Highly Active and Stable Fe/Co/N Co-doped Carbon-Anchored Pd Nanoparticles for Oxygen Reduction Reaction

Synthesis of MnOOH and its application in a supporting hexagonal Pd/C catalyst for the oxygen reduction reaction

With the expansion of global energy problems and the deepening of research on oxygen reduction reaction (ORR) in alkaline media, the development of low cost and high electrocatalytic performance catalysts has become a research hotspot. In this study, a hexagonal Pd-C-MnOOH composite catalyst was prepared by using the triblock copolymer P123 as the reducing agent and protective agent, sucrose as the carbon source and self-made MnOOH as the carrier under hydrothermal conditions. When the Pd load is 20% and the C/MnOOH ratio is 1 : 1, the 20% Pd-C-MnOOH-1 : 1 catalyst obtained by the one-step method has the highest ORR activity and stability in the alkaline system. At 1600 rpm, the limiting diffusion current density and half-wave potential of the 20% Pd-C-MnOOH-1 : 1 electrocatalyst are -4.78 mA cm-2 and 0.84 V, respectively, which are better than those of the commercial 20%Pd/C catalyst. According to the Koutecky-Levich (K-L) equation and the linear fitting results, the electron transfer number of the 20%Pd-C-MnOOH-1 : 1 electrocatalyst for the oxygen reduction reaction is 3.8, which is similar to that of a 4-electron process. After 1000 cycles, the limiting diffusion current density of the 20%Pd-C-MnOOH-1 : 1 catalyst is -4.61 mA cm-2, which only decreases by 3.7%, indicating that the 20%Pd-C-MnOOH-1 : 1 catalyst has good stability. The reason for the improvement of the ORR performance of the Pd-C-MnOOH composite catalyst is the improvement of the conductivity of the carbon layer formed by original carbonization, the regular hexagonal highly active Pd particles and the synergistic catalytic effect between Pd and MnOOH. The method of introducing triblock copolymers in the synthesis of oxides and metal-oxide composite catalysts is expected to be extended to other electrocatalysis fields.

Enhancement of Electrocatalytic Oxygen Reduction Reaction and Oxygen Evolution Reaction by Introducing Lanthanum Species in the Carbon Shell

The development of cost-effective non-noble metal electrocatalysts for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) opens up the possibility for sustainable energy systems. Herein, we report a surface overcoating strategy with lanthanum organic complex (La-OC) as the precursor to prepare lanthanum species (La-SPc) encapsulated in nitrogen, fluorine, and sulfur self-doped porous carbon (NFS-PC) composites (La-SPc@NFS-PC) for efficient ORR and OER. The La-SPc is introduced not only as a promoter to increase the electrochemical stability of the La-SPc@NFS-PC catalysts but also to tailor the electronic structure of NFS-PC due to the unique electrochemical properties of La-SPc. In addition, the integration of La-SPc and NFS-PC can improve the electronic conductivity of composites by inducing electron redistribution and lowering the band gap, which is advantageous in enhancing the kinetics of charge transfer. Simultaneously, benefiting from the optimized porous structure and positive cooperation of La-SPc with NFS-PC shells, the obtained La-SPc@NFS-PC-3 delivers robust bifunctional ORR/OER activities and stabilities. More importantly, the Zn-air battery (ZAB) assembled with La-SPc@NFS-PC-3 demonstrates an outstanding power density (181.1 mW cm-2) and long cycling life, outperforming the commercial Pt/C. This work offers a rational approach to preparing high-efficiency rare-earth-based catalysts and provides potential applications in ZABs.

Zn-Induced Synthesis of Porous Fe-N,S-C Electrocatalyst with Iron-Based Active Sites Containing Sulfides, Oxides and Nitrides for Efficient Oxygen Reduction and Zinc-Air Batteries

There is an urgent need to design and synthesize non-noble metal electrocatalysts (NNMEs) for the replacement of platinum-based electrocatalysts to enhance the sluggish oxygen reduction reaction (ORR) for Zn-air batteries and fuel cells. Herein, Fe-N,S-C materials were fabricated through two steps: first, reprecipitating hemin by adjusting the pH and, then, decorating it with melamine and cysteine in the presence of Zn2+. The resulting Fe-N,S-C-950 (Zn) was prepared after pyrolysis at 950 °C. Using this method, abundant iron-based active species with good dispersion were obtained. The fabrication of more micropores in Fe-N,S-C-950 (Zn) plays a positive role in the improvement of ORR activity. On comparison, Fe-N,S-C-950 (Zn) outperforms Fe-N,S-C-950 and Fe-N-C-950 (Zn) with respect to the ORR due to its larger specific surface area, porous structure, multiple iron-based active sites and N- and S-doped C. Fe-N,S-C-950 (Zn) achieves outstanding ORR performances, including a half-wave potential (E1/2) of 0.844 V and 0.715 V versus a reversible hydrogen electrode (RHE) in 0.1 M KOH and 0.1 M HClO4 solution, respectively. In addition, Fe-N,S-C-950 (Zn) shows an outstanding Zn-air battery performance with an open-circuit voltage (OCV) of 1.450 V and a peak power density of 121.9 mW cm-2, which is higher than that of 20 wt% Pt/C. As a result, the as-prepared electrocatalyst in this work shows the development of the Zn-assisted strategy combined with the assembly of porphyrins as NNMEs for the enhancement of the ORR in both alkaline and acidic solutions.

Atomic Fe/Zn anchored N, S co-doped nano-porous carbon for boosting oxygen reduction reaction

Dual-single-atom catalysts are well-known due to their excellent catalytic performance of oxygen reduction reaction (ORR) and the tunable coordination environment of the active sites. However, it is still challengable to finely modulate the electronic states of the metal atoms and facilely fabricate a catalyst with dual-single atoms homogeneously dispersed on conductive skeletons with good mass transport. Herein, atomic FeN_x/ZnN_x sites anchored N, S co-doped nano-porous carbon plates/nanotubes material (Fe_0.10ZnNSC) is rationally prepared via a facile room-temperature reaction and high-temperature pyrolysis. The as-prepared Fe_0.10ZnNSC catalyst exhibits a positive onset potential of 0.956 V, an impressive half-wave potential of 0.875 V, excellent long-term durability, and a high methanol resistance, outperforming the benchmark Pt/C. The outstanding ORR performance of Fe_0.10ZnNSC is due to its unique nanoarchitecture: a large specific surface area (1092.8 cm² g^-1) and well-developed nanopore structure ensure the high accessibility of active sites; the high conductivity of the carbon matrix guarantees a strong ability to transport electrons to the active sites; and the optimized electronic states of FeN_x and ZnN_x sites possess good oxygen intermediate adsorption/desorption capacity. This strategy can be extended to design and fabricate other non-precious dual-single-atom ORR catalysts.

Iron/cobalt-decorated nitrogen-rich 3D layer-stacked porous biochar as high-performance oxygen reduction air-cathode catalyst in microbial fuel cell

Developing low-cost and high-efficiency oxygen reduction reaction (ORR) catalysts is crucial to the commercial application of microbial fuel cell (MFC). Herein, Fe/Co-decorated nitrogen-rich three-dimensional (3D) layer-stacked porous biochar (Fe/Co-NC-x) have been synthesized from silk gel through secondary carbonization of activated carbons which firstly adsorbed metal ions. The multilayer porous structure of Fe/Co-NC-3 contributes to construction of high specific surface area (576 m² g^-1), large pore volume (1.27 cm³ g^-1) and many defect structure (I_D/I_G = 1.004). As expected, with Fe/Co synergistic effect, Fe/Co-NC-3 exhibits excellent ORR performance through 4e^- pathway with good methanol resistance. In addition, the performance of MFC using Fe/Co-NC-3 as air-cathode catalyst is more prominent with higher maximum power density (1059.62 ± 30.00 mW m^-2) compared to that using NC (668.19 ± 9.84 mW m^-2) and commercial Pt/C catalyst (957.33 ± 10.50 mW m^-2). Therefore, Fe/Co-NC-3 should be a prospective catalyst in the practical application of fuel cells and other energy devices.

MIL-88-Derived N and S Co-Doped Carbon Materials with Supplemental FeSx to Enhance the Oxygen Reduction Reaction Performance

To overcome the drawbacks of the single N-doped carbon materials, the further development of dual-heteroatoms (N and S) co-doped electrocatalysts is highly anticipated. Herein, N, S-doping and Fe-based carbon materials were synthesized by pyrolyzing a metal–organic framework (MIL-88) with the addition of N-/N, and S-containing ligands (chitosan and L-Cysteine) in the case of iron salt. The resulting electrocatalyst heat-treated at 850 °C (FeNSC-850) displays superior oxygen reduction reaction (ORR) performances to MIL-88-850, with an overall electron transfer number of 3.97 and a minor yield of HO2-% (<2.6%). In addition to the comparable activity to commercial Pt/C in catalyzing the ORR in alkaline solution, the FeNSC-850 also shows higher stability, with a slight decline in half-wave potential (∆E1/2 = 15 mV) after 5000-cycle scanning of cyclic voltammetry. In view of the multiple Fe-based active sites, the additional S doping within FeNSC-850 creates more FeSx active sites for boosting the ORR performances in alkaline solution. 

Cobalt nanoparticles supported on microporous nitrogen-doped carbon for efficient catalytic transfer hydrogenation reaction between nitroarenes and N-heterocycles

Catalytic transfer hydrogenation reaction between nitroarenes and saturated N-heterocycles to simultaneously synthesize value-added anilines and unsaturated N-heterocycles is attractive due to its low-cost, atomic economic, and environmental-friendly properties. Herein, we...