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Efficient electrocatalyst of oxygen reduction reaction (ORR) is crucial for a variety of renewable energy applications and heteroatom-doped carbon materials have demonstrated promising catalytic performance towards ORR. In this paper we report a bioinspired method to synthesize nitrogen/sulfur (N/S) co-doped graphene as an efficient ORR electrocatalyst via self-polymerization of polydopamine (PDA) thin layer on graphene oxide sheets, followed by reacting with cysteine and finally thermal annealing in Argon (Ar) atmosphere. As-prepared N/S co-doped graphene exhibits significantly enhanced ORR catalytic activity in alkaline solution compared with pristine graphene or N-doped graphene. It also displays long-term operation stability and strong tolerance to methanol poison effect, indicating it a promising ORR electrocatalyst. [ABSTRACT FROM AUTHOR]

Two catalysts are synthesized by wet impregnation of multi walled carbon nanotubes (MWCNT) with a complex formed between Co(II) ions and the nitrogen-containing molecule 2,4,6-tris(2-pyridyl)-1,3,5-triazine (TPTZ), followed by one or two identical heat treatments in N 2 atmosphere at 800 °C for 3 h. Catalysts are fully characterized by FESEM, EDX, BET, XRD, FTIR, TGA, XPS analyses, and electrochemical techniques. The electrocatalytic activity towards oxygen reduction reaction (ORR) of the catalysts in acid conditions is assessed by means of a rotating disk electrode (RDE) apparatus and a specific type of cell equipped with a gas diffusion working electrode (GDE). In both testing approaches, the catalyst heat-treated twice (Co-N/MWCNT-2) exhibits higher electroactivity than the catalyst heat-treated once (Co-N/MWCNT-1). Chronoamperometries both in RDE and GDE cell are also performed, showing less electroactivity decay and better current performance for the catalyst heat-treated twice. [ABSTRACT FROM AUTHOR]

Synthesized by dripping iron acetate into the N-doped carbon film enriched with pyridinic N and followed by annealing at 800 °C, Fe–N-doped amorphous carbon (d Fe–N -C) with an Fe content of 0.2 at.% showed excellent electrocatalytic activity, stability and methanol tolerance via a four-electron pathway for oxygen reduction reaction (ORR), which outperformed commercial Pt/C catalyst. More importantly, by tuning the Fe content and annealing temperature, the trace Fe in d Fe–N -C was supposed to form high active FeN 4 sites with pyridinic N and played an important role in the excellent electrocatalytic performance for ORR. [ABSTRACT FROM AUTHOR]

Nitrogen-doped carbon nanofibers (NCNFs) are prepared by the thermal treatment of carbon nanofibers (CNFs) using urea as nitrogen source. Scanning electron microscopy, transmission electron microscopy and X-ray photoelectron spectroscopy have been employed to characterize the morphology and composition of CNFs and NCNFs. Compared with CNFs, NCNFs display thinner diameter, rougher surface and higher content of pyrrolic-N. As a metal-free catalyst for ORR, NCNFs exhibit comparable catalytic activity, significantly enhanced long-time stability and selectivity in comparison with commercial available Pt/C catalyst. Importantly, the self-supported NCNFs films could be conveniently utilized for electrode modification which is attractive in fuel cells. This work offers a promising metal-free catalyst as an alternative for Pt/C catalyst. [ABSTRACT FROM AUTHOR]

The successful commercialization of fuel cells requires the efficient electrocatalyst to make the oxygen reduction reaction (ORR) fast because of the sluggish nature of ORR and the high cost of the platinum catalysts. In this work, we report the excellent performance of metal-free nitrogen-doped porous carbon nanosheets (NPCN) with hierarchical porous structure and a high surface area of 1436.02 m 2 g −1 for catalyzing ORR. The active NPCN is synthesized via facile high-temperature carbonization of natural ginkgo leaves followed by purification and ammonia post-treatment without using additional supporting templates and activation processes. In O 2 -saturated 0.1 M KOH solution, the resultant NPCN exhibits a high kinetic-limiting current density of 13.57 mA cm −2 at −0.25 V (vs. Ag/AgCl) approaching that of the commercial Pt/C catalyst (14 mA cm −2 ) and long-term electrochemical stability. Notably, the NPCN shows a slightly negative ORR half-wave potential in comparison with Pt/C (Δ E 1/2 = 19 mV). The excellent electrocatalytic properties of NPCN originate from the combined effect of optimal nitrogen doping, high surface area, and porous architecture, which induce the high-density distribution of highly active and stable catalytic sites. [ABSTRACT FROM AUTHOR]

Currently, the development of nitrogen (N) doped carbon based non-precious metal ORR catalysts has become one of the most attractive topics in low temperature fuel cells. Here, we demonstrate a green synthesis route of N-self-doped carbon materials by using eggs as N sources combining with iron sources and multi-walled carbon nanotubes (CE–Fe–MWNT). After carbonized, such hybrid materials possess an outstanding electrocatalytic activity towards ORR comparable to the commercial Pt/C catalyst in alkaline media, and both superior stability and fuel (methanol and CO) tolerance than the commercial Pt/C catalyst, which provide a promising alternative to noble metal catalysts by using abundant natural biological resources. [ABSTRACT FROM AUTHOR]

Abstract: Hierarchical porous iron and nitrogen co-doped carbons (HP–Fe–N–Cs) as efficient cathode catalysts for oxygen reduction reaction (ORR) in neutral media are reported. The HP–Fe–N–Cs are prepared by using polypyrrole as nitrogen source and poly(vinyl alcohol) (PVA) hydrogel-based composites as in-situ templates. In studying the effect of the iron and the hierarchical porous structure on the nitrogen-doped carbon support for ORR, we find that HP–Fe–N–Cs show more positive onset potential, higher cathodic current density, and higher electron transfer number for the ORR in neutral media than iron-free hierarchical porous nitrogen-doped carbon (HP–N–C) and non-hierarchical porous iron and nitrogen co-doped carbon (Fe–N–C), highlighting the importance of the iron and the hierarchical porous structure for improving the ORR performance. Furthermore, HP–Fe–N–Cs show better durability than the commercial Pt/C catalysts in neutral media, and the microbial fuel cells (MFCs) equipped with HP–Fe–N–Cs catalysts on cathodes exhibit comparable power outputs with those of MFCs with commercial Pt/C cathode catalysts. [Copyright &y& Elsevier]

Highlights: [•] Ionic liquids are promising precursors for nitrogen-doped carbon catalyst for ORR. [•] Use of transition metal in the pyrolysis of IL is important for high ORR activity. [•] The graphitic-N content in the sp2-carbon network is key factor for high ORR. [•] Co is an effective metal compared to Ni for nitrogen-doped carbon catalyst. [Copyright &y& Elsevier]

Highlights: [•] Few-walled carbon nanotubes (FWCNTs) are synthesized by a CVD method. [•] N-FWCNTs are obtained by treatment with polyaniline and pyrolysis at high temperature. [•] N-FWCNTs with only ∼0.5at.% show high activity for oxygen reduction reaction (ORR). [•] ORR activity comparable to Pt-C is observed both in electrochemical cell and alkaline fuel cell. [Copyright &y& Elsevier]

[Display omitted] • Highly dispersed Co atoms anchored in porous N-doped carbon is synthesized. • The p –Co–N–C exhibits excellent activity and selectivity for H 2 O 2 electrosynthesis. • The p –Co–N–C shows promising application for the degradation of organic pollutants. Cobalt–nitrogen–carbon (Co–N–C) materials exhibit great potential for H 2 O 2 electrosynthesis through the oxygen reduction reaction (ORR). However, the encapsulated Co nanoparticles reduce the Faradic efficiency of H 2 O 2 production. Herein, highly dispersed cobalt atoms anchored in porous N-doped carbon (p –Co–N–C) via a carbonization-alkalization-acidification strategy are prepared and prove to be efficient for H 2 O 2 electrosynthesis in acidic media. The H 2 O 2 selectivity on the p –Co–N–C is over 90%, which is three times higher than that of Co nanoparticles encapsulated in N-doped carbon. Notably, the p –Co–N–C displays a H 2 O 2 production rate of 2,460.8 mg L−1h−1 and a malachite green degradation rate of 90% within 8 min when employed in a flow cell. The enhanced performance of p –Co–N–C for H 2 O 2 electrosynthesis originates from the highly dispersed Co–N x species and hierarchical porous architecture. The Co–N x species can provide active sites for O 2 and reaction intermediate adsorption and the hierarchical porous architecture can promote the diffusion of H 2 O 2 into the bulk solution. This work provides a facile synthesis strategy for non-precious metal materials in various energy-related applications. [ABSTRACT FROM AUTHOR]

[Display omitted] • Single-Cu-atoms and Cu clusters anchored nitrogen-doped porous carbon is developed. • As-prepared porous carbon shows ultra-high specific surface area of 3264 m2 g−1. • The catalysts exhibit the pH-universal electrocatalytic activity for oxygen reduction reaction. • The catalytic activity in acidic medium outperforms all of reported Cu-based catalysts. • The enhanced activity can be attributed to the synergistic effects of single-Cu-atom and Cu cluster. Oxygen reduction reaction (ORR) plays a significant role in many renewable energy storage and conversion devices. Various kinds of transition metal-based electrocatalysts were developed to promote the ORR. Among them, Cu-based catalysts were rarely studied due to their intrinsic de-active feature in bulk state, especially in acidic medium. In this work, single Cu atoms and Cu clusters-anchored nitrogen-doped porous carbons are rationally developed. As electrocatalysts for ORR, half-wave potential (E 1/2) of 0.88 V and diffusion limiting current density (J L) of 5.88 mA cm−2 can be achieved in 0.1 M KOH, exceeding the most of reported non-precious catalysts and commercial Pt/C. Significantly, as-prepared catalysts exhibit the state-of-the-art performance in acidic medium among all of reported Cu-based catalysts with the E 1/2 of 0.80 V and J L of 5.86 mA cm−2. Theoretical calculations indicate that the nitrogen-coordinated Cu atoms are the dominating active sites, and the neighboring Cu cluster increases the electron density of d orbitals of single-Cu-atom, which weakened the O-O interaction, thus further boost ORR performance. This work not only presents a facile strategy to fabricate efficient catalysts but also identifies the great potential of Cu based materials for ORR in both alkaline and acidic media. [ABSTRACT FROM AUTHOR]

[Display omitted] • Influence of Fe bonded with different type N on the stability of ORR was analyzed. • Fe-N-C catalyst with high pyridinic N content was successfully prepared. • Fe-N-C with high pyridinic N content presents much enhanced ORR stability. • The practical value of catalyst was tested in PEMFC and Zn-air cell. Developing advanced non-precious metal catalysts towards acidic oxygen reduction reaction (ORR) is critical for electrochemical energy conversion devices. Fe-N-C catalysts are demonstrated to be the most promising alternatives to platinum-based catalysts for ORR. Herein, Fe single atoms (SAs) coordinated by pyridinic nitrogen catalysts (denoted as Fe-pyridinic N-C) are synthesized through pyrolysis of ZIF-8 encapsulating ferrocene. Owing to the synergistic effects between Fe SAs and pyridinic N, Fe-pyridinic N-C exhibits remarkable ORR activity and outstanding stability in acid media, evidenced by golden kinetic current density of 9.71 mA cm−2 at 0.8 V, along with only 21 mV decrease in half-wave potential after 20,000 cycles. Theoretical calculations demonstrate that pyridine-type N possesses stronger binding energy with Fe SAs compared with pyrrole-type N, in other words, high pyridinic N content will help stabilize the catalyst. This study will be of great significance for the development of non-noble metal catalysts towards ORR with enhanced stability in acidic media. [ABSTRACT FROM AUTHOR]

Via a simple microwave-assistance without template and metal ligand, nitrogen doped porous carbon polyhedrals supported Fe and Ni dual single-atomic catalysts (FeNi-DACs-PNCH) were sucessfully prepared, and exhibited superb ORR performances with positive E 1/2 (0.89 V vs RHE), excellent durability and strong tolerance to methanol and SCN- in alkaline media. Moreover, with FeNi-DSAs-PNCH as the air cathode and zinc foil as the anode, an assembled Zn-air battery exhibits a higher open-circuit voltage of 1.48 V and a larger specific capacity of 802.18 mAh g−1 than that of the Pt/C-based Zn-air battery (1.37 V and 664.78 mAh g−1, respectively). [Display omitted] • Dual single-atomic catalysts prepared via microwave-aid with no template and metal ligand. • The catalysts have porous structure, large surface area and abundant active sites. • The catalysts showed high ORR activity superior to the commercial Pt/C. • The proposed Zn-air battery exhibits a promising practical application prospect. • DFT calculation verified the d-band center modulating for boosted ORR catalysis. Constructing dual-metal single-atom catalysts (DSAs) now stands for a unique and worthwhile strategy for developing high-efficiency electrocatalysts for oxygen reduction reaction (ORR). However, the facile synthesis of DSAs uniformly located on nitrogen porous carbon materials is still challenging. Herein, Fe and Ni dual-metal single-atomic active sites uniformly located on nitrogen doped porous carbon polyhedrals (FeNi-DSAs-PNCH) are successfully prepared by a facile and rapid microwave-assisted adsorption and subsequent pyrolysis process with free template and free metal ligand. The FeNi-DSAs-PNCH catalyst exhibits boosted ORR activity and long time stability. Experimental investigations and density functional theory calculation results verify that, besides the hierarchical porous structure, large specific surface area and abundant catalytic active sites, the adjacent Ni-Nx atomic sites can modulate the d-band center of Fe-Nx single atomic active centers and balance the adsorption–desorption affinities to O 2 molecules and oxygen-containing intermediates on Fe-Nx, thus leading to an superior ORR activity with a more positive half-wave potential (0.89 V vs. RHE) than the single Fe or Ni atomic catalyst and the commercial Pt/C catalyst. Moreover, with FeNi-DSAs-PNCH as the air cathode and zinc foil as the anode, an assembled Zn-air battery exhibits a higher open-circuit voltage of 1.48 V and a larger specific capacity of 802.18 mAh g−1 than that of the Pt/C-based Zn-air battery (1.37 V and 664.78 mAh g−1, respectively). This work develops a convenient strategy for preparing dual-metal single-atomic cataysts as promising substitutes for the commercial Pt/C catalysts in the practical energy conversion applications, and also offers experimental and theoretical guidance for rational designing and improvement of ORR and other catalysts by tailoring the d-band center of the active sites. [ABSTRACT FROM AUTHOR]

Abstract: Melamine-derived N-doped mesoporous carbon (MNMC) is synthesized by the pyrolysis of lysine and melamineunder at nitrogen atmosphere using ferric chloride as a dopant and SiO2 nanoparticles as hard templates to form mesoporous architecture. The N content in the bulk of carbon materials is as high as 11.3% and ca. 40.6% of N is in the form of pyridinic-N. The surface area of MNMC is ca. 650 m2 g−1 with a pore size distribution in the range of 2.2–34.5 nm. Compared to commercial Pt/C (20 wt%), MNMC exhibits much better electrocatalytic activity, better durability, and higher methanol tolerance for oxygen reduction reaction (ORR) in alkaline medium. Particularly, the onset ORR potential and half-wave ORR potential of MNMC are 1.059 and 0.871 V vs. RHE respectively, which are higher than those of commercial Pt/C. [Copyright &y& Elsevier]

A cost-effective chemical, N,N′-bis(salicylidene)ethylenediamine (salen), is used as a ligand to form a carbon-supported Co-salen complex (Co-salen/C) by a simple solid-sate reaction. The Co-salen/C is then pyrolyzed at 600, 700, 800, 900, and 1000 °C to form carbon-supported Co–N–S/C catalysts for the oxygen reduction reaction (ORR). XRD, EDX, TEM, and XPS are used to characterize the catalysts' composition, crystalline nature, morphology, and possible surface groups induced by heat-treatment. Investigation of the catalytic activity and the ORR mechanisms using rotating disk electrode and rotating ring-disk electrode techniques demonstrates that all of these Co–N–S/C catalysts are highly active for the ORR in an O2-saturated 0.1 M KOH solution, but the catalyst heat treated at 700 °C gives the best ORR activity. The overall electron transfer number for the catalyzed ORR was determined to be 3.6–3.9, with 3.7–19.9% H2O2 production over the potential range of −0.05 to −0.60 V, suggesting that the ORR catalyzed by Co–N–S/C catalysts is dominated by a 4-electron transfer pathway from O2 to H2O. In addition, these catalysts exhibit superior methanol tolerance to commercial 40% Pt/C catalyst, thus the Co–N–S/C catalysts are promising for use as electrocatalysts in alkaline polymer electrolyte membrane fuel cells. [ABSTRACT FROM AUTHOR]

Highlights: [•] There was a linear relation between the binding energy of OOH* and OH* for the N-GNRs. [•] The most OER and ORR active sites were identified near the edge but not exactly on the edge of the armchair nanoribbons. [•] The minimum theoretic OER and ORR overpotential was calculated. [•] The calculations suggested that N-GNRs were a highly promising OER/ORR catalyst. [ABSTRACT FROM AUTHOR]

Highlights: [•] We propose an alternative method for doping nitrogen in carbon materials. [•] Nitrogen is successfully doped in carbon black and ketjen black confirmed with Raman and XPS. [•] Nitrogen doped carbons exhibit better electrocatalytic activity with high mass activity. [•] Nitrogen doped KB shows better physical and electrocatalytic characteristics of all samples. [Copyright &y& Elsevier]

Abstract: Nitrogen doped holey graphene (NHG), with in-plane holes in its sheet plate, has been synthesized in this work through the potassium hydroxide (KOH) etching and ball milling of nitrogen doped graphene (NG). It shows that the KOH etching and ball milling does not distinctly alter the elemental composition and the relative percentages of functional groups in NG, but produce holes in its in-plane sheet plate. The obtained NHG can then be used as an active electrode material for supercapacitors and as an active electrocatalyst for oxygen reduction reaction, and exhibits significantly higher electrochemical performance than the corresponding NG. Its improved electrochemical performance could be attributed to its specific holey structure in the sheet plate and porous structure in its randomly stacked solid, which provide it with more active edge atoms, better accessibility to electrolyte, larger accommodation space for ions, faster electrolyte diffusion and movement and so on. [Copyright &y& Elsevier]

Abstract: A highly active electrocatalyst for oxygen reduction reaction, manganese modified glycine derivative-carbon (Mn-CN x ), is synthesized by a two-step carbonizing process. X-ray diffraction, Raman spectroscopy, and X-ray photoelectron spectroscopy are used to characterize structure and morphology of the catalysts. Electrochemical tests show that Mn-CN x has higher catalytic activity for oxygen reduction reaction than CN x derived glycine and Mn modified Vulcan carbon. Moreover, the half-wave potential of Mn-CN x is only 12 mV lower than that of commercial Pt/C. Mn-CN x also has excellent durability to methanol crossover in alkaline solution, and thus provides a promising low cost, non-precious metal cathode catalyst for fuel cells. [Copyright &y& Elsevier]

Abstract: Transition metal is usually required for obtaining N-doped carbon (dN-C) catalysts toward oxygen reduction reaction, leading to an intense debate on whether the active sites in dN-C correlate to transition metal. Here, we report that metal-free amorphous dN-C was synthesized using simple one-step magnetron sputtering at relatively low temperature. The chemical bonding states of N atoms, which play a key role in optimizing the electrocatalytic activity, can be tuned by adjusting deposition temperature. The metal-free dN-C with high pyridinic N content exhibits high electrocatalytic activity, and its stability and methanol tolerance are much better than commercial Pt/C catalyst. [Copyright &y& Elsevier]

Abstract: Well defined nitrogen-doped graphene (NG) is prepared by a transfer doping approach, in which the graphene oxide (GO) is deoxidized and nitrogen doped by the vaporized polyaniline, and the GO is prepared by a thermal expansion method from graphite oxide. The content of doped nitrogen in the doped graphene is high up to 6.25 at% by the results of elements analysis, and oxygen content is lowered to 5.17 at%. As a non-precious metal cathode electrocatalyst, the NG catalyst exhibits excellent activity toward the oxygen reduction reaction, as well as excellent tolerance toward methanol. In 0.1 M KOH solution, its onset potential, half-wave potential and limiting current density for the oxygen reduction reaction reach 0.98 V (vs. RHE), 0.87 V (vs. RHE) and 5.38 mA cm−2, respectively, which are comparable to those of commercial 20 wt% Pt/C catalyst. The well defined graphene structure of the catalyst is revealed clearly by HRTEM and Raman spectra. It is suggested that the nitrogen-doping and large surface area of the NG sheets give the main contribution to the high ORR catalytic activity. [Copyright &y& Elsevier]

Abstract: Nitrogen-doped hollow mesoporous carbon spheres has been synthesized from mesoporous silica spheres using glycine as carbon and nitrogen precursor. The wall of the spheres is composed by broken graphene. The metal free nitrogen-doped hollow mesoporous carbon spheres are proven to be active electrocatalyst for the oxygen reduction reaction in alkaline solution. A unique advantage of the nitrogen-doped hollow mesoporous carbon sphere is its methanol-tolerant property because of the absence of active metal. The catalytic activity is ascribed to the pyridinic-nitrogen formed during pyrolysis and the graphene-like structure. To the best of our knowledge this is the first report on the nitrogen-doped hollow mesoporous carbon sphere as a metal-free electrocatalyst for the oxygen reduction reaction which is an important reaction in fuel cell. The prepared mesoporous carbon material can also be used as catalyst support and find application both in the anode and cathode of fuel cell. [Copyright &y& Elsevier]

Nitrogen (N)-doped carbons reportedly exhibit good electrocatalytic activity for the oxygen reduction reaction (ORR) of fuel cells. This work provides theoretical insights into the ORR mechanism of N-doped graphene by using density functional theory calculations. All possible reaction pathways were investigated, and the transition state of each elementary step was identified. The results showed that OOH reduction was easier than O–OH breaking. OOH reduction followed a direct Eley–Rideal mechanism (the OOH species was in gas phase, but H was chemisorbed on the surface) with a significantly low reaction barrier of 0.09 eV. Pathways for both four-electron and two-electron reductions were possible. The rate-determining step of the two-electron pathway was the reduction of O 2 (formation of OOH), whereas that of the four-electron pathway was the reduction of OH into H 2O. After comparing the barriers of the rate-determining steps of the two pathways, we found that the two-electron pathway was more energetically favored than the four-electron pathway. [ABSTRACT FROM AUTHOR]

Abstract: Spillover, a well-known phenomenon in heterogeneous catalysis referring to the transport of the adsorbed intermediates over the catalyst/support interface, could enhance the catalytic performance by providing additional active sites. Here, we report the spillover-promoted electrocatalytic activity of Pt supported on nitrogen-doped carbon black (NCB) for the oxygen reduction reaction (ORR). By treating Vulcan XC-72R carbon black (CB) at 600 °C under gaseous NH3, NCB of near 1 at% surface nitrogen content is obtained. The catalyst of Pt supported on NCB (Pt/NCB) exhibits simultaneously smaller particle sizes and higher electrochemical surface area and electrocatalytic activity for the ORR than the catalyst of Pt supported on pristine CB (Pt/CB) prepared with the same impregnation method. Particularly, the activity enhancement of Pt/NCB over Pt/CB surpasses that expected due to the surface area increase, which seems to conflict with the common belief that Pt nanoparticles of smaller sizes would have lower area specific activities for the ORR. Cyclic voltammetric responses of these catalysts implied that the oxygenated adsorbates formed on Pt can transport to surface of the NCB support, which may be responsible for the increased area specific activity of the Pt/NCB catalyst. [Copyright &y& Elsevier]

• Co/Co 9 S 8 nanoparticles decorated N, S dual-doped carbon leaves was prepared via DTO molecule coating leaf-shaped ZIFs. • The functionality of DTO simultaneously optimizes 2D nanostructure and component (S doping) by the confinement effect. • The Co/Co 9 S 8 -NCL-30 exhibits excellent ORR performance, stability and zinc-air battery performance. [Display omitted] Substituting costly Pt-based oxygen reduction reaction (ORR) catalysts with highly active and stable non-precious metal catalysts is a great challenge in zinc-air batteries. Herein, we fabricated Co/Co 9 S 8 nanoparticles decorated nitrogen, sulfur dual-doped carbon leaves (Co/Co 9 S 8 -NCL) with outstanding ORR performance by pyrolysis of dithiooxamide (DTO) molecule modified two-dimensional (2D) leaf-shaped zeolitic imidazolate framework (ZIF-L). The functionality of DTO simultaneously optimizes 2D nanostructure and component (S doping) by the confinement effect due to the coordination interaction between S atoms of DTO and Co2+ in ZIF-L. Benefiting from the synergistic effect between Co-N x sites and Co/Co 9 S 8 species coupled with unique two-dimensional N, S-codoped carbon leaves, the resulting Co/Co 9 S 8 -NCL-30 exhibits a remarkable ORR activity with a half-wave potential of 0.852 V comparable to Pt/C (0.843 V) and outstanding long-term stability. Impressively, the Zn-air battery with Co/Co 9 S 8 -NCL-30 achieves high power density of 112 mW cm−2 and specific capacity of 799 mAh g−1 Zn. This work will present a new pathway to prepare highly active and durable 2D transition metal-based carbon nanomaterials in zinc-air batteries. [ABSTRACT FROM AUTHOR]

[Display omitted] • Melamine was added to intrigue the self-assembly of Cu/Zn MOF nanosheet. • In situ trapped N-rich molecules benefit the formation of pores and Cu-N 4 sites. • Cu-SAs/NSs display remarkable ORR activity and excellent stability. • Cu-SAs/NSs exhibit superb performance when used in rechargeable Zn–air battery. • The strategy can be extended to prepare other metal-based single atoms. The development of noble-metal-free single atom electrocatalysts (SAECs) with both remarkable activity and durability for oxygen reduction reaction (ORR) are in great demand for large-scale commercialization of proton-exchange membrane fuel cells and metal-air batteries. Here, we developed a novel strategy to fabricate high-performance Cu-SAs/NSs from pyrolysis of two-dimensional (2D) Cu/Zn bimetallic MOF. Specifically, nitrogen-rich molecules (melamine) were deliberately added to intrigue the self-assembly of Cu/Zn bimetallic MOF, and contribute to the formation of highly porous structure and abundant Cu-N 4 active sites. With the enhanced accessibility of active sites and mass transport, the as-developed Cu-SAs/NSs display a remarkable ORR performance in alkaline media, outperforming the benchmark Pt/C and most of platinum group metals (PGMs)-free electrocatalysts reported to date. Notably, this facile strategy can be extended to fabricate other transition metal (TM, TM = Fe, Co, Ni)-based single atoms. This work presents a novel and general strategy to construct carbon-based SAECs towards ORR. [ABSTRACT FROM AUTHOR]

[Display omitted] • Cu 0.6 -N-CNFs were prepared using SCC as an organometallic copper source. • The Cu-N 4 chelating structure in SCC was retained in the Cu 0.6 -N-CNFs. • The Cu 0.6 -N-CNFs exhibited ORR activity similar to that of commercial Pt/C catalysts. Single-atom catalysts (SACs) have attracted much attention in the field of oxygen reduction reactions (ORR) as a result of their high selectivity and effective atom utilization. Cu SACs are particularly difficult to prepare since copper is prone to agglomeration, which leads to the formation of metal particles. In this study, using sodium copper chlorophyllin (SCC) as an organometallic copper source, carbon nanofibers incorporating Cu-N 4 structures were prepared using electrospinning technology. This new type of Cu SAC has a huge surface area (1005.615 m2·g) and a 3D network structure, which are conducive to the exposure of more active sites as well as to electron conduction and material transport. Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy revealed that the Cu-N 4 structure was preserved in the electrocatalyst, and was responsible for the catalytic activity towards the ORR. The Cu–N-CNFs exhibited higher catalytic activity and greater stability than commercial Pt/C in an alkaline medium, suggesting the possibility of using Cu SACs to replace commercial Pt/C electrocatalysts. [ABSTRACT FROM AUTHOR]

[Display omitted] • A surface functional group regulation strategy was proposed for H 2 O 2 production. • The optimized CoNCF-HNO 3 exhibits satisfactory 2e− ORR selectivity in acid medium. • Positive correlation between C-O-C content and 2e− ORR selectivity was disclosed. • A sterilization system for water disinfection was developed based on CoNCF-HNO 3. Electrochemical synthesis has emerged as a promising alternative method for industrial production of hydrogen peroxide (H 2 O 2). Although transition metal-nitrogen-carbon moieties have been regarded as efficient catalysts for oxygen reduction reaction (ORR), they are generally established for four-electron (4e−) pathway, rather than two-electron (2e−) one for selective generation of H 2 O 2. Herein, we propose a strategy to achieve cobalt-carbon hybrids with high 2e− selectivity for H 2 O 2 production in acidic media via tailoring their surface structure and coordination environment. The correlation between 2e− ORR selectivity of the fabricated monolithic electrodes, i.e. Co nanoparticles embedded in N-doped oxo carbon framework (CoNCF), and their oxygen-containing functional groups is revealed. In particular, an excellent H 2 O 2 selectivity over 91 % in 0.05 M H 2 SO 4 is achieved, which exceeds most of previously reported 2e− ORR electrocatalysts. Moreover, a sterilization system for water disinfection is constructed, demonstrating potential practical applications. The smart design of multi-active sites and porous monolithic architecture opens a new avenue for preparing advanced electrode for H 2 O 2 generation and other environment/energy-related systems. [ABSTRACT FROM AUTHOR]

The high-quality hollow N-doping carbon nanoflowers (h-N-CFs) with nanosheets subunits are synthesized by using 2,5-diaminobenzoic acid-1,3,5-benzenetricarboxaldehyde (DABA-BTCO) complex nanoflowers as the self-template and nitrogen resource. The as-prepared h-N-CFs at 800 ℃ has excellent electrocatalytic oxygen reduction activity in both alkaline and neutral electrolytes, good long-term stability and eminent methanol tolerance, which is equal or even better than Pt/C electrocatalyst. [Display omitted] • Hollow N-doping carbon nanoflowers (h-N-CFs-800) are successfully prepared. • Covalent complexes act as calcination precursors and activated nitrogen sources. • Hollow and porous structure of h-N-CFs-800 increase the number of active sites. • The high ORR activity due to the unique hollow structure and abundant N doping. • h-N-CFs-800 has excellent ORR activity in both alkaline and neutral electrolytes. The synthesis of economic carbon-based metal-free catalysts with high electroactivity for the oxygen reduction reaction (ORR) is still a huge challenge for energy storage and conversion devices. Herein, the hollow N-doped carbon nanoflowers (h-N-CFs) with nanosheets subunits were synthesized by using 3,5-diaminobenzoic acid-1,3,5-benzenetricarboxaldehyde (DABA-BTCO) complex nanoflowers as the self-template and nitrogen resource. Various physical characterizations show that h-N-CFs with hollow and porous architecture have a high surface area (1390.3 m2g−1) and abundant activated N atoms (i.e., graphitic N and pyridinic N). Electrochemical measurements demonstrate that h-N-CFs synthesized at 800 °C can be used as an efficient metal-free ORR catalyst with prominent electroactivity and stability due to hollow architecture, abundant pores, and high N-doping content. Meanwhile, h-N-CFs also show eminent ORR selectivity (i.e., methanol tolerance) in alkaline media, which markedly surpasses benchmark Pt/C catalyst in the presence of methanol. [ABSTRACT FROM AUTHOR]

A simple method for the mechanochemical synthesis of an effective metal-free electrocatalyst for the oxygen reduction reaction was demonstrated. A nitrogen-doped carbon material was obtained by grinding a mixture of graphene oxide and melamine in a planetary ball mill. The resulting material was characterized by XPS, EPR, and Raman and IR spectroscopy. The nitrogen concentration on the N-bmGO surface was 5.5 at.%. The nitrogen-enriched graphene material (NbmGO has half-wave potential of −0.175/−0.09 V and was shown to possess high activity as an electrocatalyst for oxygen reduction reaction. The electrocatalytic activity of NbmGO can be associated with a high concentration of active sites for the adsorption of oxygen molecules on its surface. The high current retention (93% for 12 h) after continuous polarization demonstrates the excellent long-term stability of NbmGO. [ABSTRACT FROM AUTHOR]

Electrocatalyst is the pivotal component promoting the kinetics of oxygen reduction reaction in aqueous metal-air batteries. However, the content of increased bond as the active species is usually limited by the metal loading, tiny pore canal, insufficient nitrogen further restraining the electrocatalytic effectiveness of single-atom catalysts in oxygen reduction reaction (ORR). Herein, Co, N-dual doped carbon (Co/NNC) is prepared by a versatile strategy of the combination approach of SiO 2 template with extra nitrogen source. Based on ZIF-67 prepared with the assistance of SiO 2 template, the extra nitrogen source was introduced in the high-temperature pyrolysis procedure. The material characterizations of XRD, SEM, HRTEM, BET, Raman and XPS are conducted to synthetically analyze the functional role of extra nitrogen source. Moreover, the Co/NNC with increased Co-N x active sites is employed into two aqueous metal-air batteries of Zn-air and Mg-air batteries, which exhibits excellent performances especially in the aspects of discharge specific capacity, discharge stability and power density. [Display omitted] 1 SiO 2 template and extra nitrogen source are combined to prepare Co/NNC. 2 Extra nitrogen source boosts the Co-N x content of Co/NNC derived from ZIF-67. 3 In aqueous metal-air batteries, Co/NNC shows superior capacity performance than Pt/C. [ABSTRACT FROM AUTHOR]

In this study, we report on the facile synthesis of a novel electrocatalysts for the oxygen reduction reaction (ORR), based on reduced graphene oxide (RGO), functionalized with metallic and non-metallic elements. In particular, thanks to a fast one-pot microwave-assisted procedure, we induced, in the RGO graphene lattice, a combined doping with nitrogen and sulphur, and the simultaneous decoration with antimony oxide nanocrystals. The multi-doped–decorated material shows enhanced catalytic performance towards ORR, with respect to common nitrogen- or sulphur-doped carbon-based materials. The presence of co-doping is confirmed by transmission electron microscopy and X-ray photoelectron spectroscopy analysis. The detailed electrochemical characterization shows the simultaneous effects of dopant atoms on the catalytic behavior. In particular, the importance of nitrogen and sulphur atoms in driving the oxygen absorption, together with the role of antimony in enhancing the electrochemical performance toward the ORR, are discussed. [ABSTRACT FROM AUTHOR]

Abstract: Pt nanoparticles supported on nitrogen-doped porous carbon microspheres (Pt/CN) were synthesized via an in-situ spray-drying technique followed by calcination. The addition of ammonium hydroxide had a remarkable influence on the solution chemistry, which promoted the simultaneous formation of metallic Pt and nitrogen doping onto carbon support material. Furthermore, the precursor pH influenced the subsequent oxygen reduction activity of the product. Ultrahigh oxygen reduction reaction (ORR) activity was recorded for a catalyst prepared at a precursor pH of 8.4 with mass activity and specific activity were 564 mA mg−1 Pt and 834 μA cm−2 Pt, respectively. This investigation resulted in an effective strategy to escalate the catalyst ORR during limited catalyst surface area enhancement. [Copyright &y& Elsevier]

Abstract: Nitrogen-doped graphene (NG) materials have been prepared by hydrothermal reaction of graphite oxide (GO) with urea, and their electrocatalytic properties towards oxygen reduction reaction in 0.1 M KOH are investigated. The introduction of urea leads to successful nitrogen insertion in the form of pyridinic, pyrrolic, and graphitic bonding configurations with enhanced reduction of GO, and an increase in the mass ratio between urea and GO gives higher nitrogen contents, which is accompanied by more defects in microstructure. Reduction of O2 to OH− at lower overpotentials is favored by the incorporation of nitrogen, and the activity of NG is closely associated with nitrogen contents and microstructure. NG materials with ca. 7% nitrogen contents and moderate defect densities prepared from mass ratios of 1:200 and 1:300 (GO/urea) show the best performance. [Copyright &y& Elsevier]

Nitrogen-doped carbon (CN x) nanotubes were synthesized by thermal decomposition of ferrocene/ethylenediamine mixture at 600-900 °C. The effect of the temperature on the growth and structure of CN x nanotubes was studied by transmission electron microscopy, X-ray photoelectron spectroscopy, and Raman spectroscopy. With increasing growth temperature, the total nitrogen content of CN x nanotubes was decreased from 8.93 to 6.01 at.%. The N configurations were changed from pyrrolic-N to quaternary-N when increasing the temperature. Examination of the catalytic activities of the nanotubes for oxygen reduction reaction by rotating disk electrode measurements and single-cell tests shows that the onset potential for oxygen reduction in 0.5 M HSO of the most effective catalyst (CN x nanotubes synthesized at 900 °C) was 0.83 V versus the normal hydrogen electrode. A current density of 0.07 A cm at 0.6 V was obtained in an H/O proton-exchange membrane fuel cell at a cathode catalyst loading of 2 mg cm. [ABSTRACT FROM AUTHOR]

Abstract: Pt nanoparticles supported on nitrogen-doped reduced graphene oxide (NRGO) were investigated for use as proton exchange membrane fuel cell catalysts. Artfully, NRGO was synthesized using a lyophilisation-assisted N-doping method, and simultaneous reduction of graphene oxide (GO) was achieved. A nitrogen content as high as 5.06% was obtained with pyridinic-N as the dominant nitrogen species. Pt nanoparticles with an average diameter of 2.5nm were uniformly loaded on NRGO using impregnation methods. Both cyclic voltammetry and oxygen reduction reaction (ORR) measurements revealed a higher catalytic activity and lower losses of the electrochemically active surface area of this novel Pt/NRGO catalyst in comparison to those of the Pt/GO and conventional Pt/C catalysts. Significantly, the catalytic activity of the Pt/NRGO in ORR showed almost no degradation even after 1000 potential cycles, indicating that our new catalysts have excellent stability. A mechanism for improving the ORR activity and the stability of the Pt/NRGO was tentatively proposed and discussed. [Copyright &y& Elsevier]

It is of great significance in exploring alternative catalysts to platinum (Pt)-based materials for oxygen reduction reaction (ORR), because this reaction is invariably involved in various fuel cells and metal-air batteries. We herein reported the nitrogen doped graphene nanosheets (NGNSs) with pore volume of as high as 3.42 m/g and investigated their potential application as ORR catalysts, it was demonstrated the NGNSs featured high activity, improved kinetics and excellent long-term stability for ORR. The NGNSs were successfully used as cathode catalysts of microbial fuel cells (MFCs) and performed even better than the commercial Pt/C (Pt 10%) catalysts at the maximum power output. [ABSTRACT FROM AUTHOR]

Abstract: The aligned nitrogen-doped carbon nanotubes (NCNT) with bamboo-like structure are synthesized via thermal chemical vapor deposition using melamine and urea as different nitrogen precursors. Meanwhile, ferrocene is used as catalyst and carbon precursor. The resulting NCNT with melamine (M-NCNT) have shown superior ORR performance in terms of limiting current density and number of electrons transferred. Further characterizations by X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy illustrated higher nitrogen content and more defects in M-NCNT compared to that in NCNT with urea (U-NCNT), which indicate the important role of the nitrogen precursor in nitrogen content and structure of NCNT. It is concluded that higher nitrogen content and more defects of NCNT lead to high performance of ORR. [Copyright &y& Elsevier]

Abstract: In this work, iron- and nitrogen-functionalized graphene (Fe–N–G) as a non-precious metal catalyst is synthesized via a facile method of thermal treatment of a mixture of Fe salt, graphitic carbon nitride (g-C3N4) and chemically reduced graphene. The electrocatalytic activity of the prepared catalysts toward oxygen reduction reaction (ORR) evaluated by using linear sweep voltammetry tests shows that the Fe–N–G catalyst has more positive onset potential and increased reduction current densities as compared to the pristine graphene (P–G) catalyst, indicating an enhanced ORR activity of the Fe–N–G catalyst. More importantly, the Fe–N–G-MFC achieves the highest power density of 1149.8mWm−2, which is ∼2.1 times of that generated with the Pt/C-MFC (561.1mWm−2) and much higher than that of the P–G-MFC (109mWm−2). These results demonstrate that the Fe–N–G catalyst can hold the promise of being an excellent alternative to the costly Pt catalyst for practical MFC applications. [Copyright &y& Elsevier]

Abstract: The development of non-noble metal catalysts is of great interest due to their significant potential application in both fuel cell systems and metal–air batteries, particularly when considering long term commercial deployment. In this regard, novel Co-N-S/C non-noble metal catalysts supported on carbon, are synthesized in this study using a solvent-milling method followed by heat-treatment at elevated temperatures. Pyridine is used as the nitrogen-rich ligand for Co-N x precursor complex formation. The morphology and composition of the catalyst are characterized by X-ray diffraction (XRD), energy-dispersive X-ray (EDX) spectroscopy, transmission electron microscopy (TEM) as well as X-ray photoelectron spectroscopy (XPS). Several catalysts containing different amounts of Co are also synthesized. The optimal Co content is found to be in the range of 10–15wt% nominal, in terms of catalytic oxygen reduction reaction (ORR) activity. This catalyst shows high electroactivity for the ORR with a high stability in alkaline media. Using rotating disk electrode measurements, and Koutechy–Levich analysis, the overall electron transfer number in the catalyzed ORR is found to be 3.8–4.0, suggesting the catalyzed ORR is a four-electron transfer process from O2 to H2O. [Copyright &y& Elsevier]

Abstract: This study examines the role of transition metals (Co or Fe) on nitrogen-modified carbon-based catalysts for the oxygen reduction reaction (ORR). The nitrogen-modified carbon-based catalysts are synthesized by the pyrolysis process in the presence of polypyrrole (PPy) and ethylenediamine (ED) with different amounts of transition metals. Electrochemical data and inductively coupled plasma-atomic emission spectroscopy (ICP-AES) analysis do not support that the transition metal itself behaves as an active site for ORR. The X-ray photoelectron spectroscopy (XPS) and elemental analysis results show that the total nitrogen content and the active nitrogen functional groups, such as pyridinic-N and graphitic-N, are strongly dependent on the type of transition metal and the amount of transition metal used. Therefore, it is believed that transition metals serve to catalyze the formation of active nitrogen functional groups for the ORR by doping nitrogen into carbon. [Copyright &y& Elsevier]