneous electrocatalytic systems based on readily available, earth-abundant, inexpensive base metals Ni, Co, and Cr have been formulated for the electro-oxidation of alcohols (methanol and ethanol) that constitute a key half-cell component of direct alcohol fuel cells (DAFCs). Notably, excellent results were obtained for both methanol as well as ethanol electro-oxidation while operating with a half-cell assembly based on all-non-noble working and counter electrode systems consisting of glassy carbon and graphite rod, respectively. Using NaOH as the supporting electrolyte, Ni/Co/Cr metal salts and their bis(iminopyridine) complexes have been used as anodic electrocatalysts for the alcohol half-cell reactions, and among them, catalytic systems based on Co outperformed the corresponding systems based on Ni and Cr. The system comprising CoCl2.·6H2O [10 mM] + NaOH [6 M] at room temperature emerged as the best electrocatalyst for both methanol [5 M] electro-oxidation (ca. 522.5 ± 13.5 mA cm-2 at 1.4 V) and ethanol [5 M] electro-oxidation (ca. 209 ± 25 mA cm-2 at 1.34 V). It was observed that regardless of the starting alcohol, the end product is carbon dioxide, all of which gets trapped as sodium carbonate (up to 97% yield), thereby mitigating any possible hazards of greenhouse gas emission. Inferences obtained from FETEM, FESEM, and EDS analysis of both the electrolyte solution and residues deposited on the electrode surface provide evidence for the mostly homogeneous nature of the reaction mixture with the molecular catalyst being the major contributor toward the electrocatalytic activity apart from the minor role played by trace heterogeneous particles. The current cell assembly operating with non-noble working and counter electrodes utilizing a catalytic system based on an earth-abundant, base metal salt/complex that not only results in good half-cell current densities for high-energy power-source DAFCs but also generates high-value sodium carbonate offers an exciting avenue.

Catalytic Properties of Biochar as Support Material Potential for Direct Methanol Fuel Cell: A Review

With the evolution and emergence of compounding environmental problems and issues, renewable energy promises to be a sustainable future technology. One technology considered is the fuel cell, which thrives on the primary function of electrocatalytic activities. Thus this review article envisages and presents a comprehensive summary of the applications of activated carbonaceous material as supports for electrocatalysts in fuel cells. The different techniques utilized to produce these carbon materials are discussed in detail. The overview architecture and the principle of the operation of fuel cells are also addressed. Additionally, electrocatalysts and the importance of support materials, their characteristics, and the role they play in the performance of the electrocatalyst will be reviewed. Unfortunately, the carbon-support-based electrocatalyst suffers long-term instability due to corrosion. Previously, carbon black has been used as a carbon support in various fuel cells. In recent years, there has been progress in the incorporation of nanostructured carbon supports in electrocatalysts in various fuel cells; however, there is still a great deal of distance to cover for nanostructured carbon-supported electrocatalysts in fuel cells to realize full commercialization and large-scale industrial purposes due to shortcomings in electrocatalysts, which are low-cost and highly efficient. This review therefore discusses the progress of incorporation of biochar extracted from sugar cane bagasse as carbon support in electrocatalysts for direct methanol fuel cells with the intention to provide insight into the quest of producing highly efficient and low cost fuel cells.

Activated platinum in gallium-based room-temperature liquid metals for enhanced reduction reactions

Room-temperature gallium-based liquid metals (LMs) have recently attracted significant attention worldwide for application in catalysis because of their unique combination of fluidic and catalytic properties. Platinum loading in LMs is expected to enhance the catalytic performance of various reaction systems. However, Pt-loaded methods for Ga-based LMs have not yet been sufficiently developed to improve the catalytic performance and Pt utilization efficiency. In this study, a novel method for the fabrication of Pt-incorporated LMs using Pt sputter deposition (Pt(dep)-LMs) was developed. The Pt(dep)-LMs contained well-dispersed Pt flakes with diameters of 0.89 ± 0.6 μm. The catalytic activity of the Pt(dep)-LM with a Pt loading of ∼0.7 wt% was investigated using model reactions such as methylene blue (MB) reduction and hydrogen production in an acidic aqueous solution. The Pt(dep)-LMs showed a higher MB reduction rate (three times) and hydrogen production (three times) than the LM loaded with conventional Pt black (∼0.7 wt%). In contrast to the Pt(dep)-LMs, solid-based Ga with a Pt loading of ∼0.7 wt% did not catalyze the reactions. These results demonstrate that Pt activation occurred in the Pt(dep)-LMs fabricated by Pt sputtering, and that the fluidic properties of the LMs enhanced the catalytic reduction reactions. Thus, these findings highlight the superior performance of the Pt deposition method and the advantages of using Pt-LM-based catalysts.

Al-Sehemi A, Alargarsamy S, Gajendran P, Ramachandran R. Development of Different Kinds of Electrocatalyst for the Electrochemical Reduction of Carbon Dioxide Reactions: An Overview

Significant advancements have been made in the development of CO2 reduction processes for applications such as electrosynthesis, energy storage, and environmental remediation. Several materials have demonstrated great potential in achieving high activity and selectivity for the desired reduction products. Nevertheless, these advancements have primarily been limited to small-scale laboratory settings, and the considerable technical obstacles associated with large-scale CO2 reduction have not received sufficient attention. Many of the researchers have been faced with persistent challenges in the catalytic process, primarily stemming from the low Faraday efficiency, high overpotential, and low limiting current density observed in the production of the desired target product. The highlighted materials possess the capability to transform CO2 into various oxygenates, including ethanol, methanol, and formates, as well as hydrocarbons such as methane and ethane. A comprehensive summary of the recent research progress on these discussed types of electrocatalysts is provided, highlighting the detailed examination of their electrocatalytic activity enhancement strategies. This serves as a valuable reference for the development of highly efficient electrocatalysts with different orientations. This review encompasses the latest developments in catalyst materials and cell designs, presenting the leading materials utilized for the conversion of CO2 into various valuable products. Corresponding designs of cells and reactors are also included to provide a comprehensive overview of the advancements in this field.

Insights into Structural Behaviors of Thiolated and Aminated Reduced Graphene Oxide Supports to Understand Their Effect on MOR Efficiency

It is essential to develop novel catalysts with high catalytic activity, strong durability, and good stability for further application in methanol fuel cells. In this work, we present for the first time the effect of the chemical functional groups (thiol and amine) with different electron affinity in reduced graphene oxide supports on the morphology and catalytic activity of platinum nanoparticles for the methanol oxidation reaction. Hydroxyl groups on graphene oxide were initially brominated and then transformed to the desired functional groups. The good dispersion of metal nanoparticles over functionalized carbon substrates (particle size less than 5 nm) with good durability, even at a limited functionalization degree (less than 7%) has been demonstrated by morphological and structural studies. The durability of the catalysts was much improved via strong coordination between the metal and nitrogen or sulfur atoms. Impressively, the catalytic activity of platinum nanoparticles on aminated reduced graphene oxide was found to be much better than that on thiolated graphene oxide despite the weaker affinity between amine and noble metals. These findings support further developing new graphene derivatives with the desired functionalization for electronics and energy applications..

Microwave-Assisted Synthesis of Highly Active Single-Atom Fe/N/C Catalysts for High-Performance Aqueous and Flexible All-Solid-State Zn-Air Batteries

The development of low-cost single-atom electrocatalysts for oxygen reduction reaction (ORR) is highly desired but remains a grand challenge. Superior to the conventional techniques, a microwave-assisted strategy is reported for rapid production of high-quality Fe/N/C single-atom catalysts (SACs) with profoundly enhanced reaction rate and remarkably reduced energy consumption. The as-synthesized catalysts exhibit an excellent ORR performance with a positive half-wave potential up to 0.90 V, a high turnover frequency of 0.76 s-1 , as well as a satisfied stability with a lost half-wave potential of just 27 mV over 9000 cycles (much better than that of Pt/C with 107 mV lost) and good methanol resistance. The open-circuit voltages of as-constructed aqueous and flexible all-solid-state Zn-air batteries (ZABs) are 1.56 and 1.52 V, respectively, higher than those of 20% Pt/C-based ones (i.e., 1.43 and 1.38 V, respectively). Impressively, they afford a peak power density of 235 mW cm-2 , which exceeds that of Pt/C (i.e., 186 mW cm-2 ), and is comparable to the best ones of Fe/N/C-based ZABs ever reported.

Electrochemical Crosslinking of Alginate-Towards Doped Carbons for Oxygen Reduction

Electrochemical crosslinking of alginate strands by in situ iron oxidation was explored using a potentiostatic regime. Carbon-based materials co-doped with iron, nitrogen, and/or sulfur were prepared via electrolyte composition variation with a nitrogen-rich compound (rivanol) or through post-treatments with sodium sulfide. Nanometer-sized iron particles were confirmed by transmission and field emission scanning electron microscopy in all samples as a consequence of the homogeneous dispersion of iron in the alginate scaffold and its concomitant growth-limiting effect of alginate chains. Raman spectra confirmed a rise in structural disorder with rivanol/Na2S treatment, which points to more defect sites and edges known to be active sites for oxygen reduction. Fourier transform infrared (FTIR) spectra confirmed the presence of different iron, nitrogen, and sulfur species, with a marked difference between Na2S treated/untreated samples. The most positive onset potential (-0.26 V vs. saturated calomel electrode, SCE) was evidenced for the sample co-doped with N, S, and Fe, surpassing the activity of those with single and/or double doping. The mechanism of oxygen reduction in 0.1 M KOH was dominated by the 2e- reduction pathway at low overpotentials and shifted towards complete 4e- reduction at the most negative explored values. The presented results put forward electrochemically formed alginate gels functionalized by homogeneously dispersed multivalent cations as an excellent starting point in nanomaterial design and engineering.

Metal-free Sulfur-doped graphitic carbon nitride-modified GCE-based electrocatalyst for the enhanced electrochemical determination of Omeprazole in Drug formulations and Biological Samples

This study presents a novel sulfur-doped graphitic carbon nitride (S@g-C₃ N₄ ) with a wider potential range as electrocatalyst for electrochemical sensor application. The S@g-C₃ N₄ nanosheets were successfully prepared with a ball milling method by mixing appropriate molar concentration required precursors. The as-synthesized heteroatom-doped graphitic carbon nitride is characterized by spectroscopic techniques including PL, DRS-UV, FT-IR, and Brunauer-Emmett-Teller equation. The morphological features were studied by FE-SEM and HR-TEM analysis. Chit-S@g-C₃ N₄ -modified glassy carbon electrode (GCE) was employed for the electrochemical detection of omeprazole (OMZ) use in drug formulations. We have noted an oxidation peak current response at a potential of +0.8 V versus Ag/AgCl in PBS medium (0.1 M, pH 7.0). Differential pulse voltammetry amperometry experimental method can be used to measure the concentration of OMZ for quantitative studies in known samples. Under the optimized experimental condition, the calibration plot was constructed by plotting the peak currents versus OMZ in the linear ranges from 6.0 × 10^-7 to 26 × 10^-5  M. The linear regression equation is estimated to be I_p (μA) = 0.9518 (C/μM) + 0.3340 with a good correlation coefficient of 0.9996. The lower determination limit was found to be 20 nM and the current sensitivity was calculated (31.722 μA μM^-1  cm^-2 ). The developed sensor was utilized successfully to determine the OMZ concentration in drug formulations and biological fluids. These results revealed that the Chit-S@g-C₃ N₄ -modified GCE showed excellent electroanalytical performance for the detection of OMZ at a low LOD, wider linear range, high sensitivity, good reproducibility, long-term storage stability, and selectivity with an acceptable relative standard deviation value.

Fast and Versatile Functionalization of Glassy Carbon

A rapid procedure for the functionalization of glassy carbon surfaces (GCSs) is disclosed. A three-step sequence of bromomethylation, azide displacement, and copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC) allows ethynylated molecules to be attached covalently to the carbon surface through a methylene functional group. Redox-active ethynyl ferrocene and [Ru^II(Cl)(DMSO)(ethynyl-TPA)]¹⁺ (DMSO = dimethylsulfoxide; TPA = tris(2-pyridylmethyl)amine) are attached with high coverages as assessed by cyclic voltammetry, and the elemental composition of the surface is confirmed by X-ray photoelectron spectroscopy. In less than 1 h, surface coverages of 1 × 10¹⁴ molecules/cm² are possible that exhibit good durability in both acidic and basic media. Attached [Ru^II(Cl)(DMSO)(ethynyl-TPA)]¹⁺ catalytically oxidizes alcohols, yet the currents and potentials are less impressive compared to an attachment without the intervening methylene group. The advantages of this covalent attachment procedure for GCSs are its short reaction times, mild reaction conditions, and the use of standard laboratory reagents and glassware, allowing for many types of ethynylated molecules to be attached rapidly to the surface.

Lotus-biowaste derived sulfur/nitrogen-codoped porous carbon as an eco-friendly electrocatalyst for clean energy harvesting

Recent research is focused on biomass-derived porous carbon materials for energy harvesting (hydrogen evolution reaction) because of their cost-effective synthesis, enriched with heteroatoms, lightweight, and stable properties. Here, the synthesis of porous carbon (PC) materials from lotus seedpod (LP) and lotus stem (LS) is reported by the pyrolysis method. The porous and graphitic structure of the prepared LP-PC and LS-PC materials were confirmed by field emission scanning electron microscopy, transmission electron microscopy with selected area electron diffraction, X-ray diffraction, and nitrogen adsorption-desorption measurements. Heteroatoms in LP-PC and LS-PC materials were investigated by attenuated total reflection-Fourier transform infrared and X-ray photoelectron spectroscopy. The specific surface area of LP-PC and LS-PC were calculated as 457 and 313 m² g^-1, respectively. Nitrogen and sulfur enriched LP-PC and LS-PC materials were found to be effective electrocatalysts for hydrogen evolution reactions. LP-PC catalyst showed a very low overpotential of 111 mV with the Tafel slope of 69 mV dec^-1, and LS-PC catalyst achieved a Tafel slope of 85 mV dec^-1 with a low overpotential of 135 mV. This work is expected to be extended for the development of biomass as a sustainable porous carbon electrocatalyst with a tunable structure, elements, and electronic properties. Furthermore, preparing carbon materials from the biowaste and applying clean energy harvesting might reduce environmental pollution.

The Development of High-Performance Platinum-Ruthenium Catalysts for the Methanol Oxidation Reaction: Gram-Scale Synthesis, Composition, Morphology, and Functional Characteristics

To obtain the PtRu/C electrocatalysts, the surfactant-free (wet) synthesis methods have been used. The structural-morphological characteristics and electrochemical behavior of the catalysts have been studied. The possibility of ranging the crystallite size from 1.2 to 4.5 nm using different reducing agents (ethylene glycol, ethanol, and isopropanol) has been shown. The effect of both the particles’ size and the mass fraction of the metal component on the electrochemical surface area (ESA), activity in the methanol electrooxidation reaction (MOR), and tolerance to its intermediate products has been studied. The simple and scalable surfactant-free synthesis method of the highly active PtRu/C electrocatalysts with a different mass fraction of metals, with their tolerance to intermediate products of the oxidation being 2.3 times higher than the commercial analogue, has been first proposed. The authors have succeeded in obtaining the PtRu/C catalysts with the nanoparticles’ size of less than 2 nm, characterized by the ultranarrow size and uniform spatial distributions over the support surface, thus having the ESA of more than 90 m2gPtRu−1.

Methanol Oxidation at Platinum Coated Black Titania Nanotubes and Titanium Felt Electrodes

Optimized Pt-based methanol oxidation reaction (MOR) anodes are essential for commercial direct methanol fuel cells (DMFCs) and methanol electrolyzers for hydrogen production. High surface area Ti supports are known to increase Pt catalytic activity and utilization. Pt has been deposited on black titania nanotubes (bTNTs), Ti felts and, for comparison, Ti foils by a galvanic deposition process, whereby Pt(IV) from a chloroplatinate solution is spontaneously reduced to metallic Pt (at 65 °C) onto chemically reduced (by CaH2) TNTs (resulting in bTNTs), chemically etched (HCl + NaF) Ti felts and grinded Ti foils. All Pt/Ti-based electrodes prepared by this method showed enhanced intrinsic catalytic activity towards MOR when compared to Pt and other Pt/Ti-based catalysts. The very high/high mass specific activity of Pt/bTNTs (ca 700 mA mgPt−1 at the voltammetric peak of 5 mV s−1 in 0.5 M MeOH) and of Pt/Ti-felt (ca 60 mA mgPt−1, accordingly) make these electrodes good candidates for MOR anodes and/or reactive Gas Diffusion Layer Electrodes (GDLEs) in DMFCs and/or methanol electrolysis cells.

Facile electrooxidation of ethanol on reduced graphene oxide supported Pt-Pd bimetallic nanocomposite surfaces in acidic media

Development of electrocatalysts with extended homogeneity and improved metal-support interactions is of urgent scientific need in the context of electrochemical energy applications. Herein, bimetallic Pt-Pd nanoparticles with good homogeneity are fabricated using a convenient solution phase chemical reduction method onto a reduced graphene oxide (rGO) support. X-ray diffraction studies revealed that Pt-Pd/rGO possesses the crystallite size of 3.1 nm. The efficacies of Pt-Pd/rGO catalyst (20 wt% Pt + 10 wt% Pd on rGO support, Pt:Pd atomic ratio = 1:1) towards ethanol electrooxidation reaction (EOR) are evaluated in acidic conditions by cyclic voltammetry using catalyst-coated glassy carbon electrode as a working electrode. With the better dispersion on rGO support the Pt-Pd/rGO nancomposite catalyst exhibit highest mass specific activity (0.358 mA/µg-Pt) which is observed to be 1.9 times of similarly synthesized 20 wt% Pt/rGO (0.189 mA/µg-Pt) and 2.5 times of commercial 20 wt% Pt/C (0.142 mA/µg-Pt), respectively. Apart from the observed improved EOR activity, the Pt-Pd/rGO catalyst exhibited better stability than Pt/rGO and Pt/C catalysts. Strong synergy offered by Pt, Pd and rGO support could contribute to the observed higher EOR activity of Pt-Pd/rGO.

Passive Small Direct Alcohol Fuel Cells for Low-Power Portable Applications: Assessment Based on Innovative Increments since 2018

Passive small direct alcohol fuel cells (PS-DAFCs) are compact, standalone devices capable of electrochemically converting the chemical energy in the fuel/alcohol into electricity, with low pollutant emissions and high energy density. Thus, PS-DAFCs are extremely attractive as sustainable/green off-grid low-power sources (milliwatts to watts), considered as alternatives to batteries for small/portable electric and electronic devices. PS-DAFCs benefit from long life operation and low cost, assuring an efficient and stable supply of inherent non-polluting electricity. This review aims to assess innovations on PS-DAFC technology, as well as discuss the challenges and R&D needs covered on practical examples reported in the scientific literature, since 2018. Hence, this compilation intends to be a guidance tool to researchers, in order to help PS-DAFCs overcome the barriers to a broad market introduction and consequently become prime renewable energy converters and autonomous micropower generators. Only by translating research discoveries into the scale-up and commercialization process of the technology can the best balance between the economic and technical issues such as efficiency, reliability, and durability be achieved. In turn, this will certainly play a crucial role in determining how PS-DAFCs can meet pressing sustainable energy needs.

Free-Standing, Interwoven Tubular Graphene Mesh-Supported Binary AuPt Nanocatalysts: An Innovative and High-Performance Anode Methanol Oxidation Catalyst

Pt-based alloy or bimetallic anode catalysts have been developed to reduce the carbon monoxide (CO) poisoning effect and the usage of Pt in direct methanol fuel cells (DMFCs), where the second metal plays a role as CO poisoning inhibitor on Pt. Furthermore, better performance in DMFCs can be achieved by improving the catalytic dispersion and using high-performance supporting materials. In this work, we introduced a free-standing, macroscopic, interwoven tubular graphene (TG) mesh as a supporting material because of its high surface area, favorable chemical inertness, and excellent conductivity. Particularly, binary AuPt nanoparticles (NPs) can be easily immobilized on both outer and inner walls of the TG mesh with a highly dispersive distribution by a simple and efficient chemical reduction method. The TG mesh, whose outer and inner walls were decorated with optimized loading of binary AuPt NPs, exhibited a remarkably catalytic performance in DMFCs. Its methanol oxidation reaction (MOR) activity was 10.09 and 2.20 times higher than those of the TG electrodes with only outer wall immobilized with pure Pt NPs and binary AuPt NPs, respectively. Furthermore, the catalyst also displayed a great stability in methanol oxidation after 200 scanning cycles, implying the excellent tolerance toward the CO poisoning effect.

Promising Electrocatalytic Water and Methanol Oxidation Reaction Activity by Nickel Doped Hematite/Surface Oxidized Carbon Nanotubes Composite Structures

Tailoring the precise construction of non-precious metals and carbon-based heterogeneous catalysts for electrochemical oxygen evolution reaction (OER) and methanol oxidation reaction (MOR) is crucial for energy conversion applications. Herein, this work reports the composite of Ni doped Fe₂ O₃ (Ni-Fe₂ O₃ ) with mildly oxidized multi-walled CNT (O-CNT) as an outstanding Mott-Schottky catalyst for OER and MOR. O-CNT acts as a co-catalyst which effectively regulates the charge transfer in Ni-Fe₂ O₃ and thus enhances the electrocatalytic performance. Ni-Fe₂ O₃ /O-CNT exhibits a low onset potential of 260 mV and overpotential 310 mV @ 10 mA cm^-2 for oxygen evolution. Being a Mott-Schottky catalyst, it achieves the higher flat band potential of -1.15 V with the carrier density of 0.173×10²⁴  cm^-3 . Further, in presence of 1 M CH₃ OH, it delivers the MOR current density of 10 mA cm^-2 at 1.46 V vs. RHE. The excellent electrocatalytic OER and MOR activity of Ni-Fe₂ O₃ /O-CNT could be attributed to the synergistic interaction between Ni-doped Fe₂ O₃ and O-CNT.

Two-Dimensional Palladium Phosphoronitride for Oxygen Reduction

Two-dimensional (2D) catalysts often show extraordinary activity at low mass loading since almost all their atoms are exposed to electrolyte. Palladium (Pd) holds great promise for catalyzing oxygen reduction reaction (ORR) but 2D Pd-based ORR catalyst has rarely been reported. Herein, 2D ternary palladium phosphoronitride (Pd₃P₂N_x) is synthesized, for the first time, for ORR catalysis. The synthesis is guided by a rational design using first-principles density functional theory calculations, and then realized via a postsynthesis substitutional doping of ternary palladium thiophosphate (Pd₃P₂S₈), which almost completely replaces sulfur atoms by nitrogen atoms without destroying the 2D morphology. The doping process exposes the interlocked Pd atoms of Pd₃P₂S₈ and introduces ligands that improve the affinity of oxygen intermediates, resulting in greater kinetics and lower activation energy for ORR. The mass activity of the pristine Pd₃P₂S₈ is dramatically increased as much as 5-fold (from 0.03 to 0.151 mA μg^-1 _Pd in Pd₃P₂N_x). The ORR diffusion-limited current density of Pd₃P₂N_x (6.2 mA cm^-2) exceeds that of commercial Pt/C, and it shows fast kinetics and robust long-term stability. Our theoretical calculations not only guide the experimental doping process, but also provides insights into the underlying mechanism of the outstanding ORR activity and stability.

Electrochemical preparation of monodisperse Pt nanoparticles on a grafted 4-aminothiophenol supporting layer for improving the MOR reaction

The methanol oxidation reaction (MOR) has recently gained a lot of attention due to its application in fuel cells and electrochemical sensors. To enhance the MOR, noble metal nanoparticles should be homogeneously dispersed on the electrode surface with the aid of one suitable support. In this work, 4-aminothiophenol (4-ATP) molecules which contain simultaneously amine and thiol groups were electro-grafted onto the electrode surface to provide anchoring sites, limit aggregation and ensure good dispersion of metal nanoparticles. The results showed a high density of platinum nanoparticles (PtNPs) with an average size of 25 nm on the glassy electrode modified with a 4-ATP supporting layer. Consequently, the MOR was improved by 2.1 times with the aid of the grafted 4-ATP layer. The electrochemical sensor based on PtNPs/4-ATP/GCE is able to detect MeOH in a linear range from 1.26 to 21.42 mM with a detection limit of 1.21 mM.

Synergy between iron oxide sites and nitrogen-doped carbon xerogel/diamond matrix for boosting the oxygen reduction reaction

The innovative design and facile synthesis of efficient and stable electrocatalysts for the oxygen reduction reaction (ORR) are crucial in the field of fuel cells. Herein, the facile synthesis of an iron oxide@nitrogen-doped carbon diamond (FeO x @NCD) composite via an effective pyrolysis strategy is reported. The properties of this electrocatalyst, including a high density of active sites, nitrogen doping, accessible surface area, well dispersed pyramidal morphology of the iron oxide, and the porous structure of the carbon matrix, promote a highly active oxygen reduction reaction (ORR) performance. The electrocatalyst exhibits outstanding stability, with a half-wave potential of 0.692 V in alkaline solution (0.1 M KOH), as well as a limiting current density of -31.5 mA cm-2 at 0.17 V vs. RHE. This study highlights the benefits of hybridizing sp2 carbon xerogel and sp3 diamond carbon allotropes with iron oxide to boost the ORR activity. The proposed strategy opens up an avenue for designing advanced carbon-supported metal oxide catalysts that exhibit excellent electrocatalytic performance.

The Water-Based Synthesis of Platinum Nanoparticles Using KrF Excimer Laser Ablation

Our work presents, for the first time, a comprehensive study of the synthesis of fully metallic platinum nanoparticles (Pt-NPs) involving the ablation process in double distilled water using a KrF excimer laser. To obtain detailed information on Pt-NP morphology and optical properties, prepared colloids were characterized using High Resolution Scanning Transmission Electron Microscopy (HR-STEM) with advanced capabilities for Energy Dispersive X-ray Analysis (EDX), UV/Vis optical spectroscopy, and Direct Analysis in Real Time-Mass Spectrometry (DART-MS). The influence of the applied laser fluence and laser repetition rate (RR) values on the characteristics of the obtained Pt-NPs and the ablation process, respectively, were also analyzed. Spherical and spherical-like nanoparticles exhibiting aggregation were produced. The Pt-NP mean size values were between 2.2 ± 1.2 nm and 4.0 ± 1.0 nm, while their interplanar distance measurements showed a face-centered cubic (FFC) Pt lattice (111), as revealed by HR-STEM measurements, for all investigated samples. The smallest mean size of 2.2 nm of the Pt-NPs was obtained using a 2.3 J cm-2 laser fluence at a 10 Hz RR, and the narrowest size distribution of the NPs was obtained with a 2.3 J cm-2 laser fluence at a 40 Hz RR. A linear dependence of the Pt-NP diameters versus the laser repetition rate was found at a constant fluence of 2.3 J cm-2. The proposed eco-friendly synthesis route of Pt-NPs, because of its relative simplicity, has the potential for use in industrial production.

Recent Advancements in the Synthesis and Application of Carbon-Based Catalysts in the ORR

Fuel cells are a promising alternative to non-renewable energy production industries such as petroleum and natural gas. The cathodic oxygen reduction reaction (ORR), which makes fuel cell technology possible, is sluggish under normal conditions. Thus, catalysts must be used to allow fuel cells to operate efficiently. Traditionally, platinum (Pt) catalysts are often utilized as they exhibit a highly efficient ORR with low overpotential values. However, Pt is an expensive and precious metal, posing economic problems for commercialization. Herein, advances in carbon-based catalysts are reviewed for their application in ORRs due to their abundance and low-cost syntheses. Various synthetic methods from different renewable sources are presented, and their catalytic properties are compared. Likewise, the effects of heteroatom and non-precious metal doping, surface area, and porosity on their performance are investigated. Carbon-based support materials are discussed in relation to their physical properties and the subsequent effect on Pt ORR performance. Lastly, advances in fuel cell electrolytes for various fuel cell types are presented. This review aims to provide valuable insight into current challenges in fuel cell performance and how they can be overcome using carbon-based materials and next generation electrolytes.

Enhanced Electrocatalytic Oxidation of Small Organic Molecules on Platinum-Gold Nanowires: Influence of the Surface Structure and Pt-Pt/Pt-Au Pair Site Density

The electrochemical oxidation of small organic molecules (SOMs) such as methanol and glucose is a critical process and has relevant applications in fuel cells and sensors. A key challenge in SOM oxidation is the poisoning of the surface by carbon monoxide (CO) and other partially oxidized intermediates, which is attributed to the presence of Pt-Pt pair sites. A promising pathway for overcoming this challenge is to develop catalysts that selectively oxidize SOMs via "direct" pathways that do not form CO as a primary intermediate. In this report, we utilize an ambient, template-based approach to prepare PtAu alloy nanowires with tunable compositions. X-ray photoelectron spectroscopy measurements reveal that the surface composition matches that of the bulk composition after synthesis. Monte Carlo method simulations of the surface structure of PtAu alloys with varying coverage of oxygen adsorbates and varying degrees of oxygen adsorption strength reveal that oxygen adsorption under electrochemical conditions enriches the surface with Pt and a large fraction of Pt-Pt sites remain on the surface even with the Au content of up to 50%. Electrochemical properties and the catalytic performance measurements of the PtAu nanowires for the oxidation of methanol and glucose reveal that the mechanistic pathways that produce CO are suppressed by the addition of relatively small quantities of Au (∼10%), and CO formation can be completely suppressed by 50% Au. The suppression of CO formation with small quantities of Au suggests that the presence of Pt-Au pair sites may be more important in determining the mechanism of SOM oxidation rather than Pt-Pt pair site density.

Tunable Assembly of Protein Enables Fabrication of Platinum Nanostructures with Different Catalytic Activity

Proteins are promising biofunctional units for the construction of nanomaterials (NMs) due to their abundant binding sites, intriguing self-assembly properties, and mild NM synthetic conditions. Tobacco mosaic virus coat protein (TMVCP) is a protein capable of self-assembly into distinct morphologies depending on the solution pH and ionic strength. Herein, we report the use of TMVCP as a building block to organize nanosized platinum into discrete nanorings and isolated nanoparticles by varying the solution pH to modulate the protein assembly state. Compared with a commercial Pt/C catalyst, the TMVCP-templated platinum materials exhibited significant promotion of the catalytic activity and stability toward methanol electrooxidation in both neutral and alkaline conditions. The enhanced catalytic performance is likely facilitated by the protein support. Additionally, Pt nanorings outperformed isolated nanoparticles, although they are both synthesized on TMVCP templates. This could be due to the higher mechanical stability of the protein disk structure and possible cooperative effects between adjacent nanoparticles in the ring with narrow interparticle spacing.

Properties of the Pt(111)/electrolyte electrochemical interface studied with a hybrid DFT-solvation approach

Self-consistent modeling of the interface between solid metal electrode and liquid electrolyte is a crucial challenge in computational electrochemistry. In this contribution, we adopt the effective screening medium reference interaction site method (ESM-RISM) to study the charged interface between a Pt(111) surface that is partially covered with chemisorbed oxygen and an aqueous acidic electrolyte. This method proves to be well suited to describe the chemisorption and charging state of the interface at controlled electrode potential. We present an in-depth assessment of the ESM-RISM parameterization and of the importance of computing near-surface water molecules explicitly at the quantum mechanical level. We found that ESM-RISM is able to reproduce some key interface properties, including the peculiar, non-monotonic charging relation of the Pt(111)/electrolyte interface. The comparison with independent theoretical models and explicit simulations of the interface reveals strengths and limitations of ESM-RISM for modeling electrochemical interfaces.

Enhanced Methanol Oxidation Activity of PtRu/C100−xMWCNTsx (x = 0–100 wt.%) by Controlling the Composition of C-MWCNTs Support

PtRu nanoparticles decorated on carbon-based supports are of great interest for direct methanol fuel cells (DMFCs). In this study, PtRu alloy nanoparticles decorated on carbon Vulcan XC-72 (C), multi-walled carbon nanotubes (MWCNTs), and C-MWCNTs composite supports were synthesized by co-reduction method. As a result, PtRu nanoparticles obtained a small mean size (dmean = 1.8–3.8 nm) with a size distribution of 1–7 nm. We found that PtRu/C60MWCNTs40 possesses not only high methanol oxidation activity, but also excellent carbonaceous species tolerance ability, suggesting that C-MWCNTs composite support is better than either C or MWCNTs support. Furthermore, detailed investigation on PtRu/C100−xMWCNTsx (x = 10–50 wt.%) shows that the current density (Jf), catalyst tolerance ratio (Jf/Jr), and electron transfer resistance (Ret) are strongly affected by C-MWCNTs composition. The highest Jf is obtained for PtRu/C70MWCNTs30, which is considered as an optimal electrocatalyst. Meanwhile, both PtRu/C70MWCNTs30 and PtRu/C60MWCNTs40 exhibit a low Ret of 5.31–6.37 Ω·cm2. It is found that C-MWCNTs composite support is better than either C or MWCNTs support in terms of simultaneously achieving the enhanced methanol oxidation activity and good carbonaceous species tolerance.

Influence of Solvents on the Electroactivity of PtAl/rGO Catalyst Inks and Anode in Direct Ethanol Fuel Cell

This paper presents research on the effects of common solvents such as n-butyl acetate, isopropanol, and ethanol on the properties and electroactivity of catalyst ink based on PtAl/rGO. The inks prepared by mixing PtAl/rGO catalyst, Nafion solution (5 wt%), and solvent were coated on carbon cloth by the spin coating method. The results obtained showed that ethanol was the most suitable solvent for the preparation of catalyst ink with a volume ratio between catalyst slurry and solvent of 1 : 1 (CI-EtOH (1/1) ink). The surface of the CI-EtOH (1/1) coated electrode was smooth, flat, and even and had no cracks due to the increase of Nafion mobility, resulting in significant improvement in the interaction between Pt particles and ionomer. Moreover, the electrochemical activity of the CI-EtOH (1/1) ink in ethanol electrooxidation reaction, in both acidic and alkaline media, has the highest value, with the forward current density, IF, reaching 1793 mA mgPt−1 and 4751 mA mgPt−1, respectively. In the application in direct ethanol fuel cell (DEFC), the CI-EtOH ink-coated anode also exhibited the highest power density in both PEM-DEFC (with a proton exchange membrane) and AEM-DEFC (with an anion exchange membrane) at 19.10 mW cm−2 and 27.07 mW cm−2, respectively.

Carbon Nanotube Films for Energy Applications

This perspective article describes the application opportunities of carbon nanotube (CNT) films for the energy sector. Up to date progress in this regard is illustrated with representative examples of a wide range of energy management and transformation studies employing CNT ensembles. Firstly, this paper features an overview of how such macroscopic networks from nanocarbon can be produced. Then, the capabilities for their application in specific energy-related scenarios are described. Among the highlighted cases are conductive coatings, charge storage devices, thermal interface materials, and actuators. The selected examples demonstrate how electrical, thermal, radiant, and mechanical energy can be converted from one form to another using such formulations based on CNTs. The article is concluded with a future outlook, which anticipates the next steps which the research community will take to bring these concepts closer to implementation.