Heteroatom Co-doping Research Articles

(Invited) Co-Doping Strategy for Enhanced Photoelectrochemical Water Splitting Performan

Titanium and heteroatom-codoped hematite photoanodes showed significantly increased photoelectrochemical (PEC) water splitting activity. The Ti and heteroatom co-doping in hematite not only suppresses the number of metal ions that cause electron hole pair (EHP) recombination at the hematite surface but also generates an internal electric field for easy hole extraction. The co-doped hematite converted the incident photons to EHPs with much reduced recombination and exhibited an excellent photocurrent density of greater than 2.5 mA/cm2 at 1.23 VRHE. Our co-doping strategy provides a straightforward way of addressing the chronic short-hole diffusion length issue that causes a high electron hole recombination rate, to potentially improve the performance of PEC devices.

Nitrogen and sulfur co-doped reduced graphene oxide-gold nanoparticle composites for electrochemical sensing of rutin

The extraordinary biological and physiological properties of rutin have been used in the preparation of therapeutical drugs. So it is very significant to develop a simple and sensitive method for rutin determaination in pharmaceutical samples. Herein, nitrogen and sulfur co-doped reduced graphene oxide attached with gold nanoparticles (NS-rGO/AuNPs) was developed for electrochemical determination of rutin. The NS-rGO was first prepared by a simple one-step thermal annealing method, and AuNPs were embedded onto NS-rGO through the interaction force of Au with N and S atoms. Detailed characterizations showed that the AuNPs are well dispersed and the presence of nitrogen and sulfur are significant. The NS-rGO/AuNPs modified electrode exhibited a significantly enhanced electrocatalytic activity towards rutin compared with NS-rGO, N-rGO and S-rGO modified electrodes. The excellent performance was achieved by the synergistic effect of AuNPs and heteroatoms co-doping. As a consequence, the NS-rGO/AuNPs based sensor showed a wide linear range of 0.2–1400 nM with a nanomolar detection limit of 0.067 nM (S/N = 3). Also the sensor exhibited satisfying selectivity, reproducibility, and stability. Finally, the sensor was successfully used to determine rutin in pharmaceutical tablets.

In situ W/O Co-doped hollow carbon nitride tubular structures with enhanced visible-light-driven photocatalytic performance for hydrogen evolution

Heteroatom co-doping has been considered as an effective strategy to simultaneously overcome intrinsic shortcomings of g-C3N4 to achieve enhanced photocatalytic properties, in which the involved dopants could play its role in altering electronic structure, optical absorption and charge separation of the catalyst. Herein, W/O co-doped hollow g-C3N4 tubular structures are successfully obtained for the first time via a one-step thermal decomposition. By W/O co-doping, architecture of g-C3N4 is able to be modulated with enhanced optical absorption towards visible region. In addition, narrowed band gap and restrained charge recombination are conducive for the excitation of electron-hole pairs and transportation. Photocatalytic water splitting tests indicate that the co-doped hollow tubular g-C3N4 structures enable superior activity for generating hydrogen up to 403.57 μmol g−1 h−1 driven by visible light, nearly 2.5 times as high as that of pristine g-C3N4. This work presents a rational strategy to design co-doped g-C3N4 as an efficient visible-light-driven photocatalyst.

Macro-microporous carbon with a three-dimensional channel skeleton derived from waste sunflower seed shells for sustainable room-temperature sodium sulfur batteries

Macro-microporous carbon (MMC), with a three-dimensional channel skeleton and co-doping of heteroatoms derived from waste sunflower seed shells, was synthesized through a facile chemical-activation process. The three-dimensional channel skeleton with a macroporous structure of the MMC formed an interwoven carbon network that effectively improved the electrical conductivity and facilitated the transfer of Na+ in the cell by allowing the electrolyte to permeate easily. The micropores (<0.7 nm) of the MMC are the main sulfur host and serve to trap the small sulfur molecules (<0.5 nm) within the pores, resulting in excellent electrochemical performance in room-temperature sodium sulfur (RT Na–S) batteries with a carbonate-based electrolyte. The co-doping of heteroatoms (N, O) in the MMC matrix can create an active site that improves the electrical conductivity and builds an interaction with sulfur species to inhibit polysulfide shuttling. The confinement of sulfur through these physical and chemical mechanisms results in a high initial discharge capacity of 1598 mAh g−1 at 0.1 C and a superior capacity retention of 330 mAh g−1 after 510 cycles at 1 C. This study provides an attractive material derived from biomass for low-cost and sustainable RT Na–S batteries.

Up-Scalable Conversion of White-Waste Polystyrene Foams to Sulfur, Phosphorus-Codoped Porous Carbon for High-Performance Lithium–Sulfur Batteries

Discarded polystyrene foams as white wastes, at least two million tons in demand annually in China, are threatening environment and health because of their formidable degradation, which increase in quantity with a reported rate of about 15% per year. Here, we employ a facile and up-scalable approach to convert discarded polystyrene foams to S,P-codoped porous carbon (SPPC) as the effective sulfur mobilizer for lithium–sulfur batteries. The high porosity of SPPC can ensure high loading of sulfur with effective physical adsorption to polysulfides, and the heteroatom codoping of sulfur and phosphorus can enhance the electrical conductivity of carbon effectively with strong chemical immobilization for polysulfides. These effects are together responsible for the superior performance of S@SPPC with a sulfur loading of 72 wt %. The S@SPPC cathode with an areal sulfur loading of 2 mg cm–2 exhibits an initial capacity of 893 mA h g–1 at 2 C with only a small capacity loss of 0.049% per cycle over 800 cycles. The cathode still exhibits both superior rate capability, and stable cycling performance for a capacity decay rate of 0.06% per cycle over 600 cycles at 2 C by increasing the areal sulfur loading to 4.8 mg cm–2 and a capacity of 694 mA h g–1 retained after 150 cycles for 0.5 C at a much reduced electrolyte-to-sulfur ratio of 5 mL g–1. This study offers a route for realizing the up-scalable conversion of “waste” to “treasure,” which is significant for practical applications in energy storage.

Toward Highly Selective Electrochemical CO2 Reduction using Metal-Free Heteroatom-Doped Carbon.

There are growing interests in metal‐free heteroatom‐doped carbons for electrochemical CO2 reduction. Previous studies extensively focus on the effect of N‐doping, and their products severely suffer from low current density (mostly <2 mA cm−2) and limited selectivity (<90%). Here, it is reported that heteroatom codoping offers a promising solution to the above challenge. As a proof of concept, N,P‐codoped mesoporous carbon is prepared by annealing phytic‐acid‐functionalized ZIF‐8 in NH3. In CO2‐saturated 0.5 m NaHCO3, the catalyst enables CO2 reduction to CO with great selectivity close to 100% and large CO partial current density (≈8 mA cm−2), which are, to the best of knowledge, superior to all other relevant competitors. Theoretical simulations show that the improved activity and selectivity are stemmed from the enhanced surface adsorption of *COOH and *CO intermediates as a result of the synergy of N and P codoping.

(Invited) Boron and Nitrogen Co-Doped Porous Carbon Nanofibers As Metal-Free Electrocatalysts for Highly Efficient Ammonia Electrosynthesis

NH3 synthesis via the electrocatalytic nitrogen reduction reaction (NRR) under ambient conditions has been regarded as a sustainable strategy for fertilizer production, hydrogen fuel storage, and mitigating greenhouse gas emissions. Electrochemical reduction reaction of nitrogen to ammonia has been widely investigated as a potential technology to overcome thermodynamic barrier of high-temperature and high-pressure needed for industrial Haber-Bosch process. The design of construction of heteroatoms (e.g., B, N, P, S) doped carbon materials have become a research focus as metal-free electrocatalysts owing to their good electrochemical stability and high electronic conductivity. N-doping carbon materials could induce the protonated pyridinic N and adjacent atomic vacancy site, which are favor of N2 adsorption. Besides, on account of charge density difference, B-doping carbon materials could induce inhomogeneity for carbon to adsorb N2 molecules. Compared with single heteroatom dopant, heteroatom co-doping could bring in charge redistribution of carbon, which can facilitate the chemisorption of N2 molecules and following electron transfer.Herein, we present a metal-free B and N co-doped porous carbon nanofibers (B/N-CNF) fabricated by an electrospinning and calcination strategy. The FESEM image of B/N-CNF showed the typical morphology of the cross-linked carbon networks composed of nanofibers with a diameter of ~100 nm. The contents of B and N dopant for B/N-CNF were 29.9% and 27.6%, respectively. The N2 adsorption-desorption isotherms curve of B/N-CNF exhibited a high BET specific surface area of 748 m2 g-1 and a mesopores structure with pore diameter of around 4 nm and volume of ~0.39 cm3 g-1. Benefitting from a high surface area and synergistic effect between B and N dopants, the B/N-CNF exhibited a high electrocatalytic activity for NRR in a basic electrolyte, achieving the highest FE of 13.2% at -0.5 V and the NH3 yield rate of 32.5 μg h-1 mg-1 cat. at -0.7 V. Such a high NRR activity was superior to most of the previously reported B- or N- doped carbon materials. It was found that B atoms facilitated the cleavage of N≡N bonds, and the N atoms enhanced the electronic conductivity of CNF nanofibers.The B/N-CNF delivered superior catalytic activity for electrochemical NRR, featured by the highest FE of 13.2% at -0.5 V and NH3 yield of 32.5 μg h-1 mg-1 cat. at -0.7 V in basic electrolytes. The high NRR performance could be attributed to the synergistic effect between B and N co-dopants. The FE value of B/N-CNF was almost the highest among all previously reported carbon-based materials with single N- or B-doping. Moreover, an electrolyzer with B/N-CNF as the cathode and commercial Ir/C as the anode was successfully fabricated to confirm the NRR activity of B/N-CNF driven by alkaline batteries and solar panels. The developed B/N-CNF presented in this work paves a promising pathway for rational design of highly efficient dual heteroatoms doped carbon materials for not only NRR, but other electrochemical energy conversion reactions.

Poly(Ionic Liquid)-Derived Graphitic Nanoporous Carbon Membrane Enables Superior Supercapacitive Energy Storage.

High energy/power density, capacitance, and long-life cycles are urgently demanded for energy storage electrodes. Porous carbons as benchmark commercial electrode materials are underscored by their (electro)chemical stability and wide accessibility, yet are often constrained by moderate performances associated with their powdery status. Here via controlled vacuum pyrolysis of a poly(ionic liquid) membrane template, advantageous features including good conductivity (132 S cm-1 at 298 K), interconnected hierarchical pores, large specific surface area (1501 m2 g-1), and heteroatom doping are realized in a single carbon membrane electrode. The structure synergy at multiple length scales enables large areal capacitances both for a basic aqueous electrolyte (3.1 F cm-2) and for a symmetric all-solid-state supercapacitor (1.0 F cm-2), together with superior energy densities (1.72 and 0.14 mW h cm-2, respectively) without employing a current collector. In addition, theoretical calculations verify a synergistic heteroatom co-doping effect beneficial to the supercapacitive performance. This membrane electrode is scalable and compatible for device fabrication, highlighting the great promise of a poly(ionic liquid) for designing graphitic nanoporous carbon membranes in advanced energy storage.

Simultaneous Cobalt and Phosphorous Doping of MoS2 for Improved Catalytic Performance on Polysulfide Conversion in Lithium–Sulfur Batteries

AbstractThe lithium–sulfur batteries are susceptible to the loss of sulfur as dissolved polysulfides in the electrolyte and their ensuing redox shutting effect. The acceleration of the conversion kinetics of dissolved polysulfides into the insoluble sulfur and lithium sulfide via electrocatalysis has the appeal of being a root‐cause solution. MoS2 is the most common electrocatalyst used for this purpose. It is demonstrated that how the effectiveness can be improved by simultaneous cobalt and phosphorus doping of MoS2 nanotubes (P‐Mo0.9Co0.1S2‐2, containing 1.81 at% of P). Cobalt doping induces the transformation of MoS2 from 2H phase to metallic 1T phase, which improves the electrical conductivity of the MoS2. The Co–P coordinated sites on the catalyst surface are highly active for the polysulfide conversion reactions. Consequently, a sulfur cathode with P‐Mo0.9Co0.1S2‐2 can decrease the capacity fade rate from 0.28% per cycle before modification (over 150 cycles at 0.5C rate) to 0.046% per cycle after modification (over 600 cycles at 1C rate). P‐Mo0.9Co0.1S2‐2 also enhances the high rate performance from a capacity of 338 to 931 mAh g−1 at 6C rate. The results of this study provide the first direct evidence of the beneficial effects of heteroatom codoping of polysulfide conversion catalysts.

Biomass derived interconnected hierarchical micro-meso-macro- porous carbon with ultrahigh capacitance for supercapacitors

The cost-effective biomass derived carbon with high electrochemical performance is highly desirable for the sustainable development of advanced energy storage devices. However, most of the reported biomass carbon materials suffer from the low capacitance in the range of 0–400 F/g as the electrode for supercapacitor. Herein, we reported, for the first time, the fabrication of tri-modal porous carbon with a record high capacitance of 550 F/g at 0.2 A/g for biochar materials from shaddock endotheliums by a feasible method combined with metal ion impregnation and molten KOH activation. The as-prepared carbon also showed an outstanding energy density of 46.88 Wh/kg with a power density of 300 W/kg in 1 M BMIMBF4/AN with high capacitance retention over 93.7% after 10000 cycles, which is rarely achieved by the peer reported biochars. Its high electrochemical performance is attributed to combined contributions from high surface area (1265 m2/g), hierarchical porous structure, high graphitization level and abundant heteroatoms (about 10 atom%) co-doping. The work provides an outstanding renewable candidate and a feasible route design strategy for fabrication of high performance electrode materials.

Facile synthesis of mesoporous and highly nitrogen/sulfur dual-doped graphene and its ultrahigh discharge capacity in non-aqueous lithium oxygen batteries

High-level heteroatom, N and S, dual-doped graphene with an improved mesoporous structure was fabricated via facile in situ carbonization and used as metal-free cathode for non-aqueous lithium oxygen batteries. The prepared cathode delivered an ultrahigh specific capacity of 22,252 mAh/g at a current density of 200 mA/g as well as better cycling reversibility because of the larger and copious mesopores, which can promote the penetration of oxygen, electrons, and lithium ions and the ability to accommodate more discharge products, e.g., Li2O2, in Li–O2 batteries. The material had a high level of heteroatom co-doping in the carbon lattice, which enhanced the electrical conductivity and served as active sites for the oxygen reduction reaction.

Heteroatoms co-Doping (N, F) to the Porous Carbon Derived from Spent Coffee Grounds as an Effective Catalyst for Oxygen Reduction Reaction in Polymer Electrolyte Fuel Cells

Toward development of alternative metal-free oxygen reduction reaction catalyst, engineering heteroatoms and tuning defects, pore geometry in porous carbon is explored in this study. Simultaneous co-doping of nitrogen and fluorine heteroatoms to porous carbon matrix derived from spent coffee grounds is synthesized and studied for their structural and electrochemical properties. Microscopic analysis of N-F co-doped coffee carbon (N-F/CC) undergoes morphological evolution in its textural properties includes geometrical surface area, pore structure and defects associated with them, features responsible for creating active sites toward ORR activity. N-F/CC catalyst exhibits excellent ORR catalytic activity, methanol and carbon monoxide tolerance in both acidic and alkaline media which makes it highly potential as metal-free oxygen reduction reaction catalyst for polymer electrolyte fuel cell. The developed catalyst is subjected to 10,000 repeated potential cycles in both media and is stable with no degradation in ORR activity. XPS analysis of N-F/CC catalyst revealed the presence of N in the forms of pyridinic-N, pyrrolic-N, graphitic-N, active species and F in the forms of C-F ionic and C-F semi-ionic active forms. Co-existence of all these active species induces the maximum C-C bond polarization, charge re-distribution and high spin densities in the carbon matrices and synergistically ORR activity.

Synergistic effects of phosphorous/sulfur co-doping and morphological regulation for enhanced photocatalytic performance of graphitic carbon nitride nanosheets

Graphitic carbon nitride (g-C3N4) as a metal-free polymer semiconductor has received extensive attentions, but its application was drastically suppressed due to low photocatalytic activity. Herein, non-metal heteroatom co-doping is employed to extend the visible light absorption, and regulating morphology into nanosheets promotes the charge separation and transfer. Elements of P/S were successfully introduced into the carbon nitride framework by thermal condensation of their corresponding precursors with melamine. And, the presence of NH4Cl would produce abundant gas to blow CN layers separately to form thin nanosheets. The obtained P/S co-doped carbon nitride nanosheet (g-PSCNNS) sample presents enhanced absorption in visible light region and efficiencies for separation and transport of photo-generated charges. The synergistic effect of elemental co-doping and nanosheet-like morphology endues g-PSCNNS with superior photocatalytic performance for removal of organic pollutants in comparison with the pristine, P or S individual doped and P/S co-doped g-C3N4 samples. Moreover, this g-PSCNNS sample has excellent photocatalytic stability and reusability. Experiments of radical quenching demonstrate superoxide radical is the main active species in the photocatalytic process.

Interconnected nitrogen and sulfur co-doped graphene-like porous carbon nanosheets with high electrocatalytic activity as counter electrodes for dye-sensitized and quantum dot-sensitized solar cells

Interconnected nitrogen and sulfur co-doped graphene-like porous carbon nanosheets (NSGPCSs) are facilely produced by thermal annealing methyl orange (MO) doped polypyrrole (PPy) nanotubes at the presence of KOH under N2 atmosphere at 700 °C. The pyrolysis of PPy combined with the dedoping of PPy nanotubes derived from the interactions between KOH and MO lead to transforming 1D PPy nanotubes into 2D graphene-like carbon nanosheets. The as-prepared NSGPCSs have high specific surface area (up to 1744.98 m2 g−1) and hierarchical porosity, and are investigated as the counter electrodes for dye-sensitized and quantum dot-sensitized solar cells. The unique characteristics such as co-doping of nitrogen and sulfur heteroatoms, high specific surface area, and interconnected graphene-like nanosheets with hierarchical porosity render NSGPCSs a promising electrode material for photoelectrochemical cells. Electrochemical investigations indicate that NSGPCS electrodes display excellent electrocatalytic activity for the regeneration of the I−/I3− and polysulfide electrolytes. As a result, the dye-sensitized solar cell based on NSGPCS electrode achieves a conversion efficiency of 8.21%, which is very close to that of the cell based on conventional Pt electrode (8.61%). The efficiency of the quantum dot-sensitized solar cell assembled with NSGPCS counter electrode is significantly higher than that of the cell assembled with Pt counter electrode, and comparable to that of the cell assembled with PbS counter electrode.

Porphyrin-like Fe-N4 sites with sulfur adjustment on hierarchical porous carbon for different rate-determining steps in oxygen reduction reaction

We developed a strategy based on coordination polymer to synthesize singleatom site Fe/N and S-codoped hierarchical porous carbon (Fe1/N,S-PC). The as-obtained Fe1/N,S-PC exhibited superior oxygen reduction reaction (ORR) performance with a half-wave potential (E1/2, 0.904 V vs. RHE) that was better than that of commercial Pt/C (E1/2, 0.86 V vs. RHE), single-atom site Fe/N-doped hierarchical porous carbon (Fe1/N-PC) without S-doped (E1/2, 0.85 V vs. RHE), and many other nonprecious metal catalysts in alkaline medium. Moreover, the Fe1/N,S-PC revealed high methanol tolerance and firm stability. The excellent electrocatalytic activity of Fe1/N,S-PC is attributed to the synergistic effects from the atomically dispersed porphyrin-like Fe-N4 active sites, the heteroatom codoping (N and S), and the hierarchical porous structure in the carbon materials. The calculation based on density functional theory further indicates that the catalytic performance of Fe1/N,S-PC is better than that of Fe1/N-PC owing to the sulfur doping that yielded different rate-determining steps.

Microporosity‐Controlled Synthesis of Heteroatom Codoped Carbon Nanocages by Wrap‐Bake‐Sublime Approach for Flexible All‐Solid‐State‐Supercapacitors

AbstractHeteroatom‐doped carbon nanomaterials with high surface area and tunable microporosity are important but they generally require difficult and multistep syntheses. Herein, a simple and straightforward strategy is introduced that involves a wrap‐bake‐sublime approach to synthesize microporosity controlled and heteroatom codoped carbon nanocages. A zinc‐containing zeolitic imidazolate framework (ZIF‐8) core is wrapped in a cross‐linked oligomer containing nitrogen and phosphorus, oligo(cyclotriphosphazene‐co‐hexahydroxytriphenylene) (OCHT). As‐synthesized core–shell ZIF‐8‐OCHT nanoparticles are baked at high temperatures to sublimate zinc through OCHT shell, resulting in a porous structure. Meanwhile, hollow cavities are introduced into N,P codoped carbon nanocages (NPCNs) via the sacrificial nature of ZIF‐8 template. The microporosity is finely tuned by controlling thickness of the OCHT shell during synthesis of the core–shell nanoparticles, since the sublimation tendency of zinc component at high temperatures depends on the thickness of OCHT shell. A systematic correlation between the electrochemical performance of NPCNs and their microporosity is confirmed. Furthermore, the electrochemical performance of the NPCNs is related to the degree of heteroatom codoping. The approach is successfully scaled‐up without compromising their electrochemical performance. Finally, a symmetric and flexible all‐solid‐state‐supercapacitor with high energy and power density, and a long‐term cycleability is demonstrated (75% capacitance retention after 20 000 cycles).

An effective FeCl3 template assisted synthesis of nitrogen, sulfur and iron-tridoped carbon nanosheets from a protic salt for oxygen reduction electrocatalysis

Doping heteroatoms into carbon matrix was an efficient strategy to achieve a high-performance non-precious metal oxygen reduction electrocatalyst. Herein, an in situ templated synthesis strategy has been demonstrated to fabricate nitrogen, sulfur and iron-tridoped mesoporous carbon nanosheets (NSFC) with FeCl3 as the two-dimensional template. And a protic salt was used as the carbon, nitrogen and sulfur source, which realized one-step preparation of catalyst materials and the co-doping of various heteroatoms simultaneously. As a result, the optimized NSFC catalyst possessed comparable catalytic activity and selectivity, while superior durability and methanol permeability resistance to commercial 30 wt% Pt/C catalyst in alkaline media. Such excellent performance should be ascribed to the efficient multiple-element doping into the large-specific-surface-area and highly stable carbon nanosheets realized by the in situ synthesis route with a novel FeCl3 template.

Zinc and nitrogen ornamented bluish white luminescent carbon dots for engrossing bacteriostatic activity and Fenton based bio-sensor

Carbon dots with heteroatom co-doping associated with consummate luminescence features are of acute interest in diverse applications such as biomolecule markers, chemical sensing, photovoltaic, and trace element detection. Herein, we demonstrate a straightforward, highly efficient hydrothermal dehydration technique to synthesize zinc and nitrogen co-doped multifunctional carbon dots (N, Zn-CDs) with superior quantum yield (50.8%). The luminescence property of the carbon dots can be tuned by regulating precursor ratio and surface oxidation states in the carbon dots. A unique attribution of the as-prepared carbon dots is the high monodispersity and robust excitation-independent emission behavior that is stable in enormously reactive environment and over a wide range of pH. These N, Zn-CDs unveils captivating bacteriostatic activity against gram-negative bacteria Escherichia coli. Furthermore, the excellent luminescence properties of these carbon dots were applied as a platform of sensitive biosensor for the detection of hydrogen peroxide. Under optimized conditions, these N, Zn-CDs reveals high sensitivity over a broad range of concentrations with an ultra-low limit of detection (LOD) indicating their pronounced prospective as a fluorescent probe for chemical sensing. Overall, the experimental outcomes propose that these zero-dimensional nano-dots could be developed as bacteriostatic agents to control and prevent the persistence and spreading of bacterial infections and as a fluorescent probe for hydrogen peroxide detection.

A dyeing-induced heteroatom-co-doped route toward flexible carbon electrode derived from silk fabric

Flexible carbon electrode with high performance from silk fabric was fabricated by a simple approach. Silk fabric was uniformly dyed with heteroatom-enriched dye molecules by a traditional dyeing process, followed by direct pyrolysis. The as-prepared heteroatom-co-doped carbonized silk fabric exhibits a significantly improved electrochemical performance with the specific capacitance of 255.95 F g−1 at the scan rate of 2 mV s−1 using 1 M Na2SO4 electrolyte, a wide operation voltage window as well as a good cycling life stability (8% capacitance loss over 5000 cycles). The excellent capacitive performance can be attributed to the multiple synergistic effects between the double-layer capacitance (hierarchical porosity, good wettability and conductivity) and the extra pseudocapacitance (N, O and S heteroatom co-doping). Moreover, the carbonized dyed silk fabric possesses wearability and lightweight. Importantly, the convenient approach can provide industrial-grade production of heteroatom-co-doped silk fabric-based carbon electrode materials for applications in flexible energy storage devices.

Three-dimensional nitrogen and phosphorous Co-doped graphene aerogel electrocatalysts for efficient oxygen reduction reaction

The development of efficient electrocatalysts for oxygen reduction reaction (ORR) is of importance for fuel cells and metal-air batteries. Herein, three-dimensional nitrogen and phosphorous co-doped graphene aerogel (NPGA) was prepared via the pyrolysis of polyaniline (PANi) coated graphene oxide aerogel synthesized by oxidative polymerization of aniline on graphene oxide (GO) sheets in the presence of phytic acid. The uniform coating of PANi thin layer on the surface of GO sheets enables the formation of highly porous composite aerogel of PANi and GO. The subsequent thermal treatment is able to prepare the porous NPGA due to the carbonization of PANi and phytic acid as nitrogen and phosphorous resources. When used as electrocatalysts, the as-prepared NPGA electrocatalysts exhibited good catalytic activity to ORR via an efficient four-electron pathway with good stability, benefiting from the highly porous structure and the heteroatom co-doping. More importantly, Zn-air batteries operated in ambient air have been fabricated by coupling a Zn plate with the NPGA electrocatalyst in an air electrode, demonstrating the maximal power density as high as ~260 W/g and a good long-term stability with slightly potential decay for over 450 h. The facile method for preparing efficient carbon based ORR electrocatalysts would generate other potential applications including fuel cells and others.