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Developing metal-free catalysts possessing high oxygen reduction reaction (ORR) catalytic activity and splendid stability has become one of the most attractive topics in contemporary society. In this study, Triarrhena sacchariflora panicles were hydrothermally treated in KOH aqueous solution. The KOH activation was simplified. After carbonization and nitrogen doping process, the N-doped carbon material was obtained. The material presents a 3D interconnected hierarchical porous structure and an excellent ORR catalytic activity (E 1/2 = 0.83 V), along with a high stability (6% loss of current density after 10,000 s) in alkaline media. Compared to the commercial Pt/C catalyst (20 wt%), the catalyst exhibits a similar ORR catalytic activity and much higher stability in alkaline media. Taking this method can not only dispose of the biowaste well but also reduce the amount of KOH compared with the traditional KOH activation method, resulting in low cost and little environmental pollution. Image 1098958 [ABSTRACT FROM AUTHOR]

Abstract Exploring efficient non-platinum catalysts for the oxygen reduction reaction (ORR) instead of platinum-based catalysts is vital for reducing costs of fuel cells or metal-air batteries. A Prussian blue/N-doped porous carbon (PB/NPC) nanocomposite catalyst for ORR was synthesized by a novel method of one-step high-temperature pyrolyzing the mixture of the casein extracted with ferric ions, potassium hydroxide and melamine. The PB nanocubes were embedded in the NPC, and the particle size of PB nanocubes was less than 100 nm. The presence of PB effectively reduced the production of hydrogen peroxide, and the PB/NPC catalyst exhibited high catalytic activity such as more positive onset-potential (of ∼0.93 V vs. RHE), large diffusion limiting current density (5.79 mA cm−2) close to Pt/XC-72 (20%) catalyst and good stability in alkaline media due to the stable binding structure and the synergistic effect of PB nanocubes and NPC. The synthetic strategy of the PB/NPC provides a facile and effective method for the preparation of non-platinum catalysts for energy conversion and storage applications. Graphical abstract Image 1 [ABSTRACT FROM AUTHOR]

Nitrogen-doped mesoporous carbon (NMC) was synthesized via pyrolysis of cobalt-containing casein obtained by extraction from pure milk with the auxiliary of cobalt ions. The cobalt element in casein promoted specific surface area and N element doping amount of casein-derived porous carbon. The N-doped porous carbon obtained by carbonization at 800 °C (NPC-800) possessed a specific surface area of ∼886.7 m 2 g −1 , and the mesoporous size was centered at 2.7 and 7 nm. X-ray photoelectron spectroscopy analysis showed that the nitrogen content of NPC-800 was 3.29 at%. The NPC-800 was explored as a symmetric supercapacitor, which exhibited specific capacity of 380 F g −1 at a current density of 0.5 A g −1 , 218 F g −1 at a current density of 20 A g −1 , and high capacitance retention of 91.3% after charging/discharging 5,000 cycles. [ABSTRACT FROM AUTHOR]

A 3-D covalently crosslinked N-doped porous carbon/holey graphene composite (NPC/HG) was synthesized by carbonizing the precursor mixture of casein, graphene oxide (GO) and KOH. The polypeptide and amino acid produced by hydrolysis of casein in KOH solution could react with GO, which was conducive to the uniform coating of the NPC precursor on GO and the mutual crosslinking of GO. After carbonization, NPC with a high specific surface area was uniformly coated in the two-dimensional plane of graphene, and graphene was bonded into a 3-D structure by the "solder"-NPC, moreover, the KOH was an activator of NPC and also reacted with carbon atoms of GO to form holes in the carbonization process. The NPC/HG-2 showed the high specific surface area of 1135.3 m2 g−1, the rich hierarchical pore structure, and the high nitrogen doping amount of 6 at%. Used in the symmetric supercapacitor, the NPC/HG-2 exhibited the energy density of 29.33 Wh kg−1 at a power density of 42.75 kW kg−1, lower internal resistance and the excellent rate performance due to its unique internal pore structure. Moreover, the voltage of the NPC/HG-2 symmetric quasi-solid-state supercapacitor was up to 1.4 V. Image 1 • The 3-D N-doped porous carbon/holey graphene (NPC/HG) was designed and synthesized. • The reaction of GO and casein hydrolysate was the key to the synthesis of NPC/HG. • Graphene achieved covalently cross-linking through the "solder" —casein-derived NPC. • The NPC/HG showed a good 3-D cross-linked structure and a high specific surface area. • The NPC/HG symmetric quasi-solid-state supercapacitor showed high voltage and rate performance. [ABSTRACT FROM AUTHOR]