High Stability For Oxygen Reduction Reaction Research Articles

Boron modulating electronic structure of FeN4C to initiate high-efficiency oxygen reduction reaction and high-performance zinc-air battery

The biggest challenge is to develop a low cost and readily available catalyst to replace expensive commercial Pt/C for efficient electrochemical oxygen reduction reaction (ORR). In this research, closo-[B12H12]2− and 1,10-phenanthroline-iron complexes were introduced into the porous metal-organic framework by impregnation method, and further annealing treatment achieved the successful anchoring of single-atom-Fe in B-doped CN Matrix (FeN4CB). The ORR activity of FeN4CB is comparable to the widely used commercial 20 wt% Pt/C. Where the half-wave potential (E1/2) in alkaline medium up to 0.84 V, and even in the face of challenging ORR in acidic medium, the E1/2 of ORR driven by FeN4CB is still as high as 0.81 V. When FeN4CB was used as air cathode, the open circuit voltage of Zn-air battery reaches 1.435 V, and the power density and specific capacity are as high as 177 mW cm−2 and 800 mAh gZn−1 (theoretical value: 820 mAh gZn−1), respectively. The dazzling point of FeN4CB also appears in the high ORR stability, whether in alkaline or acidic media, E1/2 and limiting current density are still close to the initial value after 5000 times cycles. After continuously running the charge-discharge test for 220 h, the charge voltage and discharge voltage of the rechargeable zinc-air battery with FeN4CB as the air cathode maintained the initial state. Density functional theory calculations reveals that introducing B atom to Fe–N4–C can adjust the electronic structure to easily break O = O bond and significantly reduce the energy barrier of the rate-determining step resulting in an improved ORR activity.

PEDOT functionalized ZIF-67 derived Co-N-S triple-doped porous carbon for high-efficiency oxygen reduction

Herein, we report the use of poly(3,4-ethylenedioxythiophene) functionalized ZIF-67 (PEDOT/ZIF-67) as a precursor for preparing an efficient and precious metal-free oxygen reduction reaction (ORR) catalyst. The PEDOT/ZIF-67 precursor is subjected to pyrolysis at 800 °C and subsequent acidic etching with 1 M HCl to form Co-N-S triple-doped porous carbon (Co-N-S-PC), in which PEDOT functionalization inhibits the aggregation of the product, while the etching removes the excess Co metal and Co oxides, leading to exposure of more active sites and increase of transport channels. Electrochemical measurements reveal that the Co-N-S-PC catalyst obtained this way has outstanding activity, improved methanol-tolerance and high stability for ORR. Specifically, the limited current density (JL) and half-wave potential (E1/2) of the Co-N-S-PC are ~5.183 mA cm−2 and ~0.845 V, respectively, higher than those of commercial Pt/C (~5.049 mA cm−2 and 0.824 V). In addition, Co-N-S-PC is insensitive to methanol, without any responses to the injected 2 M CH3OH solution. Furthermore, the Co-N-S-PC displays better long-term stability, identified by its high activity retention (97.87%) and half-wave potential after chronoamperometry test for 5 h.

Probing Heteroatomic Dopant-Activity Synergy over Co3O4/Doped Carbon Nanotube Electrocatalysts for Oxygen Reduction Reaction.

Understanding and predicting how heteroatomic dopants of carbon nanotubes (CNTs)-based catalysts alter their catalytic performance at nanoscale is essential to design superior electrocatalysts for oxygen reduction reaction (ORR). This report describes findings of an investigation of the heteroatomic dopant-activity relationship for Co3O4/doped CNTs catalysts with different heteroatoms including N, O, and P atoms in ORR. By using an array of techniques to probe the structure and elementary valence of the catalysts, the incorporation of the Co3O4 nanoparticles can introduce defects into the doped CNTs, especially the N-CNTs, which should contribute to the generation of active sites. The Co3O4/N-CNTs are shown to exhibit both the highest ORR activity and stability compared with Co3O4/O-CNTs, Co3O4/P-CNTs, and Co3O4/CNTs, manifesting the synergistic correlation of Co3O4 nanoparticles, heteroatoms, and CNTs. This kind of synergy is assessed by density functional theory calculations based on the electronic properties and molecular orbitals. It is found that N, O, or P atoms can tune the charge distribution of CNTs by decreasing the lowest unoccupied molecular orbital-highest occupied molecular orbital energy gap, thus activating the adjacent C atoms. And the addition of Co3O4 will further redistribute the charge of CNTs from CNTs to Co3O4 toward enhanced ORR activity. Moreover, the Co3O4/N-CNTs catalyst exhibits a maximum structural stability due to the strong electronic interaction between Co2+ ions and N atoms, which is believed to result in its high ORR stability. Analysis of the results, along with a combined theoretical and experimental study, has provided implications for the design of catalysts with controlled activity and stability for ORR.