Doped Carbon Electrocatalysts Research Articles

ZIF-67 derived N doped carbon embedded CoxP for superior hydrogen evolution

Abstract Developing a sustainable non-noble hybrid electrocatalyst for effective electrocatalysis is the most crucial task; particularly in sustainable hydrogen energy production in the realm of energy conversion. In this work, effective thermal pyrolysis process followed by phosphorization strategy was employed to prepare and fabricate ZIF-67 (Zeolitic imidazole) assisted Co2P/N doped carbon electrocatalyst for hydrogen evolution reaction (HER). The optimized Co2P/N–C electrocatalyst exhibited hollow porous nanostructures as confirmed from the scanning electron microscopy. The achieved porous nanostructure improved the efficiency of the charge and mass transportation which is confirmed by the BET analysis, has high surface area value of 94.731 m2/g. In addition, a transition metal atom can regulate reactants adsorption and desorption capacity by modulating Co and P electronic configuration. The electrochemical studies of fabricated ZIF-67 derived Co2P/N–C electrode were analyzed using 1.0 M alkaline potassium hydroxide (KOH) medium in 3 electrode system process. Whilst, optimizing the pyrolysis temperature during the phosphorization will remarkably enhance the favourable characteristics of the hydrogen generation. Notably, the optimized ZIF-67 derived Co2P/NC at 350 °C electrode exhibited low overpotential (135 mV) at minimum 10 mA/cm2 and low 120.3 mV/dec Tafel slope. Besides, electrode stability at 10 mA/cm2 current density was verified by chronoamperometry test. Hence, this study furnishes the potential technique for the development of advanced hybrid MOF electrocatalyst as a successful alternative on large scale.

Mesoporous Single Atom-Cluster Fe-N/C Oxygen Evolution Electrocatalysts Synthesized with Bottlebrush Block Copolymer-Templated Rapid Thermal Annealing.

Current electrocatalysts for oxygen evolution reaction (OER) are either expensive (such as IrO2, RuO2) or/and exhibit high overpotential as well as sluggish kinetics. This article reports mesoporous earth-abundant iron (Fe)-nitrogen (N) doped carbon electrocatalysts with iron clusters and closely surrounding Fe-N4 active sites. Unique to this work is that the mechanically stable mesoporous carbon-matrix structure (79 nm in pore size) with well-dispersed nitrogen-coordinated Fe single atom-cluster is synthesized via rapid thermal annealing (RTA) within only minutes using a self-assembled bottlebrush block copolymer (BBCP) melamine-formaldehyde resin composite template. The resulting porous structure and domain size can be tuned with the degree of polymerization of the BBCP backbone, which increases the electrochemically active surface area and improves electron transfer and mass transport for an effective OER process. The optimized electrocatalyst shows a required potential of 1.48 V (versus RHE) to obtain the current density of 10 mA/cm2 in 1 M KOH aqueous electrolyte and a small Tafel slope of 55 mV/decade at a given overpotential of 250 mV, which is significantly lower than recently reported earth-abundant electrocatalysts. Importantly, the Fe single-atom nitrogen coordination environment facilitates the surface reconstruction into a highly active oxyhydroxide under OER conditions, as revealed by X-ray photoelectron spectroscopy and in situ Raman spectroscopy, while the atomic clusters boost the single atoms reactive sites to prevent demetalation during the OER process. Density functional theory (DFT) calculations support that the iron nitrogen environment and reconstructed oxyhydroxides are electrocatalytically active sites as the kinetics barrier is largely reduced. This work has opened a new avenue for simple, rapid synthesis of inexpensive, earth-abundant, tailorable, mechanically stable, mesoporous carbon-coordinated single-atom electrocatalysts that can be used for renewable energy production.

Graphitic carbon wrapped Co on Zn, Co, N-codoped 3D tremella-like carbon with abundant nanocages for high-performance oxygen reduction

To develop green and renewable energy, subtle design and synthesis of non-precious metal catalysts with low-price, high-efficiency, and robust stability are of paramount significance for oxygen reduction reaction (ORR). In this study, we synthesized graphitic carbon wrapped Co on Zn, Co, N-codoped 3D tremella-like carbon with abundant nanocages (G-Co/Zn, Co, N-TCs) by one-step coordination pyrolysis in the presence of azacytosine. The pyrolysis temperature and Zn/Co feeding ratio were carefully investigated. Integrating the unique structure and synergistic effect of the bimetals, the resulting G-Co/Zn, Co, N-TCs exhibited remarkable ORR activity (Eonset = 0.99 V; E1/2 = 0.88 V vs. RHE), and excellent stability (only 13 mV negative shift of E1/2 after scanning 2000 cycles), outperforming the control groups and commercial Pt/C under alkaline condition. This research presents some precious viewpoints for fabricating advanced N- and transition metal-dual doped carbon electrocatalysts in energy conversion and storage correlated devices.

Insights on Oxygen Reduction Reaction to H2O2: The role of functional groups and textural properties on the activity and selectivity of doped carbon electrocatalysts

Hydrogen peroxide (H2O2) is a key molecule in chemical industrial processes and alterative processes and catalysts are needed to achieve a green in-situ generation. The electrochemical two-electron oxygen reduction (2e-ORR) reactions are one of the most attractive routes along with the water oxidation or the direct synthesis. Here, we focused on the 2e-ORR, summarizing the recent advances in the finalization of catalysts for specifically catalyse the generation of H2O2 and technical measures to improve material screening, especially to obtain reliable activity and selectivity data. Firstly, a brief overview of metal-free catalysts is given and secondly a focus on how different strategies are adopted to improve activity and selectivity is reported. Such strategies include to tune the thermodynamic energy barriers by changing the material composition/functionalization and/or to facilitate mass transfer for reactants and products by acting on morphology. Finally, a brief overview of challenges in ink and electrode preparation for the correct screening of H2O2 electrocatalysts is reported.

Sulfur doped biocarbon obtained from Sargassum spp. for the oxygen reduction reaction

Sulfured doped carbon electrocatalysts is synthesized from the waste biomass Sargassum spp. Two doping procedures are examined to determine which is better for Oxygen Reduction Reaction (ORR); one by doping biocarbon obtained from the pyrolysis of the biomass and the second through a process of in situ doping in autoclave. The electrocatalyst are obtained from pyrolysis of the sample at 700 °C, which is finally characterized as a metal free electrocatalyst for the ORR. The electrocatalyst are characterized by BET surface area analysis, Raman spectroscopy, X-ray Photoelectron Spectroscopy (XPS) and the electrochemical characterization is determined in 0.1 M KOH. The sample SSKPT-1 exhibits a promising electrocatalytic activity with an onset potential of 0.896 V vs RHE and a current density of 5 mA cm−2 (at 0.2 V vs. RHE) which could be partly attributed to its high BET surface area of 2755 m2 g−1.

Edge-enriched N, S co-doped hierarchical porous carbon for oxygen reduction reaction

The development of carbon materials with high electrochemical performance for next-generation energy device is emerging, especially N, S co-doped carbon materials have sparked intensive attention. However, the exploration of N, S co-doped carbon with well-defined active sites and hierarchical porous structures are still limited. In this study, we prepared a series of edge-enriched N, S co-doped carbon materials through pyrolysis of thiourea (TU) encapsulated in zeolitic imidazolate frameworks (TU@ZIF) composites, which delivered very good oxygen reduction reaction (ORR) performance in alkaline medium with onset potential of 0.94 V vs. reversible hydrogen electrode (RHE), good stability and methanol tolerance. Density functional theory (DFT) calculations suggested that carbon atoms adjacent to N and S are probable active sites for ORR intermediates in edge-enriched N, S co-doped carbon materials because higher electron density can enhance O2 adsorption, lower formation barriers of intermediates, improving the ORR performance comparing to intact N, S co-doped carbon materials. This study might provide a new pathway for improving ORR activity by the integration engineering of edge sites, and electronic structure of heteroatom doped carbon electrocatalysts.

Iron and boron-doped carbonized zeolitic imidazolate frameworks as efficient oxygen reduction electrocatalysts for Al-Air batteries

Porous boron-bearing Fe-nitrogen doped carbon electrocatalysts (Fe-BNC) are prepared by pyrolysis treatment of Fe/B co-doped zeolitic imidazolate frameworks (ZIFs). The as-obtained Fe-BNC catalysts with a high surface area (1300 m2 g−1) favor a 4-electron reduction pathway for efficient oxygen reduction reaction (ORR). The Fe-BNC catalysts demonstrate a half-wave potential of ∼0.85 V vs RHE comparable to that of Pt/C catalyst and high stability in 0.1 M KOH. The dopant of little boron and iron into nitrogen-doped carbon results in the high surface area, enhanced surface polarities, electronic properties and exposing more active sites to introduce a synergistic effect for enhanced ORR performance. Moreover, Fe-BNC electrocatalysts used as air cathode for Al-air batteries exhibit a high peak power density of 195.2 mw cm−2 and excellent stability even after discharging for 24 h at room temperature, revealing an excellent performance in application of metal-air batteries and other energy converting devices.

Boosting electrochemical CO2 reduction on ternary heteroatoms-doped porous carbon

Electroreduction of CO2 to value-added chemicals using metal-free carbon catalysts is attractive, but single N-doped carbons suffer from poor efficiency (<90%) and low current density (<2 mA cm−2). Herein, we report a facile and scalable preparation of ternary heteroatoms (N, S, P)-doped carbon electrocatalyst to enhance electrochemical activity, because the multi-heteroatoms with different sizes and electronegativities can modulate the electronic properties to facilitate CO2 localization and provide abundant active sites with enhanced charge-carrier concentrations. It exhibits high activity toward CO2 electroreduction to CO activity with 92% CO Faradaic efficiency (FECO) at −0.7 VRHE and low onset overpotential of 270 mV. The promising potential of industrial application is manifested by the high current density of 245 mA cm−2 and stable FECO above 98% in a flow-cell configuration. Moreover, in-situ Raman spectroscopy demonstrates that *COOH is the key intermediate in CO2-to-CO conversion. Density functional theory calculations reveal that the synergistic effect of N, S, and P heteroatoms boosts the catalytic activity by greatly decreasing the free energy barrier of *COOH formation. Furthermore, the morphological benefit of hierarchically porous structures plays a synergistic role in improving the CO2 reduction activity.

Oxygen Reduction Reaction on Metal and Nitrogen–Doped Carbon Electrocatalysts in the Presence of Sodium Borohydride

Metal and nitrogen–doped carbon electrocatalysts (M–N–C, where M is Fe or Co) were investigated for the oxygen reduction reaction (ORR) in alkaline conditions in the presence of borohydride ions (BH4−). The electrochemical properties of the Fe–N–C and Co–N–C catalysts were investigated by cyclic voltammetry and rotating disk electrode techniques: their ORR electrocatalytic activity was bridged to their physicochemical properties, mainly type of metallic center (Fe vs. Co), structure (atomic dispersion vs. nanoparticles), and BET surface area. It is found that Fe–N–C catalysts have the best performances for the ORR electrocatalysis, even in the presence of BH4− anions. The atomically dispersed Fe- and Co-containing electrocatalysts reach better BH4−-tolerance than their counterparts baring nanoparticles. For the atomically dispersed Fe–N–C electrocatalysts, the lowest BET surface area material generates a slight advantage of ORR mass activity and a poor (and desired) activity for borohydride oxidation reaction (BOR).

Dual-Template Pore Engineering of Whey Powder-Derived Carbon as an Efficient Oxygen Reduction Reaction Electrocatalyst for Primary Zinc-Air Battery.

Cost-effective and high-performance electrocatalysts for oxygen reduction reactions (ORR) are needed for many energy storage and conversion devices. Here, we demonstrate that whey powder, a major by-product in the dairy industry, can be used as a sustainable precursor to produce heteroatom doped carbon electrocatalysts for ORR. Rich N and S compounds in whey powders can generate abundant catalytic active sites. However, these sites are not easily accessible by reactants of ORR. A dual-template method was used to create a hierarchically and interconnected porous structure with micropores created by ZnCl2 and large mesopores generated by fumed SiO2 particles. At the optimum mass ratio of whey power: ZnCl2 : SiO2 at 1 : 3 : 0.8, the resulting carbon material has a large specific surface area close to 2000 m2 g-1 , containing 4.6 at.% of N with 39.7% as pyridinic N. This carbon material shows superior electrocatalytic activity for ORR, with an electron transfer number of 3.88 and a large kinetic limiting current density of 45.40 mA cm-2 . They were employed as ORR catalysts to assemble primary zinc-air batteries, which deliver a power density of 84.1 mW cm-2 and a specific capacity of 779.5 mAh g-1 , outperforming batteries constructed using a commercial Pt/C catalyst. Our findings open new opportunities to use an abundant biomaterial, whey powder, to create high-value-added carbon electrocatalysts for emerging energy applications.

Highly Active and Durable Transition Metal-Coordinated Nitrogen Doped Carbon Electrocatalyst for Oxygen Reduction Reaction in Neutral Media

The major technical obstacles in commercialization of microbial fuel cell technology are the sluggish kinetic, high cost, and poor durability of an air cathode electrocatalyst. This research aimed to synthesize the highly active, stable and low cost non-precious metal catalyst to replace the expensive Pt electrocatalyst using a simple, low cost and scalable method. The Fe3C and Fe-N-C catalysts were prepared by direct heating the precursors under autogenic pressure conditions. X-ray diffraction pattern revealed the phase of Fe3C sample was cohenite Fe3C and graphitic carbon, while the phase of Fe-N-C catalyst was only graphitic carbon. The morphology of the synthesized catalysts was a highly porous structure with nanoparticle morphology. The surface area of the Fe3C and the Fe-N-C catalysts was 295 and 377 m2 g-1, respectively. The oxygen reduction reaction (ORR) activity of Fe-N-C catalyst was more active than Fe3C catalyst. The ORR performance of Fe-N-C catalyst exhibited about 1.6 times more superior to that of the noble Pt/C catalyst. In addition, the Fe-N-C catalyst was durable to operate under neutral media. Thus, a novel autogenic pressure technique was a promising method to effectively prepare an highly active and durable non-precious metal catalyst to replace the precious Pt/C catalyst.

Nitrogen doped carbon fibers derived from carbonization of electrospun polyacrylonitrile as efficient metal-free HER electrocatalyst

Development of durable and efficient electrocatalyst for hydrogen evolution reaction (HER) is significantly important for forwarding the commercialization of water splitting technology. In this work, we report a facile synthesis of nitrogen doped carbon fibers derived from the carbonization of the electron-spun polyacrylonitrile (PAN) membrane at 800 °C (NCFs-800) as efficient and stable metal-free electrocatalyst for HER catalysis in both acidic and alkaline mediums. Ascribing to the homogenous nitrogen dopants in electrocatalyst, NCFs-800 requires only 114.3 mV and 198.6 mV vs. RHE to achieve current density of 10 mA cm−2 in 0.5 M H2SO4 and 1 M KOH electrolytes, respectively. Moreover, the HER activity is well maintained after 2000 potential cycles indicating that NCFs-800 possesses high durability in both acidic and alkaline conditions due to the fibrous structure with high corrosion resistance. Our study offers new strategy to synthesize stable and efficient metal-free electrocatalyst, which could be extended to other heteroatom doped carbon electrocatalyst.

Phosphorus and Iron Doped-Porous Carbon As an Efficient Electrocatalyst for Oxygen Reduction Reaction in Alkaline Medium

The U.S. Energy Information Administration has projected a 27% growth in energy consumption by the year 2050.1 The continuous increase in the energy demands worldwide and the environmental concerns reaching critical levels, has required researchers to make the development of clean and sustainable energy conversion devices their paramount challenge. Fuel cells and metal-air batteries with high efficiency and low cost are the prime candidates. Platinum loaded carbon substrate is the catalyst of choice in fuel cells for anodic oxidation of H2 and cathodic reduction of O2 but large-scale commercial production is restricted by its prohibitive cost, limited supply, and weak durability.2 Platinum’s vulnerability to potential drift over time and easy loss of activity through methanol poisoning, questions its competitive catalytic activity. Electrocatalyst that are easily synthesized, have low cost and are earth-abundant is still highly desired. Heteroatom doped carbon electrocatalysts are highly considered candidates and are well researched because of their high abundance and low cost, with transition metal and nitrogen doped carbon material showing competitive result towards the oxygen reduction reaction (ORR).3 , 4 Among those heteroatoms phosphorus doped carbon is an emerging catalyst with high potential. The attraction towards phosphorus arises from the fact that it has a larger atomic radius- hence larger covalent radius- and higher electron-donating ability than nitrogen, making it a promising dopant with an ability to modify the electron transport properties. The Introduction of phosphorus, an atom with lower electronegativity, changes the charge density distribution and electronic properties of a high surface area carbon structure. Phosphorus doping increases the affinity towards an acceptor molecule such as oxygen5, hence a better interaction with the oxygen intermediate and enhances their electrocatalytic activities towards ORR. Such heteroatoms are typically covalently bonded within a carbon framework ensuring long-term stability. The advantages of a heteroatom doped porous carbon are twofold, stabilization of the non-precious metal in the alkaline medium and generation of active sites for facilitating the oxygen reduction reaction. Electrocatalytic activity of phosphorus doped and iron treated phosphorus doped carbon has only been covered by few groups and needs more improvements.6,7 The purpose of the study of electron transfer processes is to understand the reactivity of a relatively new, doped porous carbon complexes incorporating phosphorus as a heteroatom bonded to a metal center. According to DFT calculations, O2 and other ORR intermediates can be stably adsorbed on to Fe sites8, making phosphorus and iron doped carbon a prime candidate for ORR. Using a single precursor as a source of phosphorus, we propose a simple one-step chemical activation, with anhydrous ZnCl2 and anhydrous FeCl2 as the agents of carbonization, yielding P and Fe-doped porous carbon (PFeC). The electrocatalytic activity towards ORR was studied using a rotating ring-disk electrode (RRDE) technique and rotating disk electrode (RDE) connected to the CHI 600 potentiostat. The electrochemical activity of PFeC was compared with the commercially available 20 wt% Pt/C. PFeC showed high activity towards ORR, with comparable onset potential and a small negative shift in half-wave potential. PFeC electrocatalyst selectively catalyzes oxygen to water via a direct four-electron pathway. PFeC showed to be inert toward alcohol oxidation and had superior long-term stability. References (1) U.S. EIA. Annual Energy Outlook 2018 with Projections to 2050. Annu. Energy Outlook 2018 with Proj. to 2050 2018, 44 (8), 1–64. (2) Steele, B. C.; Heinzel, A. Materials for Fuel-Cell Technologies. Nature 2001, 414 (November), 345–352. (3) Lin, L.; Zhu, Q.; Xu, A. W. Noble-Metal-Free Fe-N/C Catalyst for Highly Efficient Oxygen Reduction Reaction under Both Alkaline and Acidic Conditions. J. Am. Chem. Soc. 2014, 136 (31), 11027–11033. (4) Gong, K.; Du, F.; Xia, Z.; Durstock, M.; Dai, L. Nitrogen-Doped Carbon Nanotube Arrays with High Electroctalytic Activity for Oxygen Reduction. Science (80-. ). 2009, 323 (FEBRUARY), 760–764. (5) Cruz-Silva, E.; Lopez-Urias, F.; Munoz-Sandoval, E.; Sumpter, B. G.; Terrones, H.; Charlier, J. C.; Meunier, V.; Terrones, M. Phosphorus and Phosphorus-Nitrogen Doped Carbon Nanotubes for Ultrasensitive and Selective Molecular Detection. Nanoscale 2011, 3 (3), 1008–1013. (6) Razmjooei, F.; Singh, K. P.; Bae, E. J.; Yu, J.-S. A New Class of Electroactive Fe- and P-Functionalized Graphene for Oxygen Reduction. J. Mater. Chem. A 2015, 3 (20), 11031–11039. (7) Singh, K. P.; Bae, E. J.; Yu, J. S. Fe-P: A New Class of Electroactive Catalyst for Oxygen Reduction Reaction. J. Am. Chem. Soc. 2015, 137 (9), 3165–3168. (8) Lee, D. H.; Lee, W. J.; Lee, W. J.; Kim, S. O.; Kim, Y. H. Theory, Synthesis, and Oxygen Reduction Catalysis of Fe-Porphyrin-like Carbon Nanotube. Phys. Rev. Lett. 2011, 106 (17), 8–11.

Enhancing Li-S redox kinetics by fabrication of a three dimensional Co/CoP@nitrogen-doped carbon electrocatalyst

The design of sulfur hosts with high electrochemical activity and high sulfur loading plays a vital role in developing high-energy-density lithium-sulfur batteries. Herein, a novel type of sulfur cathode substrate is established via a facile two-step process, in which the Co and CoP nanoparticles are embedded in a three-dimensional (3D) porous nitrogen-doped carbon polyhedron (Co/CoP@NC). These Co and CoP nanograins not only act as polysulfides capturing centers but also the electrocatalysts effectively promoting the redox kinetics towards polysulfides conversion, as confirmed by the experimental results and DFT calculations. Meanwhile, the interconnected 3D porous N-doped carbon architecture contributed to Li+ transportation, electrolyte infiltration and relieves volume expansion of sulfur. Thus, Li-S batteries configured with the S@Co/CoP@NC cathode exhibit a remarkable enhancement in the rate capability and cycling performances. When sulfur content is controlled to be 75.8 wt%, the S@Co/CoP@NC cathode delivers an outstanding high-rate capability up to 30 C and low capacity decay rates of 0.033% and 0.03% per cycle over 1000 cycles at 1 C and 2 C, respectively.

Cyanogenic glycosides: A sustainable carbon and nitrogen source for developing resilient Janus reversible oxygen electrocatalysts for metal-air batteries

Most of the transition metal based heteroatom doped carbon electrocatalysts, utilizes the fossil fuel derived commercially available precursors as source of nitrogen and carbon which may question our environmental generosity. Herein, we have developed Ni-based efficient bifunctional electrocatalysts using apple seeds (that contains cyanogenic glycosides) as the precursor for nitrogen and carbon. With tuning the temperature, we were able to optimize the nitrogen doping up to ∼3 at.%. The optimized electrocatalyst catalyses the oxygen reduction reaction (ORR) process with muted peroxide generation (for 0.750–0.1 V the % HO2− generation ∼3 - 2%), preferential 4e− reduction pathways (n ∼ 3.93 to 3.98 in 0.75–0.1 V range) and electron transfer via inner-sphere electron transfer mechanism which ensures the maximum utilization of instituted active centres owing to the direct interaction of reactant species. Alike to ORR, the superior oxygen evolution reaction (OER) performance with smaller Eonset, EJ=10, Tafel slope and enduring accelerated stability test advocates its potential as a bifunctional oxygen electrocatalyst. Moreover, smaller potential gap ΔE (EJ10_OER - E1/2_ORR) of 0.845 V further warrants the energy efficient OER/ORR process. A porotype of Al-air battery system using our catalysts as oxygen electrode and chocolate wafer as anode material is well capable of powering the light emitting diodes. This study hopefully opens a new avenue to explore cyanogenic glycosides plants product to develop multifunctional electrocatalysts.

Phosphorus and Iron Doped-Porous Carbon As an Efficient Electrocatalyst for Oxygen Reduction Reaction in Alkaline Medium

The U.S. Energy Information Administration has projected a 27% growth in energy consumption by the year 2050.1 The continuous increase in the energy demands worldwide and the environmental concerns reaching critical levels, has required researchers to make the development of clean and sustainable energy conversion devices their paramount challenge. Fuel cells and metal-air batteries with high efficiency and low cost are the prime candidates. Platinum loaded carbon substrate is the catalyst of choice in fuel cells for anodic oxidation of H2 and cathodic reduction of O2 but large-scale commercial production is restricted by its prohibitive cost, limited supply, and weak durability.2 Platinum’s vulnerability to potential drift over time and easy loss of activity over methanol poisoning, questions its competitive catalytic activity in comparison to Pt or Pt-alloy based catalyst and are easily synthesized, have low cost and are earth-abundant is still highly desired. Heteroatom doped carbon electrocatalysts are highly considered and well researched because of their high abundance and low cost, with transition metal and nitrogen doped carbon material showing competitive result towards the oxygen reduction reaction (ORR).3 , 4 Among those heteroatoms phosphorus doped carbon is an emerging catalyst with high potential. The attraction towards phosphorus arises from the fact that it has a larger atomic radius- hence larger covalent radius- and higher electron-donating ability than nitrogen, making it a promising dopant with an ability to modify the electron transport properties. The Introduction of phosphorus, an atom with lower electronegativity, changes the charge distribution and electronic properties of high surface area carbon structure. Phosphorus doping increases the affinity towards an acceptor molecule such as Oxygen5, hence a better interaction with the oxygen intermediate and enhances their electrocatalytic activities towards ORR. Such heteroatoms are typically covalently bonded within a carbon framework ensuring long-term stability. The advantages of a heteroatom doped porous carbon are twofold, stabilization of the non-precious metal in the alkaline medium and generation of active sites for facilitating the oxygen reduction reaction. Electrocatalytic activity of phosphorus doped and Iron treated phosphorus doped carbon has only been covered by few groups and needs more improvements.6,7 The purpose of the study of electron transfer processes is to understand the reactivity of a relatively new, doped porous carbon complexes incorporating the Phosphorus as a heteroatom bonded to a metal center. According to DFT calculations, O2 and other ORR intermediates can be stably adsorbed on to Fe sites8, making phosphorus and iron doped carbon a prime candidate for ORR. Using a single precursor as a source of phosphorus, we propose a simple one-step chemical activation, with anhydrous ZnCl2 and anhydrous FeCl2 as the agents of carbonization, yielding P and Fe-doped porous carbon (PFeC). The electrocatalytic activity towards ORR was studied using a rotating ring-disk electrode (RRDE) technique and rotating disk electrode connected to the CHI 600 potentiostat. The electrochemical activity of PFeC was compared with the commercially available 20 wt% Pt/C. PFeC showed high activity towards ORR, with comparable onset potential and a small negative shift in half-wave potential. PFeC selectively catalyzes oxygen to water via a direct four-electron pathway. PFeC showed to be inert toward alcohol oxidation and had superior long-term stability. References (1) U.S. EIA. Annual Energy Outlook 2018 with Projections to 2050. Annu. Energy Outlook 2018 with Proj. to 2050 2018, 44 (8), 1–64. (2) Steele, B. C.; Heinzel, A. Materials for Fuel-Cell Technologies. Nature 2001, 414 (November), 345–352. (3) Lin, L.; Zhu, Q.; Xu, A. W. Noble-Metal-Free Fe-N/C Catalyst for Highly Efficient Oxygen Reduction Reaction under Both Alkaline and Acidic Conditions. J. Am. Chem. Soc. 2014, 136 (31), 11027–11033. (4) Gong, K.; Du, F.; Xia, Z.; Durstock, M.; Dai, L. Nitrogen-Doped Carbon Nanotube Arrays with High Electroctalytic Activity for Oxygen Reduction. Science (80-. ). 2009, 323 (FEBRUARY), 760–764. (5) Cruz-Silva, E.; Lopez-Urias, F.; Munoz-Sandoval, E.; Sumpter, B. G.; Terrones, H.; Charlier, J. C.; Meunier, V.; Terrones, M. Phosphorus and Phosphorus-Nitrogen Doped Carbon Nanotubes for Ultrasensitive and Selective Molecular Detection. Nanoscale 2011, 3 (3), 1008–1013. (6) Razmjooei, F.; Singh, K. P.; Bae, E. J.; Yu, J.-S. A New Class of Electroactive Fe- and P-Functionalized Graphene for Oxygen Reduction. J. Mater. Chem. A 2015, 3 (20), 11031–11039. (7) Singh, K. P.; Bae, E. J.; Yu, J. S. Fe-P: A New Class of Electroactive Catalyst for Oxygen Reduction Reaction. J. Am. Chem. Soc. 2015, 137 (9), 3165–3168. (8) Lee, D. H.; Lee, W. J.; Lee, W. J.; Kim, S. O.; Kim, Y. H. Theory, Synthesis, and Oxygen Reduction Catalysis of Fe-Porphyrin-like Carbon Nanotube. Phys. Rev. Lett. 2011, 106 (17), 8–11.

A proposal based on quantum phenomena for the ORR mechanism on nitrogen-doped carbon-based electrocatalysts

Abstract Several theories have tried to explain the role of nitrogen-doped carbon-based electrocatalysts during the oxygen reduction reaction (ORR). However, there is no consensus about which of the existing theories is most accurate. In this work, we propose a hypothesis presented for the first time, which consists on the hybridization change of carbon atoms in the graphene lattice, from sp2 to sp3. As shown in several studies, carbons with sp3 hybridization can store electrons (i.e. work as capacitors), this phenomenon, along with nitrogen inversion, due to lattice defects, would allow the nitrogen atom to works as a “switch”, enabling or stopping the flow of electrons, generating active sites that enhance the ORR. Computational chemistry was used to prove this hypothesis. A graphene of 92 atoms doped and undoped has been constructed using the Gauss View 5.0® program, the geometries were optimized by DFT in Gaussian 0.9® software, in order to compare changes in bond angles and lengths of the lattices, and map the electrostatic potential distribution (ESP). The results obtained in the measurement of the angles and charges around the doping nitrogen presented interesting results that can help to demonstrate part of the established hypothesis about nitrogen inversion. The study shows that it is possible that this phenomenon increases when there are a greater number of defects in the lattice. Understanding this phenomenon will help to develop and know the best synthesis conditions for doped carbon electrocatalysts.

Heteroatom-Doped Carbon Materials for Hydrazine Oxidation.

The key in designing efficient direct liquid fuel cells (DLFCs), which can offer some solutions to society's grand challenges associated with sustainability and energy future, currently lies in the development of cost-effective electrocatalysts. Among the many types of fuel cells, direct hydrazine fuel cells (DHFCs) are of particular interest, especially due to their high theoretical cell voltages and clean emission. However, DHFCs currently use noble-metal-based electrocatalysts, and the scarcity and high cost of noble metals are hindering these fuel cells from finding large-scale practical applications. In order to replace noble-metal-based electrocatalysts with sustainable ones and help DHFCs become widely usable, great efforts are being made to develop stable heteroatom (e.g., B, N, O, P and S)-doped carbon electrocatalysts, the activities of which are comparable to, or better than, those of noble metals. Here, the recent research progress and the advancements made on the development of heteroatom-doped carbon materials, their general properties, their electrocatalytic activities toward the HzOR, and their dopant- and structure-related electrocatalytic properties for the HzOR are summarized. Perspectives on the different directions that the research endeavors in this field need to take in the future and the challenges associated with DHFCs are included.

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).

Facile approach for synthesis of doped carbon electrocatalyst from cellulose nanofibrils toward high-performance metal-free oxygen reduction and hydrogen evolution

Multi-element doped metal-free carbon nanomaterials with a 3D architecture were prepared from inexpensive and naturally abundant cellulose nanofibrils. Compared to the most graphene-based carbons reported in the literature that show only good oxygen reduction reaction (ORR) activity, our N,S-doped carbon nanofiber network coated with N,P-doped carbon nanoparticles showed good bifunctionality toward ORR and hydrogen evolution reaction (HER) activities. The HER performance with doped carbon material exhibited an onset potential of 233mV (vs. RHE), a current density of 10mAcm-2 at 331mV (vs. RHE), and Tafel slope of 99mVdecade−1. The same material was also used for ORR, which could deliver an onset potential 10mV more negative than commercial Pt/C and a cathodic peak of 0.84V (vs. RHE). These values are better than most reported metal-free electrocatalysts. The superior performance of carbon hybrid may be attributed to the combination of a more exposed highly active N,P-doped carbon, a good integration of N,P-doped carbon with N,S-doped carbon nanofibers, and an accelerated electron transport through N,S-doped carbon nanofibers as good conductivity channels.