Platinum-based Electrocatalysts Research Articles

Carbon dots modified molybdenum disulfide as a high-efficiency hydrogen evolution electrocatalyst

Molybdenum disulfide (MoS2) is considered a low-cost material that may replace platinum-based electrocatalysts towards hydrogen evolution reaction (HER). However, the catalytic activity of MoS2 is limited by the low conductivity and lack of active sites. Here, a biomass carbon dots-molybdenum disulfide (BCDs-MoS2) composite was synthesized as a HER catalyst by a simple hydrothermal method. The BCDs-MoS2 catalyst displayed excellent electrocatalytic performance for HER with lower onset overpotential (115 mV), smaller Tafel slope (56.57 mV dec−1) as well as high cycling stability, which superior to those of homemade MoS2, commercial MoS2, and most of the reported MoS2-based catalysts. According to the characterization results of morphology, surface properties, and valence states of elements, the outstanding catalytic activity of BCDs-MoS2 is ascribed to its loose structure with a large specific surface area along with abundant edges and defects, and the increase in the amount of S22− and S2− which possess higher activity due to the addition of the BCDs. This study can afford a new strategy to design high performance HER catalysts.

Engineered interfaces of WSe2/rhenium doped SnSe2 heterostructures nanosheet arrays for superior hydrogen generation and flexible supercapacitor

Two-dimensional hybrid heterostructures offer substantial benefits in electrochemical energy storage and conversion due to their unique compositional and structural features. It is a low-cost alternative to widely used platinum-based electrocatalysts for the commercialization approach. However, making heterostructures with other semiconductor materials bound together by van der Waals or covalent interactions is practically challenging. Here we report a hybrid electrocatalyst prepared by the hydrothermal growth of WSe2 nanosheet arrays decorated by rhenium (Re)-doped tin diselenide (SnSe2) (WSe2@ReSnSe2). The vertically aligned high-density arrays expose more active sites and promote the charge/ion transfer due to the open porous space inside the array of hybrid heterostructure composite. Moreover, the Re doping improves the electron transfer by shifting Fermi level and also provides an active site to enhance catalytic activity. As demonstrated, WSe2@ReSnSe2 hybrid heterostructure exhibits excellent and stable catalytic activity for hydrogen evolution with the overpotential and Tafel slope of 193 mV and 66 mV/dec in acidic medium. The fabricated flexible supercapacitor based on a hybrid heterostructure catalyst achieves the specific capacitance (Csp) of 175 F/g at a current density of 1 A/g with Csp retention rate of 84.6% after the 5,000 cycles at 10 A/g.

Atomic-Level Pt Electrocatalyst Synthesized via Iced Photochemical Method for Hydrogen Evolution Reaction with High Efficiency.

In heterogeneous catalysis, metal particle morphology and size can influence markedly the activity. It is of great significance to rationally design and control the synthesis of Pt at the atomic level to demonstrate the structure-activity relationship toward electrocatalysis. Herein, a powerful strategy is reported to synthesize graphene-supported platinum-based electrocatalyst, that is, nanocatalysts with controllable size can be prepared by iced photochemical method, including single atoms (Pt-SA@HG), nanoclusters (Pt-Clu@HG), and nanocrystalline (Pt-Nc@HG). The Pt-SA@HG exhibits unexpected electrocatalytic hydrogen evolution reaction (HER) performances with 13mV overpotential at 10mAcm-2 current densities which surpass Pt-Clu@HG and Pt-Nc@HG. The in situ X-ray absorption fine structure spectroscopy (XAFS) and density functional theory (DFT) calculations determine the Pt-C3 active site is linchpin to the excellent HER performance of Pt-SA@HG. Compared with the traditional Pt-Nx coordination structure, the pure carbon coordinated Pt-C3 site is more favorable for HER. This work opens up a new way to adjust the metal particle size and catalytic performance of graphene at a multiscale level.

Graphene-Derived Carbon Support Boosts Proton Exchange Membrane Fuel Cell Catalyst Stability.

The lack of efficient and durable proton exchange membrane fuel cell electrocatalysts for the oxygen reduction reaction is still restraining the present hydrogen technology. Graphene-based carbon materials have emerged as a potential solution to replace the existing carbon black (CB) supports; however, their potential was never fully exploited as a commercial solution because of their more demanding properties. Here, a unique and industrially scalable synthesis of platinum-based electrocatalysts on graphene derivative (GD) supports is presented. With an innovative approach, highly homogeneous as well as high metal loaded platinum-alloy (up to 60 wt %) intermetallic catalysts on GDs are achieved. Accelerated degradation tests show enhanced durability when compared to the CB-supported analogues including the commercial benchmark. Additionally, in combination with X-ray photoelectron spectroscopy Auger characterization and Raman spectroscopy, a clear connection between the sp2 content and structural defects in carbon materials with the catalyst durability is observed. Advanced gas diffusion electrode results show that the GD-supported catalysts exhibit excellent mass activities and possess the properties necessary to reach high currents if utilized correctly. We show record-high peak power densities in comparison to the prior best literature on platinum-based GD-supported materials which is promising information for future application.

(Digital Presentation) Improving Oxygen Evolution Reaction Performance and Durability Using Rhombic Dodecahedral Pt3(Ni,X) Nanoparticles with Metal Oxide Supports

The supply infrastructure and production of hydrogen remains a limiting aspect in the introduction of polymer electrolyte fuel cell (PEFC) technologies.[1] The creation of highly efficient electrocatalysts is limited by predominantly carbon-based support systems which corrode readily during the oxygen evolution reaction (OER).[2] In acidic environments, iridium and ruthenium electrocatalysts with unary, binary, and ternary compositions have been used to achieve excellent OER results, however, carbon corrosion remains an issue for performance over long periods of time. The objective of this work is to examine the effect of highly active ternary based Pt3(Ni,X) rhombic dodecahedral nanoframes loaded onto metal oxide supports.Novel platinum-based electrocatalysts have been developed to improve catalytic activity and overall durability in acidic environments. Of note is the creation of binary Pt3Ni in a rhombic dodecahedral shape with a Pt skin synthesized.[3] These nanoparticles demonstrate very high specific/mass activities and are comparably durable over 10,000 potential cycles.Previous work[4] has been able to recreate the Pt3Ni rhombic dodecahedron under different synthesis conditions allowing for more rapid manufacture. These nanoparticles were used in combination with nitrogen-doped carbon support to examine the effects of surface nitrogen as anchoring sites. Examination using XPS, electrochemical stripping, and SEIRAS shows that the nitrogen sites alter the d-band center of surface Pt in addition to creating a more homogenous distribution of the nanoparticles. The addition of a ternary element allows for additional fine tuning of the d-band center of platinum near the particle surface.The oxygen evolution reaction requires a higher potential range which leaves carbon-based support systems susceptible to corrosion.[2] Several metal oxide support systems have been investigated as potential candidates, with a particular focus on material conductivity. Antimony tin oxide (ATO) shows promise as a relatively conductive metal oxide support for OER applications.[2] Furthermore, ATO shows lower dissolution rates when compared to other tin oxides in similar acidic environments.[5] As mentioned, iridium and ruthenium are used predominantly for OER in acidic environments. Therefore, the ternary metal additions (X) used in this work include PtNiIr and PtNiRu based nanoframes. These nanoframes have been successfully loaded onto ATO metal oxide supports. These catalyst support systems show promising OER results, even when compared to carbon supported NFs, as well as excellent durability. Examination was done using Scanning Tunneling Electron Microscopy (STEM), X-ray Photoelectron Spectroscopy (XPS), X-ray Diffraction (XRD), X-ray absorption spectroscopy (XAS), and rotating disk electrode (RDE) electrochemical measurement. This work could lead to significant improvements into electrocatalyst activity and durability which are necessary to implement PEFC technology onto a global scale.

(Digital Presentation) Effects of Foreign Elements Added Oxide-Based Electrocatalyst for Oxygen Reduction Reaction as Non-Precious Metel Cathodes

On Dec. 2020, new MIRAI of fuel cell vehicle (FCV) from Toyota started to sell in Japan. However, the price of new model is almost same as previous model. For wide commercialization of FCV, it should be required for more development. One of the barriers of innovative system for the FCV is conventional platinum-based electrocatalyst. The cost of Pt is very expensive due to its very poor resources. Moreover, the conventional Pt-based electrocatalyst cannot reach enough performance for next generation FCV that is proposed in new roadmap released from NEDO, Japan. From this point of view, the non-precious metal electrocatalyst should be required for the breakthrough against above issue. We have focused and studied group 4 and 5 metal oxide-based electrocatalyst as non-platinum catalysts for the oxygen reduction reaction (ORR) because of low-cost, abundant reserves, and high stability in acidic electrolytes [1-2]. We found that titanium oxide prepared from TiOTPyzPz supported on multi-walled carbon nanotubes had superior ORR activity [3]. On the other hand, it was published as an international patent that the addition of other elements such as Fe and Ni is affected to enhance the ORR activity of Ti oxide-based electrocatalyst [4]. In this study, we have investigated to apply for the TiOTPyzPz as a starting material with and without Fe, Ni, and Zn addition to enhance the ORR activity of Ti oxide-based electrocatalyst.2,3-Dicyanopyrazine, urea, and Ti isopropoxide were dissolved in quinoline and refluxed to synthesize TiOTPyzPz. Iron acetate, Nickel acetate, and Zinc acetate were also added to dissolve in quinoline to obtain the Fe, Ni, and Zn-added TiOTPyzPz as a starting material. The molar ratio of Ti:Fe:Ni:Zn was set to constant. These starting materials were mixed with carbon nanotube by ball-milling to prepare the precursors. These precursors were heat-treated under low oxygen partial pressure for 3 h to obtain titanium oxide-based catalysts. The catalyst powder was dispersed into 1-propanol with Nafion solution to prepare a catalyst ink. The ink was dropped on a glassy carbon rod, and dried for an hour to use as a working electrode in electrochemical measurement.Electrochemical measurements were performed in 0.5 mol dm-3 H2SO4 at 30 oC with a conventional 3-electrode cell. A reversible hydrogen electrode (RHE) and a glassy carbon plate were used as used as a reference and counter electrode, respectively. Slow scan voltammetry (SSV) was performed at a scan rate of 5 mV s-1 from 0.2 V to 1.2 V vs. RHE under O2 and N2. The ORR current (i ORR) was determined by calculating the difference between the current under O2 and N2.Figure 1 shows the effect of Fe, Ni, and Zn addition to TiOTPyzPz as a starting material on the ORR polarization curves of the titanium oxide-based catalysts. The vertical axis is based on catalyst weight. Ti oxid-based electrocatalyst prepared from Fe, Ni, and Zn addition to TiOTPyzPz (TiOx-Fe, Ni, Zn) resulted in the increase in the onset potential for the ORR and ORR current compared to that without addition (TiOx), revealing that the addition of Fe, Ni, and Zn was found to be effective in improving the ORR activity. XRD pattern of TiOx shows several peaks identified TiO2-Rutile, TiO2-Anatanse and TiO2-Brookite while the XRD pattern of TiOx-Fe, Ni, Zn also shows several peaks identified similar to TiOx. In the case of XRD pattern of TiOx-Fe, Ni, Zn, the peak identified compounds relating to additional elements such as Fe, Ni and Zn does not detect strongly. It is suggested that the addition of Fe, Ni and Zn to TiOTPyzPz conduce to the distortion of crystal phase of TiO2 [5] and it affected to suppress the crystal growth of Ti oxide-based electrocatalyst. These facts are possibly contributed to enhance the ORR activity of TiOx-Fe, Ni, Zn compared to that of TiOx.Acknowledgement: The authors thank New Energy and Industrial Technology Development Organization (NEDO) and ENEOS Tonen General Research / Development Encouragement & Scholarship Foundation for financial support.Reference[1] A. Ishihara, Y. Ohgi, K. Matsuzawa, S. Mitsushima, and K. Ota, Electrochim. Acta, 55, 8005 (2010).[2] A. Ishihara, S. Tominaka, S. Mitsushima, H. Imai, H. Imai, O. Sugino, and K. Ota, Curr. Opin. Electrochem., 21 , 234 (2020).[3] S. Tominaka, A. Ishihara, T. Nagai, and K. Ota, ACS Omega, 2, 5209 (2017).[4] K. Takahashi, T. Imai, R. Monden, Y. Wakisaka, and S. Sato, Oxygen Reduction Catalyst, Process for Producing Same, and Polymer Electrolyte Membrane Fuel Cell, WO/2013/008501.[5] Y. Yamamoto, S. Kasamatsu, and O. Sugino, J. Phys. Chem. C, 123, 19486 (2019). Figure 1

Self-Templating-Oriented Manipulation of Ultrafine Pt3 Cu Alloyed Nanoparticles into Asymmetric Porous Bowl-Shaped Configuration for High-Efficiency Methanol Electrooxidation.

The precise and comprehensive manipulation of the component, size, and geometric nano-architecture of platinum-based electrocatalysts into porous and hollow structure can effectively impart the catalysts with substantially improved electrochemical performance, yet remain formidably challenging. Herein, a straightforward fabrication of porous platinum-copper alloyed nanobowls (abbreviated as Pt3 Cu NBs hereafter) assembled by ultrafine nanoparticles (≈2.9nm) via a one-pot hydrothermal approach with the assistance of a structure-directing agent of N,N'-methylenebisacrylamide (MBAA) is reported. The involvement of MBAA plays a decisive role in the formation of Pt-MBAA complex solid nanospheres, which serve as the self-sacrificial reactive template for the deposition/growth of Pt3 Cu nanoparticles and the eventual formation of the asymmetric open-shelled nanobowls. Benefitting from the 3D sufficient accessibility of exterior/interior surfaces, high atom-utilization efficiency, and PtCu bimetallic alloy synergy, the self-supported Pt3 Cu NBs demonstrate remarkably enhanced activity, better anti-poisoning capability, and reinforced robustness for the methanol oxidation reaction (MOR) as compared with the commercial Pt black benchmark, exhibiting great application promises in practical fuel cell systems. It is envisaged that the innovative self-templated synthetic strategy outlined here may provide a perspective to design a range of porous bowl-shaped high-performance nanocatalysts.

Mechanochemical Synthesis of Fluorine-Containing Co-Doped Zeolitic Imidazolate Frameworks for Producing Electrocatalysts.

Catalysts derived from pyrolysis of metal organic frameworks (MOFs) are promising candidates to replace expensive and scarce platinum-based electrocatalysts commonly used in polymer electrolyte membrane fuel cells. MOFs contain ordered connections between metal centers and organic ligands. They can be pyrolyzed into metal- and nitrogen-doped carbons, which show electrocatalytic activity toward the oxygen reduction reaction (ORR). Furthermore, metal-free heteroatom-doped carbons, such as N-F-Cs, are known for being active as well. Thus, a carbon material with Co-N-F doping could possibly be even more promising as ORR electrocatalyst. Herein, we report the mechanochemical synthesis of two polymorphs of a zeolitic imidazole framework, Co-doped zinc 2-trifluoromethyl-1H-imidazolate (Zn0.9Co0.1(CF3-Im)2). Time-resolved in situ X-ray diffraction studies of the mechanochemical formation revealed a direct conversion of starting materials to the products. Both polymorphs of Zn0.9Co0.1(CF3-Im)2 were pyrolyzed, yielding Co-N-F containing carbons, which are active toward electrochemical ORR.

Seed-Mediated, Shape-Controlled Synthesis Methods for Platinum-Based Electrocatalysts for the Oxygen Reduction Reaction-A Mini Review.

Overcoming the slow oxygen reduction reaction (ORR) kinetics at the cathode of the hydrogen fuel cells requires the use of electrocatalysts containing expensive and scare platinum to achieve reasonable performance, hampering widespread use of the technology due to high material costs and sustainability issues. One option available to tackle this issue is to use new designs to create nanomaterials which achieve excellent electrocatalytic performances and long-lasting stabilities whilst using less platinum than is currently required. Reliably producing nanomaterials with predictable activities and stabilities using simple, safe, and scalable methods is an important research topic to the advancement of fuel cell technologies. The oxygen reduction reaction occurs at the surface of electrocatalytic materials, and since nanomaterial structures exhibit different catalytic activities, their shapes have a strong relationship to the final performance. Seed-mediated synthesis can be used to control the shape of materials with the aim of obtaining products with the most desirable surface properties for the ORR. This review summarized the current advancement of the synthesis of platinum-based ORR and provided the insights for the future development of this field.

Ultrafine platinum nanoparticles supported on N,S-codoped porous carbon nanofibers as efficient multifunctional materials for noticeable oxygen reduction reaction and water splitting performance.

The design of highly active, stable and durable platinum-based electrocatalysts towards the oxygen reduction reaction (ORR), oxygen evolution reaction (OER), hydrogen evolution reaction (HER), and hydrogen adsorption has a high and urgent demand in fuel cells, water splitting and hydrogen storage. Herein, ultrafine platinum nanoparticles (Pt NPs) supported on N,S-codoped porous carbon nanofibers (Pt–N,S-pCNFs) hybrids were prepared through the electrospinning method coupled with hydrothermal and carbonation processes. The ultrafine Pt NPs are sufficiently dispersed and loaded on pCNFs and codoped with N and S, which can improve oxygen adsorption, afford more active sites, and greatly enhance electron mobility. The Pt–N,S-pCNFs hybrid achieves excellent activity and stability for ORR with ∼70 mV positive shift of onset potential compared to the commercial Pt/C-20 wt% electrocatalyst. The long-term catalytic durability with 89.5% current retention after a 10 000 s test indicates its remarkable ORR behavior. Pt–N,S-pCNFs also exhibits excellent HER and OER performance, and can be used as an efficient catalyst for water splitting. In addition, Pt–N,S-pCNFs exhibits an excellent hydrogen storage capacity of 0.76 wt% at 20 °C and 10 MPa. This work provides novel design strategies for the development of multifunctional materials as high-performance ORR catalysts, water splitting electrocatalysts and hydrogen storage materials.

On the deactivation of N-doped carbon materials active sites during oxygen reduction reaction

N-doped carbon materials have been considered one of the most promising options for the replacement of platinum-based electrocatalysts towards the oxygen reduction reaction (ORR). This work provides insights into the deactivation routes of N-doped carbon materials. The changes occurring in the active sites of N-doped carbon catalysts have been analyzed in detail through pre- and post-ORR characterization by XPS of selectively N-doped carbon materials. Moreover, computational modelling was used to deepen into the deactivation mechanism of N-doped carbon materials in the ORR. From XPS and computational modelling, it can be concluded that the deactivation of graphitic-type nitrogen species, during the ORR in both acidic and alkaline environments, occurs through oxidation and tautomerization reactions that result in the formation of N–C–O-type groups. In acidic environment, the reaction kinetics is slower due to the high stability of the ORR intermediates. In alkaline electrolyte, the N–C–O-type groups can be easily formed due to the interaction of graphitic-type N species and the OH− anions from the electrolyte. In this case, the catalytic activity is due to the contribution of both graphitic nitrogen groups and N–C–O species.

Highly active atomically dispersed platinum-based electrocatalyst for hydrogen evolution reaction achieved by defect anchoring strategy

Single-atom catalysts (SACs) can achieve ultimate atomic utilization of precious metals to improve water splitting’s economy. However, active sites in SACs are usually insufficient. Therefore, we propose the use of porous Co1NC which is rich in defects as support to prepare Pt1/Co1NC by mild electrochemical reduction at room temperature. Pt1/Co1NC showed record-high hydrogen evolution reaction (HER) activity, with an overpotential of only 4.15 mV at a current density of 10 mA cm−2. Its mass activity reached 32.4 A mg−1Pt at an overpotential of 20 mV, which is 54 times that of Pt/C. The turnover frequency was up to 32.86 s−1 at 20 mV, with excellent stability in long-term service. Our strategy suggests that nitrogen/carbon defects are vital for anchoring&forming monodispersed Pt active sites while preventing agglomeration. These sites possess low energy barriers, as verified by theoretical simulations. Therefore, our method presents a technical breakthrough for reducing cost of hydrogen energy.

Prudent Practices in ex situ Durability Analysis Using Cyclic Voltammetry for Platinum-based Electrocatalysts.

Platinum (Pt)-based electrocatalysts are at the vanguard of research initiatives to meet activity and durability targets for promoting large-scale adoption of fuel cell vehicles. Ex situ characterization of electrocatalyst activity and durability using cyclic voltammetry (CV) has a steep learning curve. Thus, many researchers who do not receive formal training in electrochemistry are left unsure how to proceed. Herein, we identify and compile prudent practices for reliable assessment of ECSA values with examples from our research on nanoscale catalytic films formed by the self-terminating electrodeposition of Pt. Starting with a conceptual framework to understand typical features in the CV of reversible redox couples, we present prudent practices in acquiring CV data aimed at nonelectrochemists. We then highlight specific features related to ECSA computation from Pt CV. Finally, we suggest safeguards that help avoid missteps and achieve repeatable results while conducting ex situ durability tests that extend over days.

Confining platinum clusters in ZIF-8-derived porous N-doped carbon arrays for high-performance hydrogen evolution reaction

Exploring high efficient electrocatalyst for hydrogen evolution reaction plays a vital role in the sustainable and widespread application of hydrogen fuel. Platinum-based electrocatalysts, as one of the most standout candidates, are limited to large-scale commercial applications attributing to their scarcity, expensive price, poor stability, and inferior durability. Herein, we construct a ZIF-8-derived nitrogen-doped carbon arrays-confined platinum clusters structure, named CTA@Pt@NCBs, on a continuously conducting carbon nanotube arrays substrate. As expected, the prepared CTAs@Pt@NCBs exhibits a low overpotential of 27.42 mV at 10 mA cm−2. More importantly, CTA@Pt@NCBs demonstrate excellent stability and durability, with 97.18% potential retention after 60 h of chronopotentiometric test, higher than that of commercial Pt/C (53.09%), and virtually no decrease in activity after 10, 000 potential cycles. The excellent electrocatalytic performance is mainly attributed to the unique structural features, including confined Pt clusters, porous nitrogen-doped carbon bubbles, continuous conductive carbon nanotube arrays, and binder-free electrode. This work provides a feasible strategy for improving the stability and atom utilization efficiency of platinum-based catalysts, thereby increasing their cost-effectiveness.

Electrocatalytic performance of NiNH2BDC MOF based composites with rGO for methanol oxidation reaction

Present work comprehensively investigated the electrochemical response of Nickel-2 Aminoterephthalic acid Metal–Organic Framework (NiNH2BDC) and its reduced graphitic carbon (rGO) based hybrids for methanol (CH3OH) oxidation reaction (MOR) in an alkaline environment. In a thorough analysis of a solvothermally synthesized Metal–Organic Frameworks (MOFs) and its reduced graphitic carbon-based hybrids, functional groups detection was performed by FTIR, the morphological study by SEM, crystal structure analysis via XRD, and elemental analysis through XPS while electrochemical testing was accomplished by Chronoamperometry (CA), Cyclic Voltametric method (CV), Electrochemically Active Surface Area (EASA), Tafel slope (b), Electron Impedance Spectroscopy (EIS), Mass Activity, and roughness factor. Among all the fabricated composites, NiNH2BDC MOF/5 wt% rGO hybrid by possessing an auspicious current density (j) of 267.7 mA/cm2 at 0.699 V (vs Hg/HgO), a Tafel slope value of 60.8 mV dec−1, EASA value of 15.7 cm2, and by exhibiting resistance of 13.26 Ω in a 3 M CH3OH/1 M NaOH solution displays grander electrocatalytic activity as compared to state-of-the-art platinum-based electrocatalysts.

High-Resolution Nanopatterning Method of Carbon Nanofibers with Transition Metal Oxides for Electrocatalysis and Gas Sensing Applications Using Joule Heating and Chemical Vapor Deposition

In the past decade, there has been significant research on carbon-transition metal oxides (TMO) hybrid structures and their applications as novel catalysts and sensors[1-3]. Some of these research efforts include i) development of alternatives to platinum-based electrocatalysts to generate hydrogen and ii) design of hybrid nanofiber-based sensors having a high surface to volume ratio. Carbon-TMO-based structures are strong candidates to fulfill these needs owing to their catalytic and sensing performance. However, typical synthesis processes of these structures, such as hydrothermal deposition of TMO on carbon, or combined pyrolysis of carbon and TMO precursors, are challenging to control and reproduce.Addressing this controllability issue, we recently developed a highly reproducible process at the wafer level to synthesize carbon-TMO structures, consisting of a suspended Glassy Carbon Wire (GCW) coated with WO3-x[4-5]. A monolithic carbon structure featuring a suspended GCW of known diameter and length is microfabricated by first laying a SU-8 fiber on top of a photopatterned SU-8 scaffold, using the nearfield-electrospinning technique, followed by pyrolysis. The WO3-x coating is deposited via Localized Chemical Vapor deposition (LCVD), activated by controlling the temperature profile on the suspended GCW through Joule heating. The length and thickness of the coating are adjusted by manipulating the current through the GCW and monitoring its voltage. The featured suspended GCW is ideal for understanding and describing the LCVD process of different TMOs on carbon. However, a single microstructure is not suitable for a large catalysis process. Therefore, to exploit the catalytic capability of the developed material, a multi-wire carbon-TMO is crucial.Here we report the LCVD technique's development to coat carbon nanofibers (CNF) mats with WO3-x for large-scale catalysis. We prepare the CNFs mats using the far-field electrospinning technique of Polyacrylonitrile/Dimethylformamide (PAN/DMF) solution followed by stabilization and carbonization. We have studied in detail the Joule heating of the CNFs mat, and we have developed a model allowing us to predict its temperature at a certain value of power dissipation used for a controlled chemical vapor deposition process. The deposited WO3-x films at the CNF mats are uniform, and the stoichiometry of the coating can be tuned by a post oxidation process or annealing in an inert atmosphere, yielding different catalytic behavior.[1] R. Wu, J. Zhang, Y. Shi, D. Liu, B. Zhang, Metallic WO2-carbon mesoporous nanowires as highly efficient electrocatalysts for hydrogen evolution reaction, J. Am. Chem. Soc. 137 (22) (2015) 6983-6986.[2] J. Chen, D. Yu, W. Liao, M. Zheng, L. Xiao, H. Zhu, M. Zhang, M. Du, J. Yao, WO3-x nanoplates grown on carbon nanofibers for an efficient electrocatalytic hydrogen evolution reaction, ACS Appl. Mater. Interfaces 8 (28) (2016) 18132-18139[3]Y. Lim, S. Kim, Y.M. Kwon, J.M. Baik, H. Shin, A highly sensitive gas-sensing platform based on a metal-oxide nanowire forest grown on a suspended carbon nanowire fabricated at a wafer level, Sens. Actuators B Chem. 260 (2018) 55-62.[4] Cisquella-Serra, A., Gamero-Castaño, M., Ferrer-Argemi, L., Wardini, J. & Madou, M. Controlled joule-heating of suspended glassy carbon wires for localized chemical vapor deposition. Carbon 156, 329–338 (2020)[5] L. Ferrer-Argemi, E.S. Aliabadi, A. Cisquella-Serra, A. Salazar, M. Madou, J. Lee, Size dependent electrical and thermal conductivities of electro-mechanically-spun glassy carbon wires, Carbon 130 (2018) 87-93.

Performance Improvement of Platinum-based Electrocatalyst Layer for PEFC by Mixing Single Walled Carbon Nanotubes

Performance Improvement of Platinum-based Electrocatalyst Layer for PEFC by Mixing Single Walled Carbon Nanotubes

A co-operative protection strategy to synthesize highly active and durable Fe/N co–doped carbon towards oxygen reduction reaction in Zn–air batteries

As promising alternatives to noble metal catalysts such as platinum-based electrocatalysts, Fe/N co–doped carbon (Fe–N–C) materials attract extensive attention because of their high activity and good durability. It is acknowledged that non–crystalline Fe–Nx moieties and crystalline iron–based nanoparticles as important active sites, largely determine the catalytic performance of Fe–N–C catalysts. However, the design and preparation of Fe–N–C catalyst still suffer from insufficient effective active sites because of the inevitable agglomeration phenomenon. In our work, from the perspective of minimizing catalyst size and prohibiting catalyst agglomeration, we put forward a co-operative protection strategy and successfully fabricate abundant Fe–Nx moieties and highly dispersed hyperfine Fe3C nanodots jointly decorated N–doped carbon framework (Fe–Nx/Fe3C@NC). By systematic characterization and analysis, we find the formation of these abundant active sites (Fe–Nx moieties and Fe3C nanodots) originates from the co-operative protection of different components in original precursors. As a result, the obtained product, Fe3C/Fe–Nx@NC hybrid displays high activity and robust durability towards oxygen reduction reaction (ORR) in both alkaline and acid medium. When employed as the cathode catalyst for Zn–air batteries, Fe3C/Fe–Nx@NC also exhibits comparable performance to that of commercial Pt/C catalyst. Clearly, our adopted strategy provides a good guidance on the preparation of high–performance transition metal–N–C–based catalysts for energy storage and conversion systems.

Synthesis and characterization of MWCNT-supported iron phthalocyanine catalyst for the treatment of wastepaper recycling mill wastewater using microbial fuel cell

This study reported that the preparation and characterization of multiwalled carbon nanotubes supported iron phthalocyanine (FePc/MWCNTs) composite catalyst and examined the treatment efficiency using wastepaper recycling mill wastewater in a microbial fuel cell (MFC). The MWCNTs were uniformly decorated over the FePc nano particles. The obtained catalyst was characterized using field emission scanning electron microscopy (FESEM), X-ray diffraction analysis, UV-visible spectrophotometry, energy-dispersive X-ray analysis (EDAX) Fourier-transform infrared spectroscopy (FTIR) analysis, BET analysis, Raman spectra, thermal gravimetric analysis (TGA), and X-ray photoelectron spectroscopy (XPS) analysis. In addition, the oxygen reduction reaction (ORR) of the catalyst has been investigated by cyclic voltammetry, linear sweep voltammetry analysis, and electrochemical impedance spectroscopy (EIS) analysis. There was an efficient removal of chemical oxygen demand (COD) with 87% and 0.650 W/m2 of power density achieved at 110 h of contact time. From this investigation, it is understood that the oxygen reduction reaction (ORR) of the FePc catalyst was improved by MWCNT supporting material. The obtained results suggested the excellent ORR activity of nanostructured FePc/MWCNTs as a promising alternative to conventional platinum-based electro catalyst for fuel cells.

On the Pathways of N-Doped Carbon Materials Active Sites During Oxygen Reduction Reaction

N-doped carbon materials have been considered as one of the most promising options for the replacement of platinum-based electrocatalysts towards the oxygen reduction reaction. However, what is known about this kind of catalysts and the identification of the active sites is still contradictory. Most of the scientific literature focuses on experimental characterization before ORR testing, leading to a consistent lack of knowledge about the surface chemistry at operando conditions. The development of operando techniques is, up to now, not enough to unravel with accuracy the reasons why these catalysts are as active as platinum-based electrodes and to understand the deactivation with time of use. In this work, the changes occurring in the active sites of N-doped carbon catalysts have been analysed in detail through pre- and post-ORR extended characterization of selectively N-doped carbon materials, along with sophisticated computational modelling.