Efficient and methanol resistant noble metal free electrocatalyst for tetraelectronic oxygen reduction reaction

Directing oxygen reduction reaction selectivity towards hydrogen peroxide via electric double layer engineering

The electrochemical oxygen reduction reaction (ORR) has been recognized as a promising alternative for the sustainable production of H₂O₂. Here, we report a facile and effective strategy to promote ORR selectivity towards the 2e^- product H₂O₂via electric double layer engineering. Specifically, in a model system using immobilized cobalt phthalocyanine as the electrocatalyst, H₂O₂ selectivity has been improved from below 60% to over 93%, and the intrinsic activity for H₂O₂ formation has been enhanced by more than 3 times upon the introduction of a cationic surfactant (i.e., cetyltrimethylammonium bromide, CTAB) into the electrolyte. Based on detailed kinetics analysis, we conclude that the accelerated H₂O₂ formation rate results from the reduced charge transfer resistance in the rate limiting step and the promoted oxygen uptake rate. We propose that the electric field strength across the electric double layer is enhanced via the self-assembled single-tail cationic surfactant layer at the electrode/electrolyte interface, which is the origin of the enhancement of the 2e^- ORR performance.

Porous carbon-based metal-free monolayers towards highly stable and flexible wearable thermoelectrics and microelectronics

In the search for high mechanical strength and flexibility, ultrahigh semiconducting speed is crucial for the next generation of microelectronic and wearable electronics. Herein, we propose two 2D graphene-like macrocyclic complex carbon-based monolayers, namely g-MC-A and g-MC-B. Both monolayers are dynamically stable according to phonon dispersion and ab initio molecular dynamics simulations. The yield stress of these two layers reaches half that of graphene, revealing remarkably high mechanical strength. Besides, both monolayers are semiconductors. The electron mobility of g-MC-A is high: up to 10⁴ cm² V^-1 s^-1, comparable to black phosphorene. Furthermore, these two monolayers exhibit excellent inherent conductivity with anisotropic characteristics. Interestingly, an extra valley is observed near the conduction band edge for both layers, further simulation predicted both metal-free monolayers will exhibit ZT > 1, implying high thermoelectric performance. Therefore, these two C-based metal-free layers have promising applications in mechanical enhancement, microelectronics, wearable electronics and thermoelectric devices.

High-Level Oxygen Reduction Catalysts Derived from the Compounds of High-Specific-Surface-Area Pine Peel Activated Carbon and Phthalocyanine Cobalt

Non-platinum carbon-based catalysts have attracted much more attention in recent years because of their low cost and outstanding performance, and are regarded as one of the most promising alternatives to precious metal catalysts. Activated carbon (AC), which has a large specific surface area (SSA), can be used as a carrier or carbon source at the same time. In this work, stable pine peel bio-based materials were used to prepare large-surface-area activated carbon and then compound with cobalt phthalocyanine (CoPc) to obtain a high-performance cobalt/nitrogen/carbon (Co-N-C) catalyst. High catalytic activity is related to increasing the number of Co particles on the large-specific-area activated carbon, which are related with the immersing effect of CoPc into the AC and the rational decomposed temperature of the CoPc ring. The synergy with N promoting the exposure of CoNx active sites is also important. The Eonset of the catalyst treated with a composite proportion of AC and CoPc of 1 to 2 at 800 °C (AC@CoPc-800-1-2) is 1.006 V, higher than the Pt/C (20 wt%) catalyst. Apart from this, compared with other AC/CoPc series catalysts and Pt/C (20 wt%) catalyst, the stability of AC/CoPc-800-1-2 is 87.8% in 0.1 M KOH after 20,000 s testing. Considering the performance and price of the catalyst in a practical application, these composite catalysts combining biomass carbon materials with phthalocyanine series could be widely used in the area of catalysts and energy storage.

A novel cobalt and nitrogen co-doped mesoporous hollow carbon hemisphere as high-efficient electrocatalysts for oxygen reduction reaction

Exploring a cheap catalyst with effective activity for oxygen reduction reaction (ORR) to replace precious metal electrocatalysts has gained tremendous attention for several decades. In this study, we designed and synthesized cobalt and nitrogen supported on mesoporous hollow carbon hemisphere (Co/N/HCHs) nanocomposites by a facile and economical approach. Semisphere-shaped mesoporous hollow carbon is self-generated using silica particles as template, followed by a pyrolysis-etching process; and exhibits high electrical conductivity and high specific surface. The unique porous structure of carbon provides significant number of the abundant defective sites and shortens the mass transfer pathway, leading to a greatly enhanced electrocatalytic activity with mainly 4e^- reduction. Moreover, the synergistic effects of large electrochemically active areas and good electrical conductivity, resulting from the introduction of Co and N heteroatom, are the main reason for displaying outstanding ORR activity with a high half-wave potential of 0.8 V and the electron transfer numbers of 3.89. Furthermore, an excellent long-term stability (the current density retention of 87.0%) and superb methanol tolerance in alkaline medium are achieved. Undoubtedly, this demonstrates a potential way to strategically design the non-precious metal doped carbon catalysts for wider practical applications.