Materials For Oxygen Reduction Reaction Research Articles

Electrocatalytic reduction of oxygen on Co3O4: Effects of processing method

In this study, cathode materials for oxygen reduction reaction were produced. Co3O4 spinel oxides were synthesized by hydrazine based precursor method. X-ray appearing for 311 plane and lattice parameter a = 8.06 Å diffraction pattern showed cubic crystalline structure with 100% relative intensity. These oxides were supported on vulcan carbon by in situ precursor method and by manually grinding in agate mortar and pestle. Prepared Co3O4/C electrodes were characterized by SEM/EDAX to understand the surface morphology. The electrochemical measurements were made using cyclic voltammetry and steady-state polarization techniques. Oxygen reduction reaction was studied in alkaline solution (6 M KOH) by using Hg/HgO, OH− as the reference electrode. The results have shown lower activity for the ORR on the Co3O4/C species compared to that on Pt/C, but higher activity compared to that of pure vulcan carbon. It is observed that oxygen reduction proceeds via 4 electron transfer for Co3O4/C obtained by photocatalytic decomposition.

Laser-Induced Graphene.

Research on graphene abounds, from fundamental science to device applications. In pursuit of complementary morphologies, formation of graphene foams is often preferred over the native two-dimensional (2D) forms due to the higher available area. Graphene foams have been successfully prepared by several routes including chemical vapor deposition (CVD) methods and by wet-chemical approaches. For these methods, one often needs either high temperature furnaces and highly pure gases or large amounts of strong acids and oxidants. In 2014, using a commercial laser scribing system as found in most machine shops, a direct lasing of polyimide (PI) plastic films in the air converted the PI into 3D porous graphene, a material termed laser-induced graphene (LIG). This is a one-step method without the need for high-temperature reaction conditions, solvent, or subsequent treatments, and it affords graphene with many five-and seven-membered rings. With such an atomic arrangement, one might call LIG "kinetic graphene" since there is no annealing in the process that causes the rearrangement to the preferred all-six-membered-ring form. In this Account, we will first introduce the approaches that have been developed for making LIG and to control the morphology as either porous sheets or fibrils, and to control porosity, composition, and surface properties. The surfaces can be varied from being either superhydrophilic with a 0° contact angle with water to being superhydrophobic having >150° contact angle with water. While it was initially thought that the LIG process could only be performed on PI, it was later shown that a host of other polymeric substrates, nonpolymers, metal/plastic composites, and biodegradable and naturally occurring materials and foods could be used as platforms for generating LIG. Methods of preparation include roll-to-roll production for fabrication of in-plane electronics and two different 3D printing (additive manufacturing) routes to specific shapes of LIG monoliths using both laminated object manufacturing and powder bed fabrication methods. Use of the LIG in devices is performed very simply. This is showcased with high performance supercapacitors, fuel cell materials for oxygen reduction reactions, water splitting for both hydrogen and oxygen evolution reactions coming from the same plastic sheet, sensor devices, oil/water purification platforms, and finally applications in both passive and active biofilm inhibitors. So the ease of formation of LIG, its simple scale-up, and its utility for a range of applications highlights the easy transition of this substrate-bound graphene foam into commercial device platforms.

Formation of N‐rich Hierarchically Porous Carbon via Direct Growth ZIF‐8 on C3N4 Nanosheet with Enhancing Electrochemical Performance

AbstractPresented here are the synthesis of series N‐rich hierarchically porous carbons via disposition of ZIF‐8 on g‐C3N4 nanosheets and their uses as electrode materials in oxygen reduction reaction (ORR) and supercapacitor. Electron microscopy images show the successful formation of 2D carbon structures through using layered C3N4 as a novel template and ZIF‐8 as carbon precursor. The meso and macropores of the ZIF‐8 derived carbons are significantly developed with g‐C3N4 incorporation. Electrochemical measurements demonstrate that the resulting 2D carbons exhibit enhancing performance of supercapacitance up to 159.0 F/g at a current density of 1 A/g, meanwhile the optimized electrocatalytic activity for ORR in O2 saturated 0.1 M KOH electrolyte, with a distinct oxygen reduction peak at 0.71 V that was comparable to the value of the referenced Pt/C catalyst. Notably, this is the first investigation of layered g‐C3N4 supported ZIF‐8 derived carbons for ORR and supercapacitance. This work may offer a new way to prepare novel electrocatalysts by effective integration of ZIF‐8 derived carbon and the g‐C3N4 skeleton.

Probing the correlation between Pt-support interaction and oxygen reduction reaction activity in mesoporous carbon materials modified with Pt-N active sites

Pt nanoparticles (NPs) on nitrogen-functionalized mesoporous carbon have proved to be interesting materials for oxygen reduction reaction. In this paper, we employed a new synthetic route to simultaneously deposit Pt NPs and introduce N-doping in the carbon support, by using dichloro(1,10-phenanthroline)platinum(II) or dichloro(2,2′-bipyridyl)platinum(II) as a precursor of both platinum and nitrogen. Pt NPs (average size 2.5 nm) were successfully synthesized by solid state reduction of Pt(II) under N2/H2 flow at 650 °C on a commercial mesoporous carbon. The synthesis was also carried out by employing PtCl2 or Pt(acac)2 as platinum precursors and 1,10-phenanthroline or 2,2′-bipyridyl as nitrogen dopant agents and the resulting materials were taken for comparison. XPS analysis confirmed that during the thermal treatment the ligand degrades and the nitrogen is embedded in the mesoporous carbon structure, resulting in a surface modification of the carbon support with preservation of bulk conductivity and thermal stability. Electrochemical characterization at a rotating disk electrode in O2-saturated 0.1 M HClO4 revealed a superior catalytic activity for ORR, in terms of E1/2 and mass activity, in those catalysts showing higher PtN interaction, expressed as binding energy shift of nitrogen components. Furthermore, cyclic voltammetry analysis in Ar purged 0.1 M HClO4 electrolyte showed that nitrogen doping appears to inhibit PtO formation. The influence of nitrogen incorporation in the carbon matrix on Pt NPs/support interaction was also rationalized on the basis of density functional theory simulations.

Nitrogen Doped Graphene-Carbon Nanotubes and Nitrogen Doped Nano-Onion Hybrids As High-Performance Catalysts for Oxygen Reduction Reaction

A nitrogen doped nanoonion and nitrogen doped graphene-carbon nanotube hybrid (NNO/NG-NCNT) was prepared as a non-precious electrocatalytic material for oxygen reduction reaction (ORR). The nitrogen doped nanooion (NNO) is a new promising carbon-based catalytic material, and its electrocatalytic activity toward ORR was further improved by mixing with nitrogen doped graphene-CNT (NG-NCNT). This improvement was achieved through the formation of hybrid structure, because the NG-NCNT weakened aggregation of the NNO by working as spacers. The formation of the NNO/NG-NCNT was characterized by Raman spectroscopy, field emission scanning electron microscopy, high resolution transmission electron microscopy and X-ray photoelectron spectroscopy. The ORR performance of the NNO/NG-NCNT was studied using rotating disk electrode (RDE) measurement. The RDE results indicated that the NNO had higher ORR activity than that of NG/NCNT, and the NNO/NG-NCNT showed superior ORR performance which was comparable to that of the platinum-based catalyst. In addition, the NNO/NG-NCNT has excellent long-term durability and tolerance to methanol crossover effect. Thus, the high electrocatalytic activity and good stability of the NNO/NG-NCNT make its potential applications as a metal-free catalyst for ORR.

In Situ Generated Dual-Template Method for Fe/N/S Co-Doped Hierarchically Porous Honeycomb Carbon for High-Performance Oxygen Reduction.

Heteroatoms doping is able to produce catalytic sites in carbon materials for oxygen reduction reaction (ORR); while hierarchically porous structure is necessary for efficient exposure and accessibility of the usually limited catalytic sites in such activated carbon catalysts. This work reports an in situ generated dual-template method to synthesize the Fe/N/S co-doped hierarchically porous carbon (FeNS/HPC), with NaCl crystallites formed during the precursor lyophilization process as the primary template to generate ∼500 nm macropores with ultrathin graphene-like carbon-layer walls, and Fe3O4 nanoparticles formed during the high-temperature carbonization process as the secondary template to produce mesopores on the walls of macropores. As well as the coexistence of graphitic-N, pyridinic-N, and thiophene-S which are beneficial to ORR, the as prepared FeNS/HPC possesses a highly graphitized and interconnected hierarchical porous structure, giving a specific surface area as high as 938 m2 g-1. As a consequence, it exhibits excellent four-electron oxygen reduction performance in both alkaline and acid electrolytes. The in situ generation and facile solution removal make the present template method a promising way for scale-up preparation of active porous carbon materials for various applications.

Coral-like Co3O4 Decorated N-doped Carbon Particles as active Materials for Oxygen Reduction Reaction and Supercapacitor

Coral reef has a unique dendritic structure with large specific surface area, rich pore structure, so that it can be attached to a large number of zooxanthellae for gas exchange. Coral reef ecosystems are also known as underwater rainforests. Inspired by this biological structure, we designed and fabricated coral-like Co3O4 decorated N-doped carbon particles (Co3O4/N-CP). The obtained Co3O4/N-CP-900 catalyst shows efficient ORR electrocatalytic performances in an alkaline medium with a positive onset and half-wave potentials of 0.97 and 0.90 V (vs. RHE), as well as a high diffusion-limited current density (5.50 mA cm−2) comparable to that of a Pt/C catalyst (5.15 mA cm−2). It also displays better stability and methanol tolerance than commercial Pt/C. In addition, the Co3O4/N-CP-900 electrode has a high specific capacitance of 316.2 F g−1 in 6 M KOH, as well as good rate capabilities and excellent cycle performance. These results are due to large surface area, narrow pore size distribution, high density electrochemical energy conversion and storage activity centers. This method presented here offers an effective path for the development of high performance multi-functional carbon-based materials for ORR and supercapacitor applications.

Halloysite-derived nitrogen doped carbon electrocatalysts for anion exchange membrane fuel cells

Developing the low-cost, highly active carbonaceous materials for oxygen reduction reaction (ORR) catalysts has been a high-priority research direction for durable fuel cells. In this paper, two novel N-doped carbonaceous materials with flaky and rod-like morphology using the natural halloysite as template are obtained from urea nitrogen source as well as glucose (denoted as GU) and furfural (denoted as FU) carbon precursors, respectively, which can be directly applied as metal-free electrocatalysts for ORR in alkaline electrolyte. Importantly, compared with a benchmark Pt/C (20wt%) catalyst, the as-prepared carbon catalysts demonstrate higher retention in diffusion limiting current density (after 3000 cycles) and enhanced methanol tolerances with only 50-60mV negative shift in half-wave potentials. In addition, electrocatalytic activity, durability and methanol tolerant capability of the two N-doped carbon catalysts are systematically evaluated, and the underneath reasons of the outperformance of rod-like catalysts over the flaky are revealed. At last, the produced carbonaceous catalysts are also used as cathodes in the single cell H2/O2 anion exchange membrane fuel cell (AEMFC), in which the rod-like FU delivers a peak power density as high as 703 mW cm−2 (vs. 1106 mW cm−2 with a Pt/C benchmark cathode catalyst).

A new facile approach to prepare reduced graphene oxide and MoO2/reduced graphene oxide as electrode materials for oxygen reduction reactions

A facile one-pot method for the formation of MoO2/RGO has been established using Mo particles as both the reductant for graphene oxide (GO) and as the Mo source. The Mo powder efficiently reduced the GO under acidic conditions to give reduced GO (RGO) and Mo ions. These ions were then transformed into MoO2 and MoO2/RGO composites were formed by tuning the pH of the solution. Other variables such as reaction time and Mo:GO weight ratio were also investigated. The MoO2/RGO composite prepared at 3:1 (Mo:GO, called MoO2/RGO3) had the best electrochemical performance for the oxygen reduction reaction (ORR) in alkaline medium. The ORR reaction at the MoO2/RGO3 electrode mainly proceeded via a four-electron pathway and the electrode displayed superior catalytic activity and good stability. These results indicate that MoO2/RGO3 could be a promising noble metal-free electrocatalyst for fuel cells.

Scalable preparation of sized-controlled Co-N-C electrocatalyst for efficient oxygen reduction reaction

Heat-treated metal-nitrogen-carbon (M-N-C) materials are emerging as promising non-precious catalysts to replace expensive Pt-based materials for oxygen reduction reaction (ORR) in energy conversion and storage devices. Despite recent progress, their activity and durability are still far from satisfactory. The activity site and particle size are among the most important factors for the ORR activity of M-N-C catalysts. Extensive efforts have been made to reveal the correlation of active site and activity. However, it remains unclear to what extent the particle size will influence the ORR activity of M-N-C materials. Moreover, to the best of our knowledge, controllable synthesis of M-N-C catalysts with high-density activity sites remains elusive. Herein, we develop a straightforward method to produce a monodisperse and size-controlled Co-N-C (Nano-P-ZIF-67) electrocatalyst, and systemically investigate its catalytic mechanisms. Only by optimizing the particle size, Nano-P-ZIF-67 outperforms the commercial 20 wt% Pt/C regarding all evaluating indicators for ORR catalysts in alkaline media including higher catalytic activity, durability, and stronger methanol tolerance. Nano-P-ZIF-67 is assembled into a cell, and the cell shows a power density of 45.5 mW/cm2, which is the highest value among currently studied cathode catalysts. We expect Nano-P-ZIF-67 to be a highly interesting candidate for the next generation of ORR catalysts.

The key roles of trace iron for nitrogen, sulfur dual-doped carbon nanospheres as high efficient oxygen reduction catalyst

Trace iron (Fe) has been found to be critical for improving the catalytic activity of heteroatom-doped carbon materials for oxygen reduction reaction (ORR). However, the exact roles played by the trace Fe in the catalysts have not been studied in detail. In this study, nitrogen (N) and sulfur (S) dual-doped carbon nanospheres were synthesized with and without trace Fe addition, named NSFeDC and NSDC, respectively. NSFeDC showed obviously stronger catalytic activity for ORR than NSDC. The microstructures of these two catalysts were characterized comprehensively. After adding the trace Fe, the contents of N and S in NSFeDC were 8.1 and 3.3 times higher than those in NSDC. The functional group composition analysis demonstrated that one part of the increased N/S formed the chemical bond of Fe–N and Fe–S, and the other part was involved in the abundant extra formation of metal-free N/S-based active site, such as pyridinic N and –C–S–C–. The underlying mechanism is that the trace iron not only participated itself in constructing the active sites, but also served as the catalyst for the formation of N/S-based active sites. The comparison between the TEM images of NSDC and NSFeDC clearly showed that the size of the nanosphere increased after adding the trace Fe. This was probably because the iron atom connected two separate carbon groups together by bonding with the nitrogen atoms. Besides the enlarged particle size, the surface area of NSFeDC decreased by nearly one half compared to that of NSDC.

Observation of Oxygen Binding on PGM-Free Electrocatalysts By Ambient Pressure XPS and XAS

The most promising class of PGM-free materials for oxygen reduction reaction (ORR) is based on graphene-like carbon containing nitrogen and transition metal (MNC). They show promise as replacement of Pt in two different technological platforms - alkaline exchange membrane fuel cells (AEMFCs) and proton exchange membrane fuel cells (PEMFC). [1-3] It is well established that nitrogen coordination with metal in the carbon network of MNC materials is directly related to ORR activity; however, the exact nature of the active sites is still debated even after over 50 years of research. Understanding the specific roles of nitrogen and metal in the properties/activity/stability/durability of MNC-based catalytic materials is a prerequisite for the rational design of ORR electrocatalysts with improved performance. The key component in elucidating the relationship between the chemistry of active sites and activity is a better understanding of the formation of adsorbates, intermediates, and products during reactions occurring within the fuel cell. In situ monitoring reaction steps under realistic conditions in metal-free and metal-containing building blocks will shed light onto the reaction mechanism that is essential for developing active and durable PGM-free catalyst for ORR. [4] We will report on AP-XPS analysis for series of electrocatalysts belonging to Fe-N-carbon families based on sacrificial support method (SSM) [1, 2] and Metal-organic frameworks (MOF) [5]. The effect the nitrogen chemistry and the type of iron have on the oxygen binding was investigated by ambient pressure X-ray Photoelectron Spectroscopy (XPS) and X-ray Adsorption Spectroscopy (XAS) under an O2 environment at operating temperature of the fuel cell. The effect of the relative abundance of different types of nitrogens, such as pyridinic, coordinated to iron and hydrogenated nitrogens (pyrrolic and hydrogenated pyridine) on the preference of oxygen binding is studied by high-resolution nitrogen photoelectron spectra. The role of metallic and atomically dispersed iron is investigated by a combination of XAS and XPS. Pyridinic N and N-coordinated to metal have been reported as active sites promoting the reduction of oxygen to water while hydrogenated N was hypothesized to reduce oxygen only partially, forming hydrogen peroxide. Figure 1a and 1c shows a difference between N 1s spectra acquired at 200 mTorr total pressure of oxygen/water mixture and that at UHV conditions for two different types of Fe-N-C electrocatalysts. For the catalyst Fe-N-C SSM, the largest change happens in the area of hydrogenated nitrogen while for the catalysts Fe-N-C MOF the largest change is occurring in the region of pyridinic nitrogen. This is also confirmed by different degree of change observed in Fe L-edge upon oxygen binding shown in Figure 1 b and 1d). Rearrangement of Fe(II) and Fe(III) intensity upon oxygen binding is observed only one of the catalysts. Linking differences in oxygen binding to the differences in the chemistry of the electrocatalysts are of ultimate importance for elucidating the oxygen reduction reaction mechanism. 1. Workman, M.J., et al., Platinum group metal-free electrocatalysts: Effects of synthesis on structure and performance in proton-exchange membrane fuel cell cathodes. Journal of Power Sources, 2017. 348: p. 30-39. 2. Gokhale, R., et al., Direct synthesis of platinum group metal-free Fe-N-C catalyst for oxygen reduction reaction in alkaline media. Electrochemistry Communications, 2016. 72: p. 140-143. 3. Strickland, K., et al., Highly active oxygen reduction non-platinum group metal electrocatalyst without direct metal–nitrogen coordination. Nature Communications, 2015. 6: p. 7343. 4. Artyushkova, K., et al., Oxygen Binding to Active Sites of Fe–N–C ORR Electrocatalysts Observed by Ambient-Pressure XPS. The Journal of Physical Chemistry C, 2017. 121(5): p. 2836-2843. 5. Li, J., et al., Structural and mechanistic basis for the high activity of Fe-N-C catalysts toward oxygen reduction. Energy & Environmental Science, 2016. 9(7): p. 2418-2432. Figure 1

Lanthanum-Based Compounds: Electronic Band-Gap-Dependent Electrocatalytic Materials for Oxygen Reduction Reaction.

The electronic energy level of lanthanum compounds plays an important role in the oxygen reduction reaction (ORR) electrocatalytic process. In this work, three lanthanum compounds, LaOHCO3 , La2 O2 CO3 , and La2 O3 , have been synthesized through an in situ urea hydrolysis method, followed by annealing at different temperatures. Among these lanthanum compounds, the layer-structured La2 O2 CO3 has the smallest band gap and moderate values of the conduction band (CB) and valence band (VB). Electrochemical measurements in 0.1 m KOH solution have shown that, compared with the other catalysts, La2 O2 CO3 exhibits the best electrocatalytic activity with the lowest H2 O2 production and highest durability for ORR, which proves the close correlation between electronic energy level and electrocatalytic ORR activity. During the ORR process over La2 O2 CO3 , some covalent electrons from the VB are first excited to the CB and then transfer to the unoccupied π*2p orbitals of an active oxygen molecule, leading to strengthened oxygen adsorption and promotion of the reduction of oxygen. Moreover, La2 O2 CO3 has an ability to chemically disproportionate hydrogen peroxide (to give HO2- ), and the produced HO2- at the energy level of O2 /HO2- can undergo prompt chemical disproportionation into O2 and OH- . The O2 generated at this stage is adsorbed on the catalyst surface, which can be utilized for further oxygen reduction.

RGO/ZnWO4/Fe3O4 nanocomposite as an efficient electrocatalyst for oxygen reduction reaction

Development of low cost, environmental friendly and noble metal free catalyst materials with excellent performance is essential for commercialization. In fact, this is the need of the day too. Herein, we report a facile microwave irradiation method for the synthesis of novel RGO/ZnWO4/Fe3O4 cathode catalysts for the oxygen reduction reaction (ORR) in alkaline medium. The structural and morphological features of synthesized materials are fully examined using transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM). The chemical composition and elemental analysis of the catalyst is investigated by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy techniques. Efficiency of RGO/ZnWO4/Fe3O4 catalyst material for oxygen reduction reaction (ORR) in 0.1M KOH is reported. The activity of catalyst is determined by linear sweep voltammogram (LSV) and rotating disk electrode (RDE) measurements in O2 saturated 0.1M KOH electrolyte. RGO/ZnWO4/Fe3O4 catalyst exhibits higher ORR activity than RGO, ZnWO4, RGO/ZnWO4 and its electrocatalytic performance is comparable to Pt/C material and is superior to it in stability and methanol tolerance. Further, it is determined that process follows a direct four electron reaction pathway. These combined results strongly signpost that RGO/ZnWO4/Fe3O4 composite can function as an economic noble metal free ORR cathode catalyst for energy applications.

Electrospun core–shell nanofibers derived Fe–S/N doped carbon material for oxygen reduction reaction

One-dimensional (1D) nanomaterials have gained attention in energy conversion, storage, and catalyst due to the unique physical and chemical properties. Electrospinning is a kind of simple, versatile, and cost-effective technology to fabricate 1D functional nanofibers. Herein, electrospun polyacrylonitrile (PAN), melamine, and ferric chloride hexahydrate (FeCl3·6H2O) composite nanofibers are used as template, and polythiophene (PT) are prepared by photopolymerization technology on the surface of electrospun nanofibers as shell part of fibers. Then, the core–shell nanofibers are pyrolyzed and converted into Fe–S/N–C nanofibers, which can be used as catalysts for ORR due to the metal and S-/N-codoped structure and unique 1D structure which provided facile pathways for efficient mass transport and charge transfer. The ORR electrocatalytic ability of Fe–S/N–C nanofibers is tested and present excellent property, especially in stability and methanol crossover. The electrocatalytic ability of sample is comparable to that of 20wt% Pt/C benchmarks. These results offer an easy pathway for exploring metal-heteroatom-codoped carbon nanofibers applicable for ORR catalyst.

(Invited) Shape Fixing By Salt Nanoreactor to Produce Nanocarbon Materials for the Catalysis of Oxygen Reduction Reaction

Developing catalytic materials for oxygen reduction reactions (ORR) with high performance and low cost has been one of the major challenges for large-scale applications of fuel cells. We demonstrated a high-yield " shape fixing via salt recrystallization" method to efficiently synthesize N-doped carbon nanomaterials with a high density of active sites, as an ORR catalyst. The process of shape-fixing involves pouring a supersaturated sodium chloride (NaCl) solution onto a 3D polyaniline (PANI) carbon-based polymer in a beaker, which results in the water evaporating and NaCl recrystallizing around the PANI until the PANI is fully covered by crystals. The NaCl crystal functions as a fully sealed nanoreactor which facilitates the N incorporation and graphitization. The gas from gasification in such a closed nanoreactor produces a large quantity of pores in resultant samples, and the carbonized PANI retains its original 3D shape due to previously being shape-fixed by the NaCl crystal. This makes it possible for the active sites (activated by planar pyridinic and pyrrolic N atoms with sp2 hybrid orbitals, which only appear at the outside fringe of a graphene sheet) to appear in large quantities on the edges of numerous pores. Such favorable catalyst structure leads to the availability of efficient mass transport pathways and a high utilization of the active sites in fuel cell. It results in an excellent ORR activity with a half-wave potential only 58 mV behind that of Pt/C in an acidic medium. The proton-exchange membrane fuel cells with the CPANI-Fe-NaCl-catalyzed cathode outputs a peak power of 600 mW cm-2, which is among the best for non-precious metal catalysts reported so far for the ORR. Additionally, no other method is comparable to this invention, in terms of its high yield per batch of N-doped carbon catalysts. The “shape fixing via salt recrystallization” method represents a powerful approach for the preparation of high-performance carbon nanostructures by confined pyrolysis of nanopolymers and, more importantly, provides insight into the design of advanced PEMFC cathode catalysts.

Metal–Organic-Framework-Derived Fe-N/C Electrocatalyst with Five-Coordinated Fe-Nx Sites for Advanced Oxygen Reduction in Acid Media

Even though Fe-N/C electrocatalysts with abundant Fe-Nx active sites have been developed as one of the most promising alternatives to precious metal materials for oxygen reduction reaction (ORR), further improvement of their performance requires precise control over Fe-Nx sites at the molecular level and deep understanding of the catalytic mechanism associated with each particular structure. Herein, we report a host–guest chemistry strategy to construct Fe-mIm nanocluster (NC) (guest)@zeolite imidazole framework-8 (ZIF-8) (host) precursors that can be transformed into Fe-N/C electrocatalysts with controllable structures. The ZIF-8 host network exhibits a significant host–guest relationship dependent confinement effect for the Fe-mIm NCs during the pyrolysis process, resulting in different types of Fe-Nx sites with two- to five-coordinated configurations on the porous carbon matrix confirmed by X-ray absorption near edge structure (XANES) and Fourier transform (FT) extended X-ray absorption fine structure ...

A versatile biomass derived carbon material for oxygen reduction reaction, supercapacitors and oil/water separation

Directly pyrolyzing biowastes has attracted intensive interest, probably because this economical and facile method provides an efficient and versatile platform for synthesizing functional carbons. This study describes the synthesis of different functional carbons from poplar catkins via different processes for multi-purpose applications. Nitrogen and oxygen dual-doped carbon (NODC-800) derived from catkins delivers superior electrochemical characteristics as oxygen reduction reaction (ORR) catalyst in alkaline fuel cell to that of commercial Pt/C in terms of catalytic activity, stability, resistance to methanol cross-over and CO poisoning. In addition, NODC-800 exhibits a high capacity (~251Fg−1 at 0.5Ag−1) with nearly 100% retention rate after 1000 cycles as supercapacitors electrodes. An oleophylic carbon aerogel derived from catkins is proven to be superoleophilic and porous enough to “wet” with oils and organic liquids and repel water completely to achieve oil/water separation. This work is a successful case to take full advantage of raw materials from nature via multiple technologies to achieve energy sustainable development and protect environmental from oils and organic solvents spill.

Nitrogen-Doped Porous Carbon Nanofiber Supported Platinum as Promising Oxygen Reduction Reaction Electrocatalysts

Heteroatoms doped Carbon materials have been proved as promising catalyst support material for oxygen reduction reaction (ORR) in proton exchange membrane fuel cell (PEMFC). In this paper, nitrogen-doped porous nanofibers (N-PCNF) were fabricated via cost effective electrospinning technique by blending the PI and PAN as precursors, followed by heat treatment procedures. The N-PCNFs were used as support to prepare platinum (Pt) catalyst (Pt/N-PCNFs). SEM figure indicated that the porous structures not only existed on the surface but also in the cross session of the fibers. XPS and TEM displayed that with the help of heteroatoms nitrogen, the fiber had rougher surface and more defective structure, contributing to the dispersion of Pt nanoparticles. The catalytic performance for ORR was evaluated by cyclic voltammetry (CV) and liner sweep voltammetry (LSV) with a rotating disk electrode (RDE). According to the results, Pt/N-PCNF exhibited superior property (more positive onset potential and half-wave potential) than that of JM20. The excellent ORR activity of Pt/N-PCNF was attributed to the enriched nitrogen heteroatoms coordinated within the microstructure which increased the exposure of more active sites and dispersion of Pt nanoparticles.

Iodinated carbon materials for oxygen reduction reaction in proton exchange membrane fuel cell. Scalable synthesis and electrochemical performances

Doped graphene-based cathode catalysts are considered as promising competitors for ORR, but their power density has been low compared to Pt-based cathodes, mainly due to poor mass-transport properties. A new electrocatalyst for PEMFCs, an iodine doped grahene was prepared, characterized, and tested and the results are presented in this paper. We report a hybrid derived electrocatalyst with increased electrochemical active area and enhanced mass-transport properties. The electrochemical performances of several configurations were tested and compared with a typical Pt/C cathode configuration. As a standalone catalyst, the iodine doped graphene gives a performance with 60% lower than if it is placed between gas diffusion layer and catalyst layer. If it is included as microporous layer, the electrochemical performances of the fuel cell are with 15% bigger in terms of power density than the typical fuel cell with the same Pt/C loading, proving the beneficial effect of the iodine doped graphene for the fuel cell in the ohmic and mass transfer region. Moreover, the hybrid cathode manufactured by commercial Pt/C together with the material with best proprieties, is tested in a H2-Air fuel cell and a power density of 0.55Wcm−2 at 0.52V was obtained, which is superior to that of a commercial Pt-based cathode tested under identical conditions (0.46Wcm−2).