The development of effective bifunctional catalysts for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is significant for energy conversion systems, such as Li–air batteries, fuel cells, and water splitting technologies. Herein, a Chlorella-derived catalyst with a nestlike framework, composed of bamboolike nanotubes that encapsulate cobalt nanoparticles, has been prepared through a facile pyrolysis process. It achieves perfect bifunctional catalysis both in ORR and OER on a single catalyst. For our optimal catalyst Co/M-Chlorella-900, its ORR half-wave potential is positively shifted by 40 mV compared to that of a commercial Pt/C catalyst, and the overpotential at 10 mA cm–2 for the OER is 23 mV lower than that of a commercial IrO2/C catalyst in an alkaline medium. This superior bifunctional catalytic performance is benefited from the simultaneous increase of pyridinic N sites for ORR and graphitic N sites for OER. In addition, N-doped carbon-encapsulated Co nanoparticles improve both ORR and OER performance by forming new active centers. The unique nestlike carbon nanotube framework not only afforded highly dense ORR and OER active sites but also promoted the electron and mass transfer. Our catalyst also displays notable durability during the ORR and OER, making it promising for use in ORR/OER-related energy conversion systems.Keywords: activity sites; biomass; nitrogen-doped carbon nanotubes; oxygen evolution reaction; oxygen reduction reaction;

•The performance of MEA can be enhanced by introducing N doped CNTs in CL and GDL.•The MEA with NCNTs in both CL and GDL simultaneously achieves best enhancements.•The current density at 0.7 V and 0.6 V is enhanced by 67 and 33% by adding NCNTs.•The max power density of our optimal MEA reaches 997 mW cm−2, enhanced by 28%.The performance of the proton exchange membrane fuel cell (PEMFC) is significantly improved through introducing nitrogen-doped carbon nanotubes (NCNTs) into the catalyst layer (CL) and microporous layer (MPL) of the membrane electrode assembly (MEA), it reveals by SEM images that the NCNTs are uniformly dispersed in CL and MPL, resulting in the more plenty of porosity, higher surface area, better conductivity, and better prevention of the layer cracks. The BET surface area and pore volume of MPL are increased by 88% and 77% respectively with the addition of 20 wt% of NCNTs in MPL. The membrane electrode assembly (MEA) with adding 20 wt% NCNTs both in cathode CL and in cathode GDL can yield the best cell performance. At a cell temperature of 70 °C and 30 psi back pressures, the current density is up to 1000 mA cm−2 at 0.7 V and 1600 mA cm−2 at 0.6 V, and the max power density reaches 997 mW cm−2.The MEA prepared by introducing nitrogen-doped CNTs (NCNTs) both in cathode CL and in cathode GDL exhibits excellent performance at cell temperature of 70 °C and 100% RH, the current density can be up to 1000 mA cm−2 at 0.7 V and 1600 mA cm−2 at 0.6 V, respectively, and the maximum power density reaches 997 mW cm−2, which is much higher than that of the MEA without NCNTs addition (781 mW cm−2).Download high-res image (210KB)Download full-size image

High-performance ferric phosphate (FePO4), with well-defined ellipsoid morphology and uniform particle size distribution, is successfully fabricated via a green spray drying method with formic acid as additive. It is found that the added formic acid plays a crucial role for the formation of the well-distributed FePO4 particles. Benefited by the outstanding structure and properties of ferric phosphate prepared above, a high performance of lithium iron phosphate (LiFePO4) has been prepared. It exhibits high capacity, especially at high charging/discharging rate (158.4 mAh g−1 at 0.2 C and 107.3 mAh g−1 at 10 C), and excellent cycling stability (without capacity fading after cycling for 200cycles at 1 C). All these impressive electrochemical performance could be ascribed to the FePO4 precursor, and further attributed to the addition of formic acid, which may play as a template, resulting in the well-defined morphology, uniform particles size distribution, hierarchical pore structure, and high surface area of the ferric phosphate.

Transition metal nitrides have recently attracted significant interest as electrocatalysts for the oxygen reduction reaction (ORR) owing to their low electrical resistance and good corrosion resistance. In this paper, we describe the preparation of a Nb-based binary nitride material with a porous nanogrid morphology/structure. The catalyst exhibited good catalytic activity and high stability towards oxygen reduction. We also intensively investigated the effect that doping with a second transition metal had on the performance of the catalyst. We found that the ORR activity of NbN could be enhanced significantly by enriching the d electrons of Nb through doping with a second transition metal, and that doping with cobalt resulted in the best improvement. Our optimal catalyst, Nb0.95Co0.05N, had an ORR activity ∼4.6 times that of NbN (current density @ 0.6 V vs. the RHE). XPS results revealed that Co doping increased the proportion of Nb in a low-valence state, which may be one of the most important reasons for the enhanced performance. Another important reason is the high surface area resulting from the porous nanogrid morphology. As transition metal doping is an attractive way to enhance the activity of nitride catalysts, our work may provide an effective pathway to achieve this.

A biocompatible nanovalve attached to the surface of MCM-41 mesoporous nanoparticles is designed to release encapsulated guest molecules controllably under pH activation. This nanovalve system is comprised of α-cyclodextrin (α-CD) rings that encircle p-anisidino linkers, and can be tuned to respond under specific pH conditions through chemical modification of the linkers. One of the distinctive features of this functional nanovalve system lies in its excellent bio-stability and durability in cell culture medium solution, the binding between the α-CD and p-anisidino groups was not interrupted or disintegrated by the proteins in the DMEM solution without adjusting the pH value. Luminescence spectroscopy demonstrates that the on-command pH-activated system displays very good bio-stability—no drug leakage at pH ∼7.4 and excellent drug release performance not only in H2O but also in cell culture medium at pH ∼5.5.Graphical abstractA biocompatible pH-responsive drug delivery nanovalve system was designed, synthesized, and tested. The on-command pH-activated system displayed very good stability—no drug leakage at pH ∼7.4 and excellent drug release performance not only in H2O but also in cell culture medium at pH ∼5.5.Highlights► A biocompatible pH-responsive nanovalve was designed based on MCM-41 mesoporous nanoparticles. ► The nanoparticles possess uniform small size and good monodispersion. ► The on-command pH-activated system displays very good bio-stability. ► No drug leakage was observed in cell culture medium solution before the pH was tuned. ► The nanovalve system exhibits excellent drug release performance not only in H2O but also in cell culture medium at pH ∼5.5.

Transition metal nitrides have recently attracted significant interest as electrocatalysts for the oxygen reduction reaction (ORR) owing to their low electrical resistance and good corrosion resistance. In this paper, we describe the preparation of a Nb-based binary nitride material with a porous nanogrid morphology/structure. The catalyst exhibited good catalytic activity and high stability towards oxygen reduction. We also intensively investigated the effect that doping with a second transition metal had on the performance of the catalyst. We found that the ORR activity of NbN could be enhanced significantly by enriching the d electrons of Nb through doping with a second transition metal, and that doping with cobalt resulted in the best improvement. Our optimal catalyst, Nb0.95Co0.05N, had an ORR activity ∼4.6 times that of NbN (current density @ 0.6 V vs. the RHE). XPS results revealed that Co doping increased the proportion of Nb in a low-valence state, which may be one of the most important reasons for the enhanced performance. Another important reason is the high surface area resulting from the porous nanogrid morphology. As transition metal doping is an attractive way to enhance the activity of nitride catalysts, our work may provide an effective pathway to achieve this.