Highly active oxygen reduction reaction on Fe-nanoclustered hierarchical porous carbon derived from CO2.

This work presents a highly active electrocatalyst of CO2-derived hierarchical carbon. It retains a high surface area and enables homogeneous insertion of Fe-N-C active sites for the oxygen reduction reaction. The electrocatalyst with a highly interconnected porous structure provides oxygen reduction reaction activity with an E1/2 difference of 10 mV and a high current density equivalent to Pt/C 20 wt%.

High-yield electrochemical hydrogen peroxide production from an enhanced two-electron oxygen reduction pathway by mesoporous nitrogen-doped carbon and manganese hybrid electrocatalysts.

Electrochemical hydrogen peroxide (H2O2) production by the direct two-electron (2e-) oxygen reduction reaction (ORR) has received much attention as a promising alternative to the industrially developed anthraquinone fabrication process. Transition metal (M) and nitrogen doped carbon (M-N-C, M = Fe or Co) catalysts are known to be active for four electron ORR pathways via two + two electron transfer, where the former is for the ORR and the latter for the peroxide reduction reaction (PRR). Here, we report mesoporous N-doped carbon/manganese hybrid electrocatalysts composed of MnO and Mn-Nx coupled with N-doped carbons (Mn-O/N@NCs), which have led to the development of electrocatalysis towards the 2e- ORR route. Based on the structural and electrochemical characterization, the number of transferred electrons during the ORR on the Mn-O/N@NCs was found to be close to the theoretical value of the 2e- process, indicating their high activity toward H2O2. The favored ORR process arose due to the increased number of Mn-Nx sites within the mesoporous N-doped carbon materials. Furthermore, there was a strong indication that the PRR is significantly suppressed by adjacent MnO species, demonstrating its highly selective production of H2O2 (>80%) from the oxygen electrochemical process. The results of a real fuel cell device test demonstrated that an Mn-O/N@NC catalyst sustains a very stable current, and we attributed its outstanding activity to a combination of site-dependent facilitation of 2e- transfer and a favorable porosity for mass transport.

Two-Dimensional Titanium Carbide MXene As a Cathode Material for Hybrid Magnesium/Lithium-Ion Batteries.

As an alternative to pure lithium-ion, Li+, systems, a hybrid magnesium, Mg2+, and Li+ battery can potentially combine the high capacity, high voltage, and fast Li+ intercalation of Li-ion battery cathodes and the high capacity, low cost, and dendrite-free Mg metal anodes. Herein, we report on the use of two-dimensional titanium carbide, Ti3C2Tx (MXene), as a cathode in hybrid Mg2+/Li+ batteries, coupled with a Mg metal anode. Free-standing and flexible Ti3C2Tx/carbon nanotube composite "paper" delivered ∼100 mAh g-1 at 0.1 C and ∼50 mAh g-1 at 10 C. At 1 C the capacity was maintained for >500 cycles at 80 mAh g-1. The Mo2CTx MXene also demonstrated good performance as a cathode material in this hybrid battery. Considering the variety of available MXenes, this work opens the door for exploring a new large family of 2D materials with high electrical conductivity and large intercalation capacity as cathodes for hybrid Mg2+/Li+ batteries.

Hierarchical cobalt-nitride and -oxide co-doped porous carbon nanostructures for highly efficient and durable bifunctional oxygen reaction electrocatalysts.

Here we report the preparation of hollow microspheres with a thin shell composed of mixed cobalt nitride (Co-N) and cobalt oxide (Co-O) nanofragments encapsulated in thin layers of nitrogen-doped carbon (N-C) nanostructure (Co-N/Co-O@N-C) arrays with enhanced bifunctional oxygen electrochemical performance. The hybrid structures are synthesized via heat treatment of N-doped hollow carbon microspheres with cobalt nitrate, and both the specific ratio of these precursors and the selected annealing temperature are found to be the key factors for the formation of the unique hybrid structure. The as-obtained product (Co-N/Co-O@N-C) presents a large specific surface area (493 m2 g-1), high-level heteroatom doping (Co-N, Co-O, and N-C), and hierarchical porous nanoarchitecture containing macroporous frameworks and mesoporous walls. Electronic interaction between the thin N-C layers and the encapsulated Co-N and Co-O nanofragments efficiently optimizes oxygen adsorption properties on the Co-N/Co-O@N-C and thereby triggers bifunctional oxygen electrochemical activity at the surface. The Co-N/Co-O@N-C nanohybrid exhibited a high onset potential of 0.93 V, and a limiting current density of 5.6 mA cm-2 indicating 4-electron oxygen reduction reaction (ORR), afforded high catalytic activity for the oxygen evolution reaction (OER) and even exceeded the catalytic stability of the commercial precious electrocatalysts; furthermore, when integrated into the oxygen electrode of a regenerative fuel cell device, it exhibited high-performance oxygen electrodes for both the ORR and the OER.

Boron-doped carbon-iron nanocomposites as efficient oxygen reduction electrocatalysts derived from carbon dioxide.

Developing cost-effective oxygen reduction reaction (ORR) catalysts is pivotal for development of fuel cells. While Fe-N-C catalysts were proposed for ORR, Fe-B-C catalysts have not been explored. This work introduces the B-doped carbon catalysts encapsulating iron cores using CO2 as a carbon source. The Fe-B-C catalysts show enhanced ORR activity and durability due to the iron core within the graphitic layers.