Sulfur-Doped Graphene as an Efficient Metal-free Cathode Catalyst for Oxygen Reduction

The idea of doping carbon nanotubes (CNTs) with boron (B) and/or nitrogen (N) looks attractive in view of the changes brought in their electronic structures by the dopants. The field electron emission studies of boron (B) and nitrogen (N) doped CNTs grown in situ on pointed tungsten (W) tip and flat silicon (Si) substrate surfaces have been reported in this paper. The CNTs were grown by pyrolysis of ferrocene with suitable dopants. The morphology of the B-doped and N-doped CNTs on flat Si substrate was observed under SEM (Fig 1a & b). The B-doped CNTs on flat Si and pointed W tip have rope like structure and are also found to be considerably long (/spl sim/50 /spl mu/m). This may be attributed to the dopant atoms of boron, which act as catalysts for further growth of the CNTs along the tube axis. N-doped CNTs were, however, short (/spl sim/5 /spl mu/m), uniform and very densely packed. The Fowler-Nordheim (F-N) plots obtained from the I-V curves of doped field emitters show non-linear behavior (Fig 2 a and b). This non-linearity may be attributed to strong field penetration into the emitter apex region resulting into the local large variations of the electric field in the electron tunneling region. The local field enhancement factor (/spl beta/) and the current density (J) have been calculated from the slopes of the F-N plots. Field emission micrographs from the B- and N- doped CNTs on W tips reveal geometrical structures, typical of CNT bundles. The FEM images corresponding to B and N-doped CNTs on flat Si substrates show streaky structures. Typical field emission currents upto 200 /spl mu/A drawn from both B and N-doped CNTs are remarkably stable over periods greater than 3 hours (Fig 3 a and b). But in case of B-doped CNTs on flat Si, the set current of 400 /spl mu/A decreases slowly for about an hour and then gets stabilised at 300 /spl mu/A. The turn-on voltage to draw 0.1 nA current was found to be 3.32 kV for B-doped CNTs/W tip and 3.0 kV for B-doped CNTs /Si flat substrate. The threshold voltage to draw 1 /spl mu/A current was found to be 5.52 kV for B-doped CNTs/W tip and 4.6 kV for CNTs/Si flat substrate. For N-doped CNTs, the turn-on voltage to draw 0.1 nA current was found to be 3.12 kV for W tip and 3.88 kV for Si flat substrate. The threshold voltage to draw 1 /spl mu/A current was found to be 4.8 kV for N-doped CNTs/W tip and 7.0 kV for N-doped CNTs/Si flat substrate. So a lower voltage is needed to draw a fixed emission current from B-doped CNTs/Si than B-doped CNTs/W tip substrate, whereas a lower voltage is needed to draw a fixed emission current from N-doped CNTs/W tip than N-doped CNTs/Si substrates. Thus, it can be inferred from this study that the B-doped CNTs are better suited for large-area emitter applications such as flat panel display devices whereas the N-doped CNTs on pointed W tips would be promising candidates for high current density single electron beam applications.

The development of mixture, alloy, and core-shell nanocatalysts with nanomaterial supports for energy conversion in low-temperature fuel cells

The development of novel catalyst materials for oxygen reduction reaction (ORR) is one of the key topics in fuel cell research. In order to replace expensive noble-metal based catalysts that have been primarily employed as cathode catalysts in low-temperature fuel cells, different carbon-based materials that possess lower price, better availability and improved chemical stability have been investigated. An attractive approach is to employ nitrogen-containing carbon nanomaterials for this purpose 1-3. In this work the electrochemical reduction of oxygen has been studied on nitrogen-doped carbon nanomaterials modified glassy carbon (GC) electrodes. N-doped carbon nanotubes (N-CNT) and N-doped few-layer graphene/carbon nanotube (N-FLG/CNT) composite materials were investigated as catalyst materials. Dicyandiamide (DCDA) was used as nitrogen precursor for nitrogen doping of carbon nanomaterials. The doping was achieved by pyrolysing nanocarbon materials in the presence of DCDA at 800 °C. The CNT or FLG/CNT-to-nitrogen precursor mass ratio was 1:20. Electrochemical experiments were carried out in 0.1 M KOH using the rotating disk electrode (RDE) method. GC electrodes were modified using carbon nanomaterial suspension in isopropanol in the presence of Fuma-Tech FAA3 ionomer. The fuel cell performance of N-doped carbon materials was investigated by fabricating membrane-electrode assemblies (MEAs) using Fuma-Tech FAA3 membrane and for comparison purposes a commercial Pt/C catalyst was used as cathode material. The RDE experiments showed extraordinary electrocatalytic activity of N-doped carbon nanomaterials toward the ORR in alkaline media. A comparative study of direct methanol alkaline fuel cell performance was also performed. The power density curves are presented in Fig. 1. The MEAs with N-CNT, N-FLG/CNT and commercial 60% Pt/C cathode catalysts had power densities of 0.92, 0.72 and 0.72 mW cm−2 respectively, using methanol as fuel on anode side and pure O2 gas on cathode side. The results obtained in this work show that N-FLG/CNT and N-CNT catalysts possess excellent ORR activity in alkaline media and could be used as alternative cathode catalysts in alkaline anion-exchange membrane fuel cells.

Preface. List of Contributors. 1 Direct Methanol Fuel Cells: History, Status and Perspectives ( Antonino Salvatore Arico, Vincenzo Baglio, and Vincenzo Antonucci). 1.1 Introduction. 1.2 Concept of Direct Methanol Fuel Cells. 1.3 Historical Aspects of Direct Methanol Fuel Cell Development and State-of-the-Art. 1.4 Current Status of DMFC Technology for Different Fields of Application. References. 2 Nanostructured Electrocatalyst Synthesis: Fundamental and Methods ( Nitin C. Bagkar, Hao Ming Chen, Harshala Parab, and Ru-Shi Liu). 2.1 Introduction. 2.2 Fundamental Understanding of the Structure-Activity Relationship. 2.3 Synthetic Methods of Conventional Carbon-Supported Catalysts. 2.4 Synthetic Methods of Novel Unsupported Pt Nanostructures. 2.5 Conclusions. References. 3 Electrocatalyst Characterization and Activity Validation - Fundamentals and Methods ( Loka Subramanyam Sarma, Fadlilatul Taufany, and Bing-Joe Hwang). 3.1 Introduction. 3.2 Direct Methanol Fuel Cells - Role of Electrocatalysts. 3.3 Characterization Techniques for Anode and Cathode Catalysts. 3.4 Evaluation of Electrocatalyst Activity, Electrochemical Active Surface Area, Catalyst - Adsorbate Interactions, and Activity Validation Techniques. 3.5 Conclusions and Outlook. References. 4 Combinatorial and High Throughput Screening of DMFC Electrocatalysts ( Rongzhong Jiang and Deryn Chu). 4.1 Introduction. 4.2 Common Procedures for the Development of DMFC Catalysts. 4.3 General Methods for Combinatorial and High Throughput Screening. 4.4 Methods of Combinatorial Synthesis. 4.5 Electrode Arrays for High Throughput Screening. 4.6 Other Screening Methods for Catalyst Discovery. 4.7 Combinatorial Methods for DMFC Evaluation and Data Analysis. 4.8 Challenge and Perspective. References. 5 State-of-the-Art Electrocatalysts for Direct Methanol Fuel Cells ( Hanwei Lei, Paolina Atanassova, Yipeng Sun, and Berislav Blizanac). 5.1 Introduction. 5.2 Electrocatalysis and Electrocatalysts for DMFC. 5.3 DMFC Electrocatalyst Characterization and Evaluation. 5.4 DMFC Performance Advancement via MEA Design. 5.5 Prospects for DMFC. 5.6 Conclusions. References. 6 Platinum Alloys as Anode Catalysts for Direct Methanol Fuel Cells ( Ermete Antolini). 6.1 Introduction. 6.2 Phase Diagram vs. Activity: New Chances for DMFC Anodes. 6.3 Preparation Methods of Pt Alloys. 6.4 Activity Evaluation of Pt Alloys. 6.5 Stability of Pt-Ru Catalysts in DMFC Environment. 6.6 Conclusions. References. 7 Methanol-Tolerant Cathode Catalysts for DMFC ( Claude Lamy, Christophe Coutanceau, and Nicolas Alonso-Vante). 7.1 Introduction. 7.2 Thermodynamics and Kinetics of the Oxygen Reduction Reaction (ORR). 7.3 Experimental Details. 7.4 Synthesis and Characterizations of Nanostructured Catalysts for the ORR. 7.5 Catalyst Tolerance in the Presence of Methanol. 7.6 Summary and Outlook. References. 8 Carbon Nanotube-Supported Catalysts for the Direct Methanol Fuel Cell ( Chen-Hao Wang, Li-Chyong Chen, and Kuei-Hsien Chen). 8.1 Introduction. 8.2 Preparation of Carbon Nanotube-Supported Catalysts. 8.3 Characteristics of the Carbon Nanotube Electrode. 8.4 Electrochemical Behavior of Carbon Nanotube-Supported Catalysts. 8.5 Direct Growth of Carbon Nanotubes as Catalyst Supports. 8.6 Conclusion. References. 9 Mesoporous Carbon-Supported Catalysts for Direct Methanol Fuel Cells ( Chanho Pak, Ji Man Kim, and Hyuk Chang). 9.1 Introduction. 9.2 Mesoporous Carbon. 9.3 Mesoporous Carbon-Supported Catalyst. 9.4 Fuel Cell Performance of Mesoporous Carbon-Supported Catalyst. 9.5 Summary and Prospect. References. 10 Proton Exchange Membranes for Direct Methanol Fuel Cells ( Dae Sik Kim, Michael D. Guiver, and Yu Seung Kim). 10.1 Introduction. 10.2 Synthesis of Polymer Electrolyte Membranes for DMFC. 10.3 Conclusions. References. 11 Fabrication and Optimization of DMFC Catalyst Layers and Membrane Electrode Assemblies ( Liang Ma, Yunjie Huang, Ligang Feng, Wei Xing, and Jiujun Zhang). 11.1 Introduction. 11.2 Components for DMFC Catalyst Layer Optimization. 11.3 Catalyzed DMFC Electrode Structure and Fabrication Process. 11.4 Other Electrode Fabrication Methods for DMFCs. 11.5 Summary. References. 12 Local Current Distribution in Direct Methanol Fuel Cells ( Andrei A. Kulikovsky and Klaus Wippermann). 12.1 Introduction. 12.2 Model. 12.3 The Bifunctional Regime of DMFC Operation. 12.4 Direct Methanol-Hydrogen Fuel Cells (DMHFCs). 12.5 Bifunctional Activation of DMFC. 12.6 Conclusions. 12.7 List of symbols. References. 13 Electrocatalysis in the Direct Methanol Alkaline Fuel Cell ( Keith Scott and Eileen Yu). 13.1 Introduction. 13.2 History of Alkaline Methanol Fuel Cells. 13.3 Electrocatalysis of Methanol Oxidation in Alkaline Media. 13.4 Oxygen Reduction and Methanol Tolerant Electrocatalysts. 13.5 Direct Methanol Fuel Cells in Alkaline Media. 13.6 Direct Alkaline Polymer Electrolyte Membrane Fuel Cells. 13.7 Alkaline Fuel Cells with other Direct Liquid Fuels. 13.8 Conclusions. References. 14 Electrocatalysis in Other Direct Liquid Fuel Cells ( Sharon L. Blair and Wai Lung (Simon) Law). 14.1 Introduction. 14.2 Electrocatalysis of Direct Formic Acid Fuel Cells. 14.3 Electrocatalysis of Direct Ethanol Fuel Cells. 14.4 Electrocatalysis of Direct Hydrazine Fuel Cells. 14.5 Other Direct Liquid Fueled Fuel Cells. 14.6 Summary. References. Index.

Today, the development of active and stable catalysts still represents a challenge to be overcome in the research field of low-temperature fuel cells.[...]

In modern society, electrical energy is commonly converted by chemical energy, which is essential for various applications. Over time, several techniques involved in converting energy have been investigated, including electricity generator, battery, and fuel cell. Conventional electric generators powered by fossil fuel face challenges related to efficiency because of multiple steps within its energy converting process. On the other hand, batteries also have their limitations, primarily related to density of energies, which is limited by their volume for storing reactants. In contrast, fuel cells represent an anticipated technique for supplying power in the future. This innovative technique takes the strengths of both electricity generator and battery, offering great efficiency of converting energies process and impressive density of energies simultaneously. By directly converting the chemical energy from fuels into electrical energy through an electrochemical process, fuel cells overcome the efficiency and storage limitations associated with traditional generators and batteries. Microfluidic fuel cells (MFFCs) are a category of fuel cells with structure sizes ranging from 1 to 1000 μm. The choice of catalyst material has been demonstrated to affect the efficiency of MFFCs. In recent years, there has been growing interest in utilizing metal nanoparticle/ conductive polymer nanocomposites as catalysts in fuel cells. Conductive polymers have emerged as promising substitutes for traditional carbon-supported catalysts. Thanks to properties of large specific areas, satisfying electrically conductive capabilities, and chemically stable ability in their porous surfaces, it makes polymers attractive for supporting catalysts in fuel cells. When metal nanoparticles (NPs) are incorporated into these conductive polymers in a highly dispersed manner, it maximizes the active surface area available for oxidation and reduction reactions, thereby allowing for low catalyst loading in fuel cell applications. In this study, we aim to explore and discuss recent developments in the field of polymer-supported metal nanoparticles as catalysts for fuel cells. By examining the synergistic effects of conductive polymers and metal NPs, we hope to gain insights into their possibility to improve the efficiency and performance of fuel cell. This research could be an advancement and reference for developing more efficient and sustainable energy conversion technologies.

Polymer electrolyte membrane (PEM) fuel cells have been viewed as promising power source candidates for transport, stationary, and portable applications due to their high efficiency and low emissions. The platinum is the most commonly used catalyst material for the oxygen reduction reaction (ORR) at the cathode of PEM fuel cells; however, despite ample investigations being done on this type of catalyst, the performance and durability of platinum still need to be improved in order to meet the commercial target. The material on which the catalyst is supported is important for the high dispersion and narrow distribution of Pt nanoparticles, and these characteristics are closely related to electrocatalytic activity of the catalysts. The support materials can influence the catalytic activity by interplaying with catalytic metals, and the durability of the catalyst is also greatly dependent on its supports.Graphene has recently emerged as a highly promising catalyst support material for PEMFC applications owing to its immense surface areas, along with excellent conductivity and electron transfer capabilities that are important criteria pertaining to electro-catalysis. Graphene is theoretically composed of only graphitic carbon atoms which can provide added resilience against carbon corrosion during PEMFC operation, although the relatively inert and hydrophobic nature of its surface does not culminate in facile Pt deposition, requiring functionalization procedures to obtain well dispersed nanoparticles and overcome stability limitations. To this end, nitrogen doped graphene and other graphitic carbons have been extensively developed and investigated for fuel cell catalyst applications, either as stand-alone ORR electrocatalysts in alkaline media as Pt nanoparticle supports under acidic (i.e. PEMFC) conditions. The presence of nitrogen dopants has been reported to exert a “tethering” effect on Pt nanoparticles, providing both beneficial catalyst activity and stability enhancements. While density functional theory simulations exist in the literature investigating the adsorption and binding interactions between Pt and either nitrogen and boron doped graphene or carbon nanotubes (CNTs), there exists an overall lack of fundamental understanding regarding the Pt-heteroatom doped graphene catalyst-support interactions and their associated impact on ORR performance and operational stability. Furthermore, the impact of graphene doped with various other heteroatoms (i.e. sulfur) remains largely unexplored despite their high potential for applications as ORR catalysts or catalyst support materials. Elucidation of these important considerations can be provided by effectively linking fundamental computational simulations with detailed experimental investigations.In the present work, we report the development of sulfur-doped graphene (SG) by thermal shock/quench annealing a mixture of graphene oxide (GO) and phenyl disulfide (PDS). These materials were used as Pt nanoparticle support materials, whereby after Pt deposition onto SG (Pt/SG) by a modified ethylene glycol (EG) method, uniformly sized nanoparticles well dispersed across the entirety of the SG surface were successfully obtained. Improved ORR activity was found for Pt/SG in comparison to Pt supported on un-doped graphene (Pt/G) along with commercial state of the art Pt/C (Figure 1). Furthermore and most notably, we also observed significantly enhanced stability of Pt/SG (Figure 1).On the basis of these observations, we performed ab initio density functional theory calculations to investigate the interactions occurring between SG and Pt and elucidate the root causes of ORR performance and stability enhancements. We found that the strengthened interaction and binding energies between Pt and SG arose, and could exclusively be linked to sulfur incorporation based on comparative investigations with un-doped G. Specifically, sulfur doping led to stronger adsorptive and cohesive binding energies with Pt, leading to the aforementioned catalyst-support tethering effect, along with negatively shifting the d-band center of the Pt atoms. These findings were used to explain the dramatically enhanced stability and improved activity of Pt/SG, respectively, in comparison to both Pt/G and Pt/C. This work represents the first comprehensive report of fundamental ab initio simulations linked to rigorous experimental investigations for sulfur doped graphene, and furthermore Pt/SG is presented for the first time as a highly active ORR catalyst with exemplary stability for PEMFC applications.

Structural, electronic properties, and quantum capacitance of B, N and P-doped armchair carbon nanotubes

The direct oxidation of hydrocarbons in the fuel cell has attracted increasing interest as a power source for portable applications as compared to that fed with hydrogen fuel. Hydrocarbons such as methanol, ethanol, ethylene glycol, and glucose exhibit high volumetric energy density, easy storing and delivery system, renewable in nature and are economically and environmentally friendly as compared to hydrogen fuel. Based on the oxidation of the hydrocarbons directly in the fuel cell, they are termed as the direct methanol fuel cell (DMFC), direct ethanol fuel cell (DEFC), direct ethylene glycol fuel cell (DEGFC), and direct glucose fuel cell (DGFC), which are discussed in the chapter. The performance of these fuel cell is better in alkaline electrolyte than that in the acid electrolyte at low temperature (25 °C) and are fascinating owing to use of low-cost alkaline exchange membrane, non-platinum catalyst, no fuel crossover and low CO poisoning. The anode catalysts such as noble (Pt, Ru, Pd) and non-noble metals (Co, Ni), binary and ternary alloys (PtRu, PtPdRu, PdBiRu, PdPtCo), oxides (PdCeO2, PdNiO), different nanostructures (Pd@Pt) developed for direct oxidation of the hydrocarbons in the presence of different forms of support such as functionalised carbon nanotubes, graphene, metal (N, P, B) doped graphene, ordered mesoporous carbon in alkaline medium at low temperature are discussed. Recent development in the alkaline fuel cell using methanol, ethanol, ethylene glycol and glucose directly as fuel and various anode catalysts with the corresponding reaction mechanism in fuel oxidation in alkaline medium is elaborated. The best performance is achieved in a typical DMFC using PtRu as anode catalyst with maximum peak power density of 168 mW cm−2 in alkaline medium. The performance of Pd based binary and ternary catalysts are much superior to Pt-based catalysts in DEFC, DEGFC, and DGFC in alkaline medium. A DEFC using PdNi/C as anode catalyst, a cation exchange membrane as electrolyte membrane shows peak power density of 360 mW cm−2, a DEGFC using PdNi/C as anode catalyst, KOH doped PBI membrane as electrolyte membrane gives peak power density of 112 mW cm−2 and a DGFC using PdNi/C as anode catalyst, Tokuyama A201 as anion exchange membrane electrolyte demonstrates peak power density of 38 mW.cm−2. The chapter also includes the detailed comparison of cell parameters (fuel concentration, fuel flow rate, catalyst loading, operating temperature etc.), cell performance, current-voltage characteristics, stability and durability of the alkaline fuel cell using methanol, ethanol, ethylene glycol and glucose as fuel.

Fe/N/C is a promising electrocatalyst for oxygen reduction reaction (ORR). This type catalyst can perform in both acidic and alkaline media. In acidic media, the active sites of Fe/N/C can be corroded; however, in alkaline media, Fe/N/C can exhibit high stability. Therefore, it is promising to explore the applications of Fe/N/C catalyst in alkaline fuel cell. Herein, we will talk about our recent advances in preparation of Fe/N/C catalysts and the application of them in alkaline fuel cells: (1) By using 2-aminothiazole, a molecule containing both N and S atoms, we prepared S co-doped Fe/N/C catalyst with graphene nanosheets. In alkaline solution, this catalyst exhibited high ORR activity with half-wave potential of 0.926 V and mass activity of 0.56 A g-1 @ 1.0 V. Furthermore, the catalyst displayed excellent durability, and only lost 9% of initial activity after 100 h of durability test at 0.80 V. In alkaline anion exchange membrane fuel cell (AEMFC) test, the peak power density could reach 164 mW cm−2. (2) We used the unzipped carbon nanotubes as carbon support and melamine as nitrogen source, and prepared a Fe/N/C catalyst with high ORR activity in alkaline media. The edge sites of unzipped carbon nanotubes play a key role for high catalyst activity. (3) we explored a series of nitrogen source including binary polymer of melamine-terethalaldehyde, ternary polymer of cynuric acid, 2, 4-diamino-6-phenyl-1, 3, 5-triazine, and melamine. N-doped carbon nanotubes with encapsulated Fe nanoparticles were prepared. The catalyst exhibited considerably high ORR activity in alkaline solution. We further tested its performance in alkaline membrane direct ethanol fuel cell, and the peak power density was about 64 mW cm-2. These results demonstrated that Fe/N/C is a promising candidate for ORR electrocatalyst in alkaline fuel cell.

Surmounting the sluggish oxygen reduction reaction (ORR) kinetics in developing the metal-free cathode catalyst for fuel cell, carbon nanomaterials with heteroatoms doped intended to focus vigorously. Electronegativity difference between heteroatoms is prone to maximize the C-C bond polarization to generate ORR active sites. The current work emphasizes on synergistic effect of nitrogen, sulfur and fluorine tri-doped porous carbon toward potential ORR catalyst. Pyrolysis of sulfonated-polyaniline supported on Ketjenblack (KB) in presence of NH4F turns into N-S-F tri-doped catalyst. F tri-doping creates more active sites through inducing maximum charge polarization/spin density alterations which are promising for ORR improvement. ORR activity of doped catalysts is examined by rotating ring disk electrode in both acidic and alkaline media with dominant four electron transfer. The Enhanced activity with superior stability, CH3OH sensitivity and CO susceptibility of the developed N-S-F/KB catalyst finds suitable application in polymer electrolyte membrane fuel cell (PEMFC). The peak power densities of 7.3 and 24 mW cm−2 in alkaline and acidic medium respectively are obtained in the PEMFCs using this catalyst. Demonstration of a tri-doped N, S, F catalyst toward ORR and its fuel cell performance studies in acidic and alkaline media is the first of its kind in the literature.

Existing energy sources based on fossil fuel is an obstacle for environmental sustainability, and there is a concern regarding the depletion of fossil fuel resources [1], [2]. Therefore, it is essential to develop new alternative energy sources. As a safe and effective method of generating power, the conversion of natural biomass to electricity in the form of direct biomass fuel cell (DBFC) has attracted significant attention due to its high efficiency and low emissions [3]. Among various DBFCs, direct urea fuel cell (DUFC) using urea in wastewater and urine as fuel has recently been validated as a clean energy device [4]. The overall power response of the DUFC mainly depends on the urea oxidation reaction (UOR), so it is vital to investigate the UOR catalysts. Ni-based catalysts, which are inexpensive and commonly used as UOR catalysts, have widely utilized for replacement of noble metals. The Ni/C electrode as an anode in the reported study achieved a power density of 1.7 mW/cm2 [5], and nanostructured Ni-based catalysts or bimetallic types of catalysts also have been implemented for better performances [6], [7]. However, the above studies proceeded in an alkaline medium, which makes it difficult to use actual wastewater or urine directly as a source for fuel cells application. Since the electrochemical features of nickel-based catalysts are based on the mechanism of electrooxidation from Ni2+ to Ni3+ in alkaline medium, the catalytic activity in neutral solutions is less well distinguished [8]. Thus, nickel-based catalysts essentially comprising Ni3+ ions will more efficiently improve the UOR performances even if a neutral atmosphere of urea solution is adopted. In this study, the catalyst with a nanostructures array based on nickel oxyhydroxide with metal (metal-NiOOH) was prepared by using the electrospinning process for DUFC. The morphology and the structure of the metal-NiOOH catalysts were observed using scanning electron microscopy, Transmission electron microscopy, and X-ray diffraction methods. The metal-NiOOH catalyst used as the DUFC anode showed excellent UOR performances and power achievements in real human urine. A comprehensive investigation on the performances of metal-NiOOH and the function of internal Ni3+ ions as a catalyst in DUFC will be presented. References Suranovic, Steven. "Fossil fuel addiction and the implications for climate change policy." Global Environmental Change 23.3 (2013): 598-608. Veziroğlu, T. Nejat, and Sümer Şahi. "21st Century’s energy: Hydrogen energy system." Energy conversion and management 49.7 (2008): 1820-1831. Zhao, Xuebing, and J. Y. Zhu. "Efficient conversion of lignin to electricity using a novel direct biomass fuel cell mediated by polyoxometalates at low temperatures." ChemSusChem 9.2 (2016): 197-207. Xu, Wei, et al. "Nickel-cobalt bimetallic anode catalysts for direct urea fuel cell." Scientific reports 4 (2014): 5863. Lan, Rong, Shanwen Tao, and John TS Irvine. "A direct urea fuel cell–power from fertiliser and waste." Energy & Environmental Science 3.4 (2010): 438-441. Ye, Ke, et al. "Facile preparation of three-dimensional Ni (OH) 2/Ni foam anode with low cost and its application in a direct urea fuel cell." New Journal of Chemistry 40.10 (2016): 8673-8680. Guo, Fen, et al. "Preparation of nickel-cobalt nanowire arrays anode electro-catalyst and its application in direct urea/hydrogen peroxide fuel cell." Electrochimica Acta 199 (2016): 290-296. Vedharathinam, Vedasri, and Gerardine G. Botte. "Direct evidence of the mechanism for the electro-oxidation of urea on Ni (OH) 2 catalyst in alkaline medium." Electrochimica Acta 108 (2013): 660-665. Acknowledgement This work was supported by Agency for Defense Development (ADD) as global cooperative research for high performance and light weight bio-urine based fuel cell (UD160050BD) and the Ocean University of China-Auburn University (OUC-AU) Grants program.

Extensive use of non-renewable energy sources and excessive accumulation of hard-to-recycle waste, such as end-of-life tires, are among the most significant environmental problems today. For a more sustainable future, it is essential to find alternative solutions to energy and special waste management. For example, waste tires can be used to synthesize high-tech porous carbon materials, which can be used as a carbon support in fuel cell catalysts. [1] While fuel cells offer a promising alternative to some fossil fuel-based technologies, low temperature fuel cell catalysts rely on expensive platinum. Non-platinum-group metal (NPGM) catalysts, such as iron and nitrogen co-doped carbon materials are good contenders to platinum-based catalysts for the oxygen reduction reaction. Synthesizing porous carbon materials for more economically viable NPGM fuel cell catalysts could provide one way to use waste tires more sustainably and lower the cost of efficient fuel cell catalysts.For this work, a carbon material was synthesized by pyrolyzing tire granules (Imdex A/S) at 1000 °C for three hours in Ar [2]. Based on this carbon material, several iron and nitrogen co-doped catalyst materials were synthesized using Fe(NO3)3 as the iron source, dicyandiamide or guanidine as the nitrogen source, and ZnCl2 as a pore modifier. All synthesized materials were acid washed overnight to remove redundant elements such as Zn from the pore modifier and various impurities originating from the tire granules (mainly Si, S, Ca, and Zn). Finally, the materials pyrolyzed for a second time. The pyrolysis temperature, choice of nitrogen compound, and precursor ratios were varied for the syntheses described in this work.The NPGM catalyst materials were characterized by various physical and electrochemical methods to describe the relationship between the catalyst structure and the activity of the oxygen reduction reaction. SEM and SEM-EDX were used to evaluate the morphology and composition of the catalyst materials. N2 sorption data suggested that the specific surface area ranged from 77 to 194 m2 g-1 for all materials. Electrochemical characterization was performed in 0.1M KOH solution using the rotating disk electrode method. The highest onset potential (Eon = 920 mV vs RHE) was reached by a material using guanidine as the nitrogen source pyrolyzed at 900 °C, which is comparable to other recently described NPGM materials [3], including waste-tire derived NPGM catalysts [4]. Acknowledgements: This work was supported by the following projects: PRG676 “ Development of express analysis methods for micro-mesoporous materials for Estonian peat derived carbon supercapacitors” (1.01.2020- 31.12.2024)"Advanced materials and high-technology devices for sustainable energetics, sensorics and nanoelectronics” (TK141) (1.01.2016−1.03.2023) References [1] J. S. Gnanaraj et al., Sustainability 10(8), 2840 (2018)[2] J. Laanemäe, R. Jäger, P. Teppor, O. Volobujeva, and Enn Lust, ECS Transactions, 108, p. 39 (2022)[3] R. Gutru et al., International Journal of Hydrogen Energy, 47 (2022)[4] M. Muhyuddin et al., Electrochemica Acta, 433, 141254 (2022)

Co nanoparticles and ZnS decorated N, S co-doped carbon nanotubes as an efficient oxygen reduction catalyst in zinc-air batteries

Boron and oxygen-codoped porous carbon as efficient oxygen reduction catalysts