Excellent Oxygen Reduction Reaction Stability Research Articles

Boron-intercalation-triggered crystalline transition of Pd nanosheet assemblies for an enhanced oxygen reduction reaction

The development of effective and stable cathode electrocatalysts is highly desired for fuel cells. Controlling the composition and morphology of Pd-based materials can provide a great opportunity to improve their oxygen reduction reaction (ORR) performance. Here, we report the synthesis of hexagonal close-packed (hcp) Pd2B nanosheet assemblies (Pd2B NAs) via the boronation reaction between as-synthesized Pd NAs and N,N-dimethylformamide. The hcp Pd2B NAs with uniform pore distribution can provide sufficient active sites for ORRs. The insertion of B atoms can induce the phase transition from face-centered cubic structure to hcp structure, as the most thermodynamically stable phase in the Pd-B alloy, which is beneficial for enhancing the ORR stability and toxicity resistance. Therefore, the hcp Pd2B NAs exhibit superior mass activity, specific activity and excellent stability for ORR. The present strategy of boron-intercalation-triggered crystalline transition of Pd-based nanomaterials is valuable for the design of metal–nonmetal catalysts with enhanced performance.

Understanding the role of nitrogen and sulfur doping in promoting kinetics of oxygen reduction reaction and sodium ion battery performance of hollow spherical graphene

Here, a simple, economical one-step doping strategy is adopted to prepare N, S co-doped graphene hollow spheres (NSGHS). The NSGHS exhibits remarkable oxygen-reduction-reaction (ORR) activity with a high half-wave potential (E1/2) of 0.847 V vs. RHE and considerable long-term stability. When applied as anode materials for sodium-ion batteries (SIBs), it could deliver a high reversible capacity of 385 mAh g−1 at 500 mA g−1, excellent rate performance of 308 mAh g−1 at even 20 A g−1 and superior cycling performance at 10 A g−1 during 5000 cycles with negligible capacity fade. DFT calculation reveals that the doping of N and S endows the surrounding carbon with high positive charge and spin density, respectively, making them be highly active ORR catalytic sites except for S itself. Despite the possible oxidization of C–S–C active sites, the rest C atoms of NSGHS will still hold a considerably high catalytic activity superior to those of mono-doped or undoped cases. In addition, S doping will improve the binding between Na and graphene substrate to get a high capacity and N doping effectively curbs the rising of oxygen levels and oxidization of S in C–S–C active sites, thus the excellent stability for ORR and SIBs.

Exploiting S,N co-doped 3D hierarchical porous carbon with FeII–N4 moiety as an efficient cathode electrocatalyst for advanced Zn–air battery

Transition-metal-coordination N-doped carbon (M–N–C) materials have been explored extensively as oxygen reduction reaction (ORR) electrocatlysts, owing to the low price, high conductivity and superior electrocatalytic property. Herein, an effective templating approach is developed for synthesizing high density of FeII–N4 moiety dispersed in S,N-doped 3D hierarchical porous carbon (3DFe–S,N–C). Due to the high distribution of active sites, the large surface area and the abundant porosity, 3DFe–S,N–C displays a positive half-wave potential of 0.91 V and excellent ORR stability in alkaline medium. As demonstrated in cathode catalyst, 3DFe–S,N–C-based primary Zn–air battery (ZAB) can achieve a maximum power density of 160 mW cm−2 and specific energy density of 974 Wh kgZn−1. In addition, the as-prepared catalyst also exhibits a potential application in solid-state and flexible ZAB.

Pd9Au1@Pt/C core-shell catalyst prepared via Pd9Au1-catalyzed coating for enhanced oxygen reduction

The scarcity and poor long-term stability of Pt has greatly hindered its commercial application as oxygen reduction reaction (ORR) catalyst. In this work, carbon-supported Pd9Au1 alloy particles with a Pd/Au molar ratio of 9:1 synthesized by using an ethylene glycol-based reduction method were used to catalyze ethanol oxidation to coat Pd9Au1 core with Pt atomic layers to synthesize Pd9Au1@Pt/C catalyst. Physical characterization shows that the as-synthesized Pd9Au1@Pt/C catalysts present a well-defined core-shell structure and the surface Pt layers can be well controlled by tuning the amount of Pt precursor added during synthesis. Electrochemical characterization shows that among the synthesized catalysts Pd9Au1@Pt2/C with 2 atomic Pt layers exhibits the best activity and excellent stability for ORR, as evidenced by its even increased half-wave potential after 10000 potential cycles between 0.6 and 1 V in O2-saturated 0.1 M HClO4 solution. This enhanced ORR activity and stability of Pd9Au1@Pt2/C catalyst can be attributed to the compressive strain and stabilizing effect of Pd9Au1 core on Pt shell.

Efficient electrocatalyst of Pt–Fe/CNFs for oxygen reduction reaction in alkaline media

Transition metal iron-based catalysts are promising electrocatalysts for oxygen reduction reaction (ORR), and they have the potential to replace noble metal catalysts. The one-dimensional of carbon nanofibers with tubular structure can effectively promote the electrocatalytic activity, which facilitates electron transport. Herein, the Pt–Fe/CNFs were synthesized by electrospinning and subsequent calcination. Benefiting from the advantages of one-dimensional structure, Pt–Fe/CNFs-900 with fast electrochemical kinetics and excellent stability for ORR with excellent onset of 0.99 V, a low Tafel slope of 62 mV dec−1 and high limiting current density of 6.00 mA cm−2. Long-term ORR testing indicated that the durability of this catalyst was superior to that of commercial Pt/C in alkaline electrolyte. According to RRDE test, the ORR reaction process of Pt–Fe/CNFs-900 was close to four-electron transfer routes.