Replacing precious platinum with earth-abundant materials for the oxygen reduction reaction (ORR) in fuel cells has been the objective worldwide for several decades. In the last ten years, the fastestgrowing branch in this area has been carbon-based metal-free ORR electrocatalysts. Great progress has been made in promoting the performance and understanding the underlying fundamentals.Here, a comprehensive review of this field is presented by emphasizing the emerging issues including the predictive design and controllable construction of porous structures and doping configurations, mechanistic understanding from the model catalysts, integrated experimental and theoretical studies, and performance evaluation in full cells. Centering on these topics, the most upto-date results are presented, along with remarks and perspectives for the future development of carbon-based metal-free ORR electrocatalysts.

While the carbon-based metal-free electrocatalysts for oxygen reduction reaction (ORR) have experienced great progress in recent years, the fundamental issue on the origin of ORR activity is yet far from being clarified. To date, the ORR activities of these electrocatalysts are usually attributed to different dopants, while the contribution of intrinsic carbon defects has been little touched. Herein, we report the high ORR activity of the defective carbon nanocages, which is better than that of the B-doped carbon nanotubes and comparable to that of the N-doped carbon nanostructures. Density functional theory (DFT) calculations indicate that pentagon and zigzag edge defects are responsible for the high ORR activity. The mutually corroborated experimental and theoretical results reveal the significant contribution of the intrinsic carbon defects to ORR activity, which is crucial for understanding the ORR origin and exploring the advanced carbon-based metal-free electrocatalysts.

Proton exchange membrane fuel cells are promising candidates for a clean and efficient energy conversion in the future, the development of carbon based inexpensive non-precious metal ORR catalyst has becoming one of the most attractive topics in fuel cell field. Herein we report a Fe- and N- doped carbon catalyst Fe-PANI/C-Mela with graphene structure and the surface area up to 702 m2 g−1. In 0.1 M HClO4 electrolyte, the ORR onset potential for the catalyst is high up to 0.98 V, and the half-wave potential is only 60 mV less than that of the Pt/C catalyst (Loadings: 51 μg Pt cm−2). The catalyst shows high stability after 10,000 cyclic voltammetry cycles. A membrane electrode assembly made with the catalyst as a cathode is tested in a H2-air single cell, the maximum power density reached ~0.33 W cm2 at 0.47 V.

The synergism of large surface area, multiscale porous structure, and good conductivity endows hierarchical carbon nanocages with high-level supercapacitive performances. Further nitrogen doping greatly improves the hydrophilicity, which boosts the supercapacitive performances to an ultrahigh specific capacitance of up to 313 F g(-1) at 1 A g(-1).

Fuel cells are clean, sustainable energy conversion devices for power generation, and they most commonly use platinum as the electrocatalyst. [1] However, Pt-based catalysts suffer from very limited reserves, high cost, and inactivation by CO poisoning; these are major obstacles that fuel cells have to overcome for commercialization. [1][2][3][4][5][6] Thus, exploring nonprecious metal or even metal-free catalysts to rival platinum in activity and durability is absolutely crucial, with a potentially revolutionary impact on fuel-cell technologies. Very recently, metal-free PEDOT [6] and nitrogen-doped carbon nanotubes (NCNTs) [7,8] have shown a striking electrocatalytic performance for the oxygen reduction reaction (ORR). These breakthroughs have activated an exciting field for exploring the advanced metal-free electrocatalysts and understanding the related mechanism.As one of the most important carbon nanostructures, carbon-based nanotubes have been widely studied as the support of electrocatalysts for fuel cells in recent years. [9][10][11][12] Recent progress involving doping carbon nanotubes (CNTs) with electron-rich nitrogen to transform CNTs into superb metal-free electrocatalysts for the ORR [7,8] has motivated our curiosity to examine the corresponding performance of its counterpart by doping CNTs with electron-deficient boron. Intuitively, the adsorption of O 2 on boron dopant should be quite easy owing to the large difference of electronegativity between boron and oxygen, which is the precondition for the subsequent O 2 dissociation. In this study, BCNTs with tunable boron content of 0-2.24 atom % were synthesized. The ORR onset and peak potentials shift positively and the current density increases noticeably with increasing boron content, indicating a strong dependence of the ORR performance on boron content. Moreover, the origin of the electrocatalytic activity of BCNTs including the role of the boron dopant has been revealed by density functional theory (DFT) calculations. The experimental and theoretical results provide a new strategy to explore carbon-based metal-free electrocatalysts that are significant to the development of fuel cells.Using chemical vapor deposition (CVD) with benzene, triphenylborane (TPB), and ferrocene as precursors and catalyst, BCNTs were synthesized with tunable boron content of 0-2.24 at % by using different TPB concentrations. BCNTs with boron content of 0.86, 1.33, and 2.24 at %, as determined by X-ray photoelectron spectroscopy (XPS), were denoted as B 1 CNTs, B 2 CNTs, and B 3 CNTs, respectively (Supporting Information, S1.

Supercapacitor electrode materials: Carbon nanocages are conveniently produced by an in situ MgO template method and demonstrate high specific capacitance over a wide range of charging-discharging rates with high stability, superior to the most carbonaceous supercapacitor electrode materials to date. The large specific surface area, good mesoporosity, and regular structure are responsible for the excellent performance.

3D few-layer graphene-like carbon with hierarchical open porous architecture is obtained by a new in situ Cu template method, leading to top-level supercapacitive performance, especially state-of-the-art power density. An effective new approach is demonstrated, which can extend the understanding of structure-performance relationships for many electrochemical energy-storage systems and form a significant complement to classical electrochemical impedance spectroscopy.

Fischer−Tropsch synthesis (FTS) is a classical topic of great significance because of the approach of post-petroleum times. For decades, people have attempted to develop iron-based FTS catalysts with high selectivity for lower olefins. By means of the anchoring effect and the intrinsic basicity of nitrogen-doped carbon nanotubes (NCNTs), iron nanoparticles were conveniently immobilized on NCNTs without surface premodification. The so-constructed Fe/NCNTs catalyst presents superb catalytic performance in FTS with high selectivity for lower olefins of up to 46.7% as well as high activity and stability. The excellent performance is well-correlated with enhanced dissociative CO adsorption, inhibition of secondary hydrogenation of lower olefins, and promoted formation of the active phase of χ-Fe 5 C 2 . All of these merits result from participation of the nitrogen, as revealed by our experimental characterization. These results may lead to a new strategy for exploring advanced FTS catalysts with abundant N-doped carbon nanostructures.