In-situ synthesis of N/S co-doped Cu-based graphene-like nanosheets as high efficiency electrocatalysts for oxygen reduction reaction

Heteroatom-doped transition metal electrocatalysts supported on carbon materials are widely-recognized as the promising catalysts for oxygen reduction reaction (ORR). Here, we describe the one-pot method of preparing the Cu-based PAT₁-Cu_x/KB catalyst with Cu/N/S doped graphene-like nanosheets. For the obtained catalyst, Cu²⁺ ions catalyzed the polymerized 2-aminothiazole organic monomers into nanosheet and simultaneously in-situ doped Cu, N, S atoms into the carbon matrix. The amount of Cu²⁺ ions affected the geometry structure, as well as the formation of Cu–N structure and C–S–C bond of PAT₁-Cu_x/KB catalyst. Cu₂S crystals with ORR catalytic ability were also generated in the catalysts. The Cu–N structure in the catalyst regulates the d-electron density of inert copper through the synergistic effect of electronic connection between copper and nitrogen atoms. N and S doped in the carbon skeleton changes the spin density and charge distribution of near carbon atoms. Therefore, PAT₁-Cu_0.33/KB catalyst with graphene-like nanosheets, Cu–N structure, C–S–C bond, and Cu₂S crystals exhibits excellent activities with E_1/2 = 0.84 V and high limit-current density of 5.25 mA cm⁻² for ORR.     

Agaricus bisporus residue-derived Fe/N co-doped carbon materials as an efficient electrocatalyst for oxygen reduction reaction

Biomass-derived multielement-co-doped carbon materials with ultrahigh active-sites density and unique physicochemical properties hold great promise for oxygen reduction reaction (ORR) in fuel cells and metal-air batteries. Agaricus bisporus residue as a type of biomass waste is produced after microbial growth on biomass substrates, contributing to its natural multidimensional framework and nutrient elements residual. Based on this advantage, this paper further combined with (NH₄)₃PO₄ and FeCl₃·6H₂O to provide N, P, and Fe. Finally, the Fe/N co-doped carbon catalyst with hierarchical porous structure (SN-Fe-ZA) was fabricated by a facile hydrothermal-pyrolysis synthesis route. The characteristic of SN-Fe-ZA exhibited an obvious honeycomb porous structure, high nitrogen doping content of 2.36 at%, and its specific surface area was up to 1646.4 m²·g⁻¹ with abundant micro-/mesoporous. Electrochemical measurements further indicated that SN-Fe-ZA possessed a distinct ORR electrocatalytic activity in alkaline solution. Compared with the electrochemical parameters of commercial Pt/C electrocatalyst, SN-Fe-ZA had the equivalent onset potential (0.968 V) and half-wave potential (0.820 V). Besides, it showed a more excellent electrochemical stability and stronger methanol-tolerant. This research proposed a promising approach to prepare hierarchical porous and multielement-co-doped catalyst from renewable biomass waste as effective cathode electrocatalytic materials for alkaline fuel cells.     

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

The economical, efficient and durable oxygen reduction catalysts facilitate the enhancement of electrochemical energy devices competitiveness towards widespread applications. In view of this, we provide an innovative sulfuration inducing method for the synthesis of ZnS and cobalt nanoparticles decorated N, S co-doped CNTs (ZnS/Co-NSCNTs) catalyst. S introduced into the zinc-based zeolitic imidazolate frameworks (ZIF-8) and cobalt-based zeolitic imidazolate frameworks (ZIF-67) precursors via pyrolysis, and induced the generation of ZnS/Co-NSCNTs have been confirmed by XRD, SEM, TEM, and XPS techniques. The key features including activity sites, transfer channels and adsorption energy back up the excellent electrocatalytic activity of the as-prepared ZnS/Co-NSCNTs towards oxygen reduction reactions (ORR). ZnS/Co-NSCNTs additionally exhibited a positive half-wave potential of 0.871 V (vs. RHE) with improved current density towards ORR. In alkaline medium, ZnS/Co-NSCNTs catalyst displayed a high tolerance towards methanol and an excellent long-term cycling stability. The observed onset potential for our prepared ZnS/Co-NSCNTs catalyst is analogous with the commercially available noble metal catalysts. Also, ZnS/Co-NSCNTs catalyst as a cathode in zinc-air battery displayed an enhanced electrochemical performance with a highly specific capacity of 750.1 mAh g⁻¹, outstanding cycling stability, and high rate behavior. This work provides a new approach for the construction of stable low-cost alternative air-cathode catalysts for other energy conversion and storage applications.     

Fe3C nanoparticles decorated Fe/N codoped graphene-like hierarchically carbon nanosheets for effective oxygen electrocatalysis

Hierarchically porous carbon sheets decorated with transition metal carbides nanoparticles and metal-nitrogen coordinative sites have been proposed as the promising non-precious metal oxygen electrocatalysts. In this work, we demonstrate a facile and low-cost strategy to in situ form Fe/N codoped hierarchically porous graphene-like carbon nanosheets abundant in Fe-N_x sites and Fe₃C nanoparticles (Fe–N/C) from pyrolyzing chestnut shell precursor. The as-prepared Fe–N/C samples with abundant Fe-N_x sites and Fe₃C nanoparticles show superior electrocatalytic activity to oxygen reduction reaction (ORR) in the alkaline medium as well as high stability and methanol tolerance due to the integration of multi-factors: the high content of Fe-N_x active sites, the coexistence of Fe₃C, the unique hierarchically porous structure and high conductivity of carbon matrix. The optimal Fe–N/C-2-900 sample exhibits a more positive half-wave potential (−0.122 V vs. Ag/AgCl (3 M) reference electrode) than commercial 20 wt% Pt/C catalyst. This study provides a facile approach to synthesize Fe₃C nanoparticles decorated Fe/N co-doped hierarchically porous carbon materials for effective oxygen electrocatalyst.     

One-step carbonization of ZIF-8 in Mn-containing ambience to prepare Mn,N co-doped porous carbon as efficient oxygen reduction reaction electrocatalyst

Economical and efficient non-noble metal catalysts should be developed practically, instead of commercial Pt/C for fuel cells. In this paper, manganese, nitrogen co-doped porous carbon (Mn–N–C) was synthesized to catalyze oxygen reduction reaction (ORR) through the one-step carbonization of ZIF-8 in the Mn-containing (MnCl₂) atmosphere. During the carbonization process, MnCl₂ gas was captured with ZIF-8 and then transformed into uniform Mn–N active sites distributed in the porous carbon materials. The Mn–N–C catalyst exhibited plentiful porous structures, large specific surface areas, high graphitization and conductivity, which contributed to the transfer and transport of charge and exposed more active sites. The Mn–N–C catalyst exhibited superior catalytic ability in alkaline and acidic solutions. Half-wave potential of the Mn–N–C could reach 0.88 and 0.73 V in 0.1 M KOH and 0.5 M H₂SO₄, respectively. In addition, the Mn–N–C catalyst showed a prominent stability after the stability test of 18,000 s. Excellent electrochemical performance and endurance make the Mn–N–C expect to be an effective ORR catalyst to build high-performance fuel cells.     

Flame synthesis of nitrogen,boron co-doped carbon as efficient electrocatalyst for oxygen reduction reaction

The flame synthesis provides a simple low-cost method to produce novel carbon materials. In this study, N, B co-doped carbon (NBC) materials have been prepared by flame synthesis. Among many as-prepared samples, the NBC catalyst which prepared under carbonization temperature of 1000 °C for 3 h with acetonitrile/acetone precursor of 1:1 exhibits the best catalytic activity and stability, as well as good resistance to methanol interference for oxygen reduction reaction (ORR), with half-wave potential being almost nearly to Pt/C, and a quasi-four-electron transfer process. This study would provide an economic, environmental feasible and scalable approach for fabricating novel heteroatom co-doped carbon materials for ORR applications.     

Tunable Fe/N co-doped 3D porous graphene with high density Fe-Nx sites as the efficient bifunctional oxygen electrocatalyst for Zn-air batteries

Nitrogen-doped transition metal materials display promising potential as bifunctional electrocatalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Herein, Fe/N co-doped three-dimensional (3D) porous graphene (FeN-3D-PG) is prepared via a template method using sodium alginate as the carbon source and low polymerization degree melamine resin as the nitrogen source. The low polymerization degree melamine resin can form complexes with Fe³⁺ in the aqueous solution and further forms high density Fe-N_x active sites during pyrolysis. Meanwhile, the formed 3D porous structure efficiently promotes the uniform distribution of Fe-N_x active sites. The FeN-3D-PG catalyst exhibits pH-independent ORR activity. For OER, the catalyst possesses a low over potential (370 mV at 10 mA cm⁻²) in alkaline electrolyte. The Zn-air batteries (ZABs) using FeN-3D-PG as cathode exhibits a power density up to 212 mW cm⁻², a high specific capacity of 651 mAh g⁻¹, and the charge-discharge stability of 80 h. This work provides new sight to transition metal materials based ZABs with excellent performance.     

An efficient metal-free bifunctional oxygen electrocatalyst of carbon co-doped with fluorine and nitrogen atoms for rechargeable Zn-air battery

It is highly critical to explore efficient bifunctional oxygen electrocatalysts for regenerative fuel cells and metal-air batteries. Herein, N, F co-doped carbon material (NF@CB) was synthesized as metal-free efficient bifunctional electrocatalysts by directly pyrolyzing a mixture of carbon black, polytetrafluoroethylene and melamine. Benefiting from the synergistic effects between N and F atoms, NF@CB exhibits a positive half-wave potential (E_1/2) of 0.814 V (vs. RHE) for oxygen reduction reaction, and an operating potential (E₁₀) of 1.609 V at 10 mA cm⁻² for oxygen evolution reaction in alkaline electrolyte. The bifunctional oxygen electrocatalytic activity index (ΔE = E₁₀−E_1/2) is 0.795 V, which is notably better than that of the single N-doped carbon (1.238 V), and similar to that of the commercial Pt/C and RuO₂ mixture catalyst (0.793 V). Impressively, the assembled Zn-air battery (ZAB) with NF@CB as an air-electrode catalyst displays a small charge/discharge voltage gap of 0.852 V at 20 mA cm⁻². Moreover, the NF@CB catalyzed ZAB exhibits good rechargeability and long-lasting cycling stability with over 49 h. This investigation introduces a cheap and simple way to develop highly efficient bifunctional N, F co-doped electrocatalysts.     

High performance biomass-derived catalysts for the oxygen reduction reaction with excellent methanol tolerance

The discovery of low cost and efficient catalytic materials for the oxygen reduction reaction (ORR) is of paramount importance for industrial-scale fuel cell manufacture. In this work, a convenient and straightforward approach was designed and applied to produce iron and nitrogen co-doped biomass carbon/graphene composite (Fe–N/C_B-RGO) by using soybean dregs combined with graphene oxide (GO). The results show that the optimized Fe–N/C_B-RGO (1) sample has high catalytic activity and stability for ORR, the onset potential of Fe–N/C_B-RGO (1) is 0.02 V vs. Hg/HgO, which is merely 50 mV negative-shifted comparison with commercial Pt/C. The composition optimized Fe–N/C_B-RGO (1) catalyst showed excellent methanol tolerance, with the presence of methanol surprisingly improving ORR performance. This unique catalytic performance of the Fe–N/C_B-RGO (1) catalyst is attributed to electron transfer synergies arising from close interfacial contact between the biomass-derived carbon and graphene.     

Three-dimensional urchin-like N/S co-doped Mn-based metal-organic frameworks for efficiently enabling oxygen reduction reaction

The exploration of economical and effective non-noble metal catalysts is essential for oxygen reduction reaction (ORR) in energy devices. Recently, heteroatom-doped metal-organic frameworks (MOFs) have shown great potential in ORR due to their high efficiencies and low costs. Herein, three-dimensional (3D) urchin-like N/S co-doped Mn-based MOFs (U–N/S–Mn-MOFs) as an effective ORR catalyst have been successfully prepared by a facile one-step solvothermal methodology. The unique 3D urchin-like structure with a spherical interior and dendritic exterior may provide more catalytic sites and transport channels for ORR. Simultaneously, the doped N and S combined with Mn can promote oxygen adsorption and reduce the reaction energy barrier. These characteristics endow U–N/S–Mn-MOFs with high ORR performance. The present work provides a new opportunity for multiple heteroatom-doped MOFs to achieve high electrocatalytic performance.     

Synthesis of a N-doped mesoporous carbon as an efficient electrocatalyst for oxygen reduction

A facile and effective approach was developed for the preparation of mesoporous Fe-NC by pyrolyzing the mixture of FeCl₂, urea, (NH₄)₂MoO₇, phthalic anhydride and SBA-15, during which the in-situ formation of iron phthalocyanine is confirmed. The obtained catalyst exhibits high catalytic activity towards ORR, whose half-wave potential can be 53 mV more positive than that of commercial Pt/C catalyst. Besides, the catalyst also exhibits high selectivity of four electron path, along with excellent stability and methanol tolerance in alkaline media. Based on the characterization results, we suggest, the higher surface areas, highly porous structures induced by SBA-15 addition, as well as high graphitic N content should be the proper origins for its outstanding catalytic performance.     

S,N co-doped graphene quantum dots decorated TiO2 and supported with carbon for oxygen reduction reaction catalysis

Sluggish kinetics and catalyst instability in oxygen reduction reaction are the central issues in fuel cell and metal-air battery technologies. For that, highly active, stable, and low-cost non-platinum based electrocatalysts for oxygen reduction reaction are an immediate requirement in fuel cell and metal-air battery technologies. A new composite (S,N-GQD/TiO₂/C-800) is synthesized, made of sulfur (S) and nitrogen (N) co-doped graphene quantum dot (GQD) with TiO₂. This composite is supported on carbon on heating at 800 °C under N₂ atmosphere and is explored for oxygen reduction reaction (ORR) catalyst. The synthesized composite S,N-GQD/TiO₂/C-800, shows outstanding catalytic activity with an onset potential of 0.91 V and a half-wave potential of 0.82 V vs. RHE, an alkaline medium. The Tafel slope of the catalyst is 61 mV dec^?1. The catalyst is an excellent methanol tolerant and shows good stability in an alkaline medium. The excellent ORR activity of S,N-GQD/TiO₂/C-800 is ascribed to well-built interactivity between the S,N-GQD/TiO₂, and the carbon support. The unique structure offers advantages, with outstanding electrical conductivity, high surface area, and excellent charge transfer kinetics between the doped GQD and TiO₂ interface and subsequently from the carbon surface to the S,N-GQD/TiO_2.     

A dual ligand coordination strategy for synthesizing drum-like Co,N co-doped porous carbon electrocatalyst towards superior oxygen reduction and zinc-air batteries

We herein propose a dual ligand coordination strategy for deriving puissant non-noble metal electrocatalysts to substitute valuable platinum (Pt)-based materials toward oxygen reduction reaction (ORR), a key reaction in metal-air batteries and fuel cells. In brief, cobalt ions are firstly double-coordinated with proportionate 2-methylimidazole (2-MeIm) and benzimidazole (BIm) to obtain drum-like zeolitic imidazolate frameworks (D-ZIFs), which are then carbonized to output the final Co, N co-doped porous carbon (Co–N–PC_D) catalyst inheriting the drum-like morphology of D-ZIFs. The Co–N–PC_D is featured by mesopores and exhibits superb electrocatalytic behavior for ORR. Impressively, the half-wave potential of Co–N–PC_D catalysts is 0.886 V with finer methanol-tolerance and stability than those of commercial Pt/C. Additionally, a zinc-air battery assembled from the Co–N–PC_D displays an open-circuit voltage of 1.413 V, comparable to that of commercial Pt/C (1.455 V), suggesting the potentials of Co–N–PC_D in practical energy conversion devices.     

A novel in-situ strategy develops for Mo2C nanoparticles incorporated on N,P co-doped stereotaxically carbon as efficient electrocatalyst for overall water splitting

Developing cost-effective and remarkable electrocatalysts toward oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) performs excelling role in boosting the hydrogen energy application. Herein, a novel in-situ one-pot strategy is developed for the first time to synthesize molybdenum carbide nanoparticles (Mo₂C NPs) incorporated on nitrogen (N) and phosphorous (P) co-doped stereotaxically carbon (SC). The optimized Mo₂C NPs/N, P–SC–800 electrocatalyst exhibits lower overpotentials of 131 and 287 mV for HER and OER to deliver a current density of 10 mA cm^?2 in 1.0 M KOH medium with smaller Tafel slopes of 58.9 and 74.4 mV/dec, respectively. In addition, an electrolyzer using Mo₂C NPs/N, P–SC–800 electrode as cathode and anode delivers a current density of 10 mA cm^?2 at a small voltage of 1.64 V for overall water splitting. The excellent water splitting performance could be ascribed to optimum Mo₂C NPs for more accessible active sites, highly active N, P-SC networks for accelerated electron transfers, and synergetic effect between Mo₂C NPs and N, P-SC networks. The N, P-SC network not only enhances the overall dispersion of Mo₂C NPs but also contributes numerous electroactive edges to enhance the performance of HER, OER, and overall water splitting activity. This research work explores the in-situ one-step strategies of advanced, cost-effective, and non-precious metal electrocatalysts for efficient water splitting and motivates the consideration of a novel class of heteroatom doped stereotaxically carbon nanocomposites for sustainable energy production.     

Fe and N co-doped carbon derived from melamine resin capsuled biomass as efficient oxygen reduction catalyst for air-cathode microbial fuel cells

Cathode oxygen reduction reaction (ORR) performance is crucial for power generation of microbial fuel cells (MFCs). The current study provides a novel strategy to prepare Fe/N-doped carbon (Fe/N/C) catalyst for MFCs cathode through high temperature pyrolyzing of biomass capsuling melamine resin polymer. The obtained Fe/N/C can effectively enhance activity, selectivity and stability toward 4 e^– ORR in pH neutral solution. Single chamber MFC with Fe/N/C air cathode produces maximum power density of 1166 mW m⁻², which is 140% higher than AC cathode. The improved performance of Fe/N/C can be attributed to the involvement of nitrogen and iron species. The excellent stability can be attributed to the preferential structure of the catalyst. The moderate porosity of the catalyst facilitates mass transfer of oxygen and protons and prevents water flooding of triple-phase boundary where ORR occurs. The biomass particles encapsulated in the catalyst act as skeletons, which prevents catalyst collapse and agglomeration.     

Ordered distributed nickel sulfide nanoparticles across graphite nanosheets for efficient oxygen evolution reaction electrocatalyst

Low-cost and earth-abundant nickel chalcogenides with versatilities in electrocatalysis, conversion and storage of energy are hindered in practical application due to the low electrical conductivity and small specific surface area. In the present work, we report a simple preparation of 2D nanocomposites of NiS_x (5 nm) uniformly embedded in several layered graphite (NiS_x@graphite) through the sulfidation of nickel naphtalenedicarboxylic acid framework nanosheets (∼9 nm). The obtained NiS_x@graphite nanosheet composites are used for oxygen evolution reaction (OER) catalysis. Electrochemical studies reveal that their OER activities under strongly alkaline conditions are ranked in the order of Ni₉S₈@graphite > NiS@graphite > NiS₂@graphite. The outstanding OER performance offered by Ni₉S₈@graphite owes to the synergistic effects of large specific surface area and the special structure between nickel sulfide and graphite layer, and the intrinsic large TOFs and the optimal adsorption energy of Ni₉S₈. Furthermore, Ni₉S₈@graphite as an anode material used for lithium ion batteries (LIBs) also shows a high specific capacity with competitive rate performance. Such excellent performance and low price render nickel chalcogenides a promising candidate for the future OER catalyst and LIBs application.     

Synthesis of MoS2 nanoparticles embedded,N, S co-doped mesoporous carbon via molten salt method as hydrogen evolution electrocatalyst under alkaline and neutral conditions

We developed a salt-template strategy to prepare MoS₂ nanoparticles (NPs) embedded, N, S co-doped carbons via the solid-state process. The addition of the inorganic salt played two main roles in the synthetic proceeding. First, the salts could be utilized as the templates to produce the mesopores, which could be removed by simple washing process. Second, the salts could promote the formation of MoS₂ NPs. The as-received electrocatalyst, K-G4.0T2.0Mo1.0, possessed high BET surface area of 446 m² g^?1, in addition to high double layer capacitance of 24.5 mF cm^?2 in the alkaline media. When evaluated as the electrocatalyst for hydrogen evolution reaction (HER), K-G4.0T2.0Mo1.0 demonstrated excellent performance in the alkaline and neutral medias. In details, K-G4.0T2.0Mo1.0 showed a low overpotential of 173 and 358 mV to afford 10 mA cm^?2 under alkaline and neutral conditions, respectively, as well as outstanding durability.     

Fe2O3 nanoparticles immobilized on N and S codoped C as an efficient multifunctional catalyst for oxygen reduction reaction and overall water electrolysis

Currently, multifunctional electrocatalysts with superior performance are very vital for developing various clean and regenerated energy systems. Herein, an effective multifunctional electrocatalyst comprising Fe₂O₃ nanoparticles immobilized on N and S codoped C has been synthesized via heat-treatment of Fe(II) complex at 800 °C (denoted as Fe₂O₃/NS-C-800). Favorable features including the introduction of maghemite nanoparticles, N/S-codoping effect, and close contact between the Fe₂O₃ nanoparticles and NS-C ender the Fe₂O₃/NS-C-800 with high multifunctional catalytic performance. The onset potential (0.97 V) and half-wave potential (0.81 V) of the Fe₂O₃/NS-C-800 towards oxygen reduction reaction (ORR) are comparable to Pt/C (0.99 and 0.82 V). The Fe₂O₃/NS-C-800 also exhibits high oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) activity with low OER and HER overpotentials of 0.37 and −0.27 V at 10 mA cm⁻², respectively. In addition, higher ORR, OER and HER stabilities than Pt/C are observed for the Fe₂O₃/NS-C-800. More importantly, the assembled water electrolyzer using the Fe₂O₃/NS-C-800 as the anode and cathode exhibits a high stability at a water electrolysis current density of 10 mA cm⁻². The present study offers a new promising non-noble multifunctional catalyst for future application in renewable energy technologies.     

Molten salt strategy to synthesize alkali metal-doped Co9S8 nanoparticles embedded,N, S co-doped mesoporous carbon as hydrogen evolution electrocatalyst

A molten salt strategy was proposed to prepare a series of electrocatalysts for hydrogen evolution reaction (HER) with salts as templates, which consisted of Co₉S₈ nanoparticles (NPs) and N, S co-doped mesoporous carbons. The porosities, heteroatoms contents, and crystalline structures of the final electrocatalysts were determined by the types of salts and the calcining temperatures. When KCl/NaCl, KCl/LiCl, and NaCl/CaCl₂ were adopted as the molten salts, Co₉S₈ NPs embedded, N, S co-doped carbons were obtained. However, when CaCl₂ and ZnCl₂ were used as the molten salts, Co₉S₈ could not be synthesized. The characterization results exhibited that alkali metal atoms could be introduced in the lattices of Co₉S₈. The combination of experimental and theoretical results revealed that Na and K atoms doping improved the electrocatalytic performance for HER. GTCo900-KCl/NaCl possessed the best HER activity, delivering a current density of 10 mA cm⁻² at 54 mV in acidic media, 142 mV in neutral media, and 103 mV in alkaline media.     

Facile synthesis of boron and nitrogen-doped graphene as efficient electrocatalyst for the oxygen reduction reaction in alkaline media

Boron-doped graphene and nitrogen-doped graphene have been respectively synthesized by a facile thermal solid-state reaction of graphene oxide with boric acid and urea. The morphology and structure of the doped graphene have been characterized by the scanning electron microscopy, infrared spectroscopy, ultraviolet visible spectroscopy and X-ray photoelectron spectroscopy, while the electrocatalytic activity toward oxygen reduction reaction has been evaluated by the cyclic voltammetry. It has been shown that the morphology, structure, doping level and fashions of graphene could be finely tuned by the thermal treatment conditions, and which have substantial effects on the activity of oxygen reduction reaction. The boron-doped graphene and nitrogen-doped graphene calcined at 700 °C demonstrate excellent electrocatalytic oxygen reduction activities as the appropriate introduction of boron and nitrogen functional groups in graphene, which might be promising for low temperature fuel cell applications.