Nitrogen doped amorphous carbon as metal free electrocatalyst for oxygen reduction reaction

A non metal catalyst for the oxygen reduction reaction is prepared by simply pyrolyzing ion exchange resin D113 in NH₃. The product is nitrogen doped amorphous carbon. The pyrolysis of D113 exchanged with iron ion results in nitrogen doped graphitic carbon. The amorphous carbon is easier to be doped by NH₃ with higher nitrogen content. The nitrogen doped amorphous carbon is more active than graphitized carbon, together with much improved stability. The higher activity is explained by the higher total nitrogen content and higher pyridinic/graphitic nitrogen percentage. The higher stability is because there is no loss or dissolution of the active sites. The results of this work prove metal element and graphitization of carbon are not necessary factors for nitrogen doped carbon as non noble metal catalyst for the oxygen reduction reaction.     

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.     

Fe2O3-encapsulated and Fe-Nx-containing hierarchical porous carbon spheres as efficient electrocatalyst for oxygen reduction reaction

It is highly desirable to develop high-efficiency non-precious electrocatalysts toward oxygen reduction reaction (ORR). In this work, Fe₂O₃-encapsulated and Fe-Nx-containing porous carbon spheres (Fe₂O₃/N-MCCS) with unique multi-cage structures and high specific surface area (1360 m² g^?1) are fabricated. The unique porous structure of Fe₂O₃/N-MCCS ensures fast transportation of oxygen during ORR. The combined effect of Fe₂O₃ nanoparticles and Fe-Nx configurations endows Fe₂O₃/N-MCCS (E_1/2 = 0.837 V vs. RHE) with superior ORR activity and methanol tolerance to Pt/C. And, Fe₂O₃/N-MCCS exhibits better stability than nitrogen-modified carbon. The characterization results of Fe₂O₃/N-MCCS after long-term test reveals its excellent structural stability. Impressively, zinc-air battery based on Fe₂O₃/N-MCCS showed a peak power density of 132.4 mW cm^?2 and a specific capacity of 797 mAh g^?1, respectively.     

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.     

Oxidized carbon/nano-SiC supported platinum nanoparticles as highly stable electrocatalyst for oxygen reduction reaction

Nano-SiC particles with derived carbon shells were prepared by an acid-etching method at room temperature. The mixture solutions of concentrated HF and HNO₃ were chosen to etch the nano-SiC particles, and an amorphous carbon shell absorbed by oxygen functional groups was formed on the SiC surface. The oxidized carbon/SiC (O-C/SiC) particles were used as supports for preparation of Pt electrocatalysts. The O-C/SiC supported Pt electrocatalysts showed a high catalytic activity and an excellent stability for oxygen reduction reaction. The improved stability can be ascribed to the anchoring effect of the carbon shell to Pt NPs and the high stability of nano-SiC core.     

Electrosynthesis of Mn-Fe oxide nanopetals on carbon paper as bi-functional electrocatalyst for oxygen reduction and oxygen evolution reaction

A layered binary Mn-Fe oxide as bi-functional electro-catalyst with nanopetals morphology is grown on porous carbon paper for the first time via one-step electrodeposition process. The electrocatalyst is characterized by X-ray diffraction, scanning electron microscopy (SEM) and energy dispersive spectroscopy analysis. SEM analysis demonstrates notable morphology viz. nanopetals of the Mn-Fe oxide grown on carbon paper. The electrocatalytic activity is checked for both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) in alkaline medium. Rotating disk electrode (RDE) voltammetry is carried out to study the ORR kinetics, which proves that ORR process follows four-electron pathway in alkaline medium. Oxygen evolution reaction study reveals that it has higher activity for OER with a lower onset potential of 1.6 V vs RHE and higher current density of 11.5 mA/cm² at 2.0 V vs RHE reference electrode.     

Interrelations between sulfur,iron, nitrogen,pore and graphite matrix for oxygen reduction reaction

Nitrogen doped lotus-stem carbon and that being promoted by sulfur or iron (N-LC, NS-LC, NFe-LG and NSFe-LG) are synthesized. The interrelations between pore size, graphitization degree, N content, Fe–N content, S doping, and their effects on oxygen reduction reaction (ORR) activity and stability in alkaline media are studied. The NSFe-LG shows the most excellent performances for ORR. The Fe-free NS-LC shows close ORR activity and comparable stability to the NSFe-LG, which may make metal-free catalyst attractive.     

Se-doped cobalt oxide nanoparticle as highly-efficient electrocatalyst for oxygen evolution reaction

Electrolysis of water has been one of the most promising approaches for renewable energy resources while the efficient oxygen evolution reaction (OER) remains challenging. Herein, a series of different ratio of Se doped Co₃O₄ nanoparticles XSe-Co₃O₄ are prepared by hydrothermal method and applied as OER electrocatalysts. Se^2? is doped into the Co₃O₄ crystal lattice by substituting of O^2? and a large number of oxygen vacancies are generated, which provides more available activity sites for OER. Se doping increases the surface ratio of Co²⁺/Co³⁺ and accelerates the electron transport that favors OER activity promotion. The optimized doping ratio of 6%Se–Co₃O₄ presents low overpotential of 281 mV at 10 mA cm^?2, as well as a low Tafel slope of 70 mV dec^?1 in 1 M KOH solution, which has great advantages compared to the recently reported Co₃O₄-based OER electrocatalysts. This work provides new ideas for the development of efficient Co₃O₄-based OER electrocatalysts.     

Waste wine mash-derived doped carbon materials as an efficient electrocatalyst for oxygen reduction reaction

Oxygen reduction reaction (ORR) is a core reaction of fuel cell and metal-air cell. In recent years, it has been a hot topic to study non-precious metal catalysts for ORR. Herein, we have used waste wine mash-derived carbon, melamine and ferric chloride to prepare a Fe- and N- co-doped carbon catalyst. The specific surface area of the catalyst is up to 1066.6 m² g⁻¹. And its wave potential is 15 mV higher than that of commercial Pt/C catalyst. The ORR on our catalyst followed a four-electron pathway; and it has high stability and high impressive immunity to methanol. After continuous oxygen reduction of 30,000s, the retention rate is 90%.     

Cobalt,sulfur, nitrogen co-doped carbon as highly active electrocatalysts towards oxygen reduction reaction

Rational design of efficient, cost-effective electrocatalyst towards oxygen reduction reaction (ORR) is of vital importance to the wide application of polymer electrolyte membrane fuel cells. In this work, a novel and simple Na₂SO₄-assisted pyrolysis strategy with ZIF-12 as the precursor is reported for the synthesis of cobalt, sulfur, nitrogen, co-doped carbon (termed as CoSNC-xNa₂SO₄-T) materials towards ORR. Different from CoNC-800 derived from pure ZIF-12, with the presence of Na₂SO₄, the derived CoSNC-0.5Na₂SO₄-800 material exhibits layered flake morphology with hierarchical meso-microporous structure. Besides, CoSNC-0.5Na₂SO₄-800 material shows higher content of pyridinic-N and graphitic-N, higher relative intensity of Co-N_x, higher content of carbon defect, as well as larger specific surface area in comparison with CoNC-800, which results in higher activity of CoSNC-0.5Na₂SO₄-800. The CoSNC-0.5Na₂SO₄-800 material displays a half-wave potential of 0.88 V, which is superior to that of commercial Pt/C (half-wave potential being 0.86 V). Moreover, CoSNC-0.5Na₂SO₄-800 demonstrates a better durability compared with Pt/C. The pyrolysis temperature and the amount of Na₂SO₄ are found to affect the physiochemical properties and electrochemical performance of the CoSNC-xNa₂SO₄-T materials. This work not only provides a facile and novel synthesis approach for the preparation of highly active Co, S, N co-doped carbon materials for ORR, but also disclosing the key structure properties for enhancing the performance of these catalysts.     

Spindle-shaped CeO2/biochar carbon with oxygen-vacancy as an effective and highly durable electrocatalyst for oxygen reduction reaction

Highly durable and active CeO₂ on biochar carbon (CeO₂/BC) derived from Spirulina platensis microalgae and synthesized by simple one-pot hydrothermal treatment and further activated through pyrolysis approach. A spindle-shaped morphology of CeO₂ with predominant (111) facet was evidently observed from X-ray diffraction patterns and electron microscopy images. The structural features such as high specific surface area, defect-rich carbon with N & P atoms, increased oxygen vacancy and π-electron transfer play an important role for the improved oxygen reduction reaction (ORR). The considerable amount of Ce³⁺ and higher proportion of pyridinic N and graphitic N species are substantially contributed to the superior ORR performance of CeO₂/BC700, which surpasses other similar catalysts and competing with Pt/C. Hence, the significant kinetic ORR parameters and extended stability (no loss after 5000 potential cycles) of the CeO₂/BC700 catalysts provides the promising insight to develop the rare-earth metal oxide nanostructures as a possible candidate for ORR in alkaline medium.     

Fe doped metal organic framework (Ni)/carbon black nanosheet as highly active electrocatalyst for oxygen evolution reaction

To alleviate the sluggish oxygen evolution reaction (OER) kinetics, it's urgent to develop electrocatalysts with high activity and low cost. In this work, Fe doped metal organic frameworks (Ni)/carbon black composites were synthesized via a facile hydrothermal method. Benefiting from the direct use of metal organic frameworks (MOFs) for OER, numerous and highly dispersed active sites are exposed to the electrolyte and reactants. By regulating Ni/Fe ratios, a high electrochemical active surface area (ECSA) and high relative surface content of active Ni³⁺ species are obtained, which mainly contribute to the high OER activity. Besides, the introduced carbon black (CB) was found to enhance the charge-transfer efficiency of the electrocatalysts, which is also favorable for OER. The optimal Ni9Fe1-BDC-0.15CB electrocatalyst shows excellent OER activity with the low overpotential of ~290 mV at 10 mA cm⁻² and the Tafel slope of ~76.1 mV dec⁻¹, which is comparable to RuO₂ and other MOFs-based OER electrocatalysts reported in recent years.     

Nanoporous PdFe alloy as highly active and durable electrocatalyst for oxygen reduction reaction

Nanoporous PdFe (NP-PdFe) alloy with uniform structure size and controllable bimetallic ratio was easily fabricated by one-step mild dealloying from PdFeAl precursor alloy. NP-PdFe consisted of nanoscaled interconnected network skeleton with bicontinuous hollow channels extending in all three dimensions. Compared with NP-Pd and commercial Pt/C catalysts, the NP-PdFe exhibits superior electrocatalytic activity for oxygen-reduction reaction (ORR) with enhanced specific and mass activities. Electrocatalytic measurements indicated that NP-PdFe possesses higher catalytic durability than Pt/C with the less loss of ORR activity and electrochemical active surface area upon long term potential scan. NP-PdFe alloy also shows higher methanol tolerance relative to Pt/C catalyst. XPS and DFT calculations suggest that the downshift of Pd d-band center after alloying with Fe makes favorable reaction kinetics for ORR with decreased adsorption energy of O and OH on Pd surface.     

Porous carbonized egg white as efficient electrocatalyst for oxygen reduction reaction

Hierarchical porous carbonized egg white (EW) is synthesized and used as oxygen reduction reaction (ORR) catalyst. The typical EW that is carbonized at 650 °C (EW-650) possesses ultrahigh specific surface area of 1904 m² g^?1, large average pore diameter of 9.8 nm, high contents of doped heteroatoms (N, O and S), fairly high graphitization degree and dense defects, corresponding to dense active sites and excellent transportation of both mass and electrons. Therefore, the EW-650 shows higher activity than commercial Pt/C for ORR in both alkaline and acidic media even at higher mass loadings, with excellent cyclic stability. The effects of reaction temperature and electrolyte concentration on ORR activity are also studied. It is found that appropriate temperature and electrolyte concentration speed up ORR kinetics, ensure higher oxygen solubility and favor mass transportation.     

Stability of hemin/C electrocatalyst for oxygen reduction reaction

Hemin has been reported to be an effective electrocatalyst for mediating the oxygen reduction reaction. In this work, the stability of hemin/C is extensively investigated in both acid and alkaline media by the electrochemical methods. It is found that the pristine hemin/C yields significant change in the composition and the electrochemical features when it undergoes the potential cycling in acid media. In comparison, the catalyst shows superior stability in alkaline media. The pyrolysis can improve the stability of the hemin/C catalyst by removing the organic groups in hemin; however, the heat treatment cannot prevent the metal ion loss in acid media. Finally, the acid-leaching experiment reveals that the active center for the 4-electron reaction tends to get lost in acid, indicating that the iron metal ion should be involved in catalyzing the 4-electron reduction reaction. Furthermore, the XPS result indicates that the element N is also involved in the active center. Therefore, it can be concluded that the Fe–N contributes to the active center for the complete reduction of oxygen in alkaline media.     

Microbial synthesis of highly dispersed nano-Pd electrocatalyst for oxygen reduction reaction

Microbial fabrication is eco-friendly for nobel-metal catalysts typically used in proton exchange membrane fuel cell (PEMFC). In our study, nano-Pd electrocatalysts were successfully prepared by using three Shewanellas as precursors through hydrogen reduction (200 °C) and carbonization (800 °C). The analysis revealed that the catalysts showed outstanding ORR electrocatalytic performance via a predominant four-electron oxygen reduction pathway in alkaline medium. The best performance was obtained for Pd/HNC-32, which showed a mass activity at 0.526 A mg^?1, 3.78 times higher than that of commercial Pd/C. Shewanella putrefaciens CN-32 was a more effective Pd-adsorbent. The enhanced performance can be ascribed to the small Pd-particle size and uniform dispersion on microbial support, which results from stronger hydrophilicity of Shewanella putrefaciens CN-32. The content of nitrogen is another key to the performance of Pd/HNC-32. This study developed a promising strategy for screening microbial strains for electrocatalyst fabrication.     

Three-dimensional nitrogen-doped carbon nanotubes/carbon nanofragments complexes for efficient metal-free electrocatalyst towards oxygen reduction reaction

Heteroatom-doped carbon materials as one of the most promising oxygen reduction reaction (ORR) catalysts have attracted much attention. Rational design and exploration of suitable heteroatom-doped carbon materials greatly affects their ORR performance. Herein, we successfully prepared nitrogen-doped carbon nanotubes/carbon nanofragments (NCNT/CNF) complexes by a pyrolysis process using oxidized open-ended carbon nanotubes (OCNT)/oxidized carbon nanofragments (OCNF) hybrids as carbon precursors. The effect of carbon precursors on the synthesis of the corresponding nitrogen-doped carbon products was systematically investigated. The result showed the OCNT retained good conductivity, while the OCNF offered adequate structure defects for efficient post-doping. Benefiting from the co-merits of sole constitute, the obtained NCNT/CNF_1-15 (1–15 refers to the mass ratio) complexes possessed a typical three-dimensional architecture and much increased specific surface area, which facilitated reactant/electrolyte infiltration and ion/electron transfer. More importantly, they built the most optimized balance on ORR catalytic sites and conductivity. Thus, the NCNT/CNF_1-15 complexes showed much enhanced ORR performance. Clearly, our work provides a good guidance on the design of advanced heteroatom-doped carbon-based ORR catalysts.     

Hollow NH2-MIL-101@TA derived electrocatalyst for enhanced oxygen reduction reaction and oxygen evolution reaction

Non-precious metal-based electrocatalysts with excellent activity and stability are highly desired for the sluggish oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Herein, a tannic acid (TA) etching strategy is used to inhibit the metal aggregation and achieve muti-metal doping. The hollow NH₂-MIL-101@TA derived Fe–N–C catalyst exhibits superior ORR catalytic activity with an E_1/2 of 0.872 V and a maximum output power density of 123.4 mW cm⁻² in Zn-air battery. Since TA can easily chelate with metal ions, Fe/Co–N–C and Fe/Ni–N–C are also synthesized. Fe/Ni–N–C manifests exceptional bifunctional activity with an E_j = 10 of 1.67 V and a potential gap of 0.833 V between E_j = 10 and E_1/2 in alkaline electrolyte, which is 45 mV smaller than Pt/C–IrO₂. The improvement of ORR and OER performance of the catalysts via the simple TA etching and chelation method provides a novel strategy for the design and synthesis of efficient electrocatalysts.     

Pt nanodendrites anchored on bamboo-shaped carbon nanofiber arrays as highly efficient electrocatalyst for oxygen reduction reaction

In order to improve the Pt utilization and enhance their catalytic performance in fuel cells, a novel composite electrode composed of single-crystalline Pt nanodendrites and support constructed by bamboo-shaped carbon nanofiber arrays (CNFAs) on carbon paper, is reported. This electrode is designed by growing vertically CNFAs on carbon paper via plasma enhanced chemical vapor deposition, followed by the direct synthesis of Pt nanodendrites using a simple surfactant-free aqueous solution method. Electron microscopy studies reveal that the Pt nanodendrites are uniformly high dispersed and anchored on the surface of CNFAs. Electrochemical measurements demonstrate that the resultant electrode exhibits higher electrocatalytic activity and stability for oxygen reduction reaction than commercial Pt/C catalyst, suggesting its potential application in fuel cells.     

In-situ synthesis of Fe,N, S co-doped graphene-like nanosheets around carbon nanoparticles with dual-nitrogen-source as efficient electrocatalyst for oxygen reduction reaction

Iron, nitrogen, sulfur co-doped Fe/N/C catalyst (poly-AT/Me–Fe/N/C) with the structure of graphene-like nanosheets around carbon nanoparticles were successfully synthesized for oxygen reduction reaction (ORR). 2-Aminothiazole and melamine were utilized as the dual-nitrogen-source. The results showed that 2-Aminothiazole, as the nitrogen and sulfur source, contributed to in-situ synthesizing graphene-like nanosheets around KJ-600 carbon nanoparticles with high specific surface area (1098 m²/g). Proper method to introduce melamine during the synthesis could increase the content of pyridinic-N and Fe-N_x moieties in the catalyst without changing the morphology. Due to the high surface area and high content of pyridinic-N and Fe-N_x moieties, the obtained poly-AT/Me–Fe/N/C catalyst exhibited high electrochemical activity and stability with the half-wave potential of 0.84 V (RHE) in 0.1 M NaOH solution, which is merely 17 mV lower than commercial Pt/C. The electron transfer number was 3.83, indicating a nearly 4e^? transfer for the ORR with low HO₂^? yield.