Search

In this work, we report a facile method to prepare P, N co‐doped porous carbon (PNPC) by the carbonization of covalent organic polymer (COP) used as efficient metal‐free electrocatalyst for hydrogen evolution reaction (HER), oxygen evolution reaction (OER) and oxygen reduction reaction (ORR). Overpotential is only 150 mV for the PNPC electrocatalyst to reach 10 mA cm−2 in the acidic medium due to the heteroatom dopants in the carbon matrix; meanwhile, stable HER activity is recorded during 5000 potential cycles. Additionally, overpotential is 343 mV for PNPC electrocatalyst to drive OER catalysis with 10 mA cm−2, which is comparable to the benchmarked IrO2 (320 mV). Similarly, PNPC electrocatalyst can achieve a Pt‐like ORR catalytic activity. The power density of the assembled rechargeable zinc‐air battery (ZAB) is 1.8 times higher than that of the commercial system (Pt/C−IrO2) and charge‐discharge voltage gap is well maintained during 20 h test, implying the high stability of the formed PNPC electrocatalyst. [ABSTRACT FROM AUTHOR]

As well known, heteroatom doped carbon material served as metal‐free electrocatalyst for hydrogen evolution (HER) and oxygen reduction reactions (ORR) particularly relies on the heteroatom doping level. Here, we report a 3D porous nitrogen doped carbon (PNC) electrocatalyst with superior HER and ORR electrocatalytic activities derived from the calcination of the discarded cigarette butt and dicyandiamide possessing a high nitrogen content (20 at%). PNC electrocatalyst only demands 143 mV versus RHE to achieve 10 mA cm−2 ascribed to the high nitrogen percentile in PNC electrocatalyst favorable for constructing successive active centers contributing to efficiently catalyzing HER. Ignorable degradation in HER activity observed after 10000 potential cycles as well as undetectable decay in HER performance recorded after 12 h operation indicate high stability of PNC electrocatalyst. Meanwhile, half‐wave potential of PNC electrocatalyst reaches 0.81 V versus RHE in 1 M KOH electrolyte. Additionally, stable ORR activity attained after 1000 potential cycles is indicative of high stability. A comparably high zinc‐air battery performance with maximum power density of 66 mW cm−2 is achieved by PNC electrocatalyst. This study highlights the importance of nitrogen doping level in metal‐free electrocatalyst for boosting HER and ORR activities. What? No metal! A 3D porous nitrogen doped carbon (PNC) electrocatalyst with superior HER and ORR electrocatalytic activities derived from the calcination of the discarded cigarette butt and dicyandiamide possessing a high nitrogen content (20 at%). [ABSTRACT FROM AUTHOR]

• Nitrogen atoms in Ni@NCNT facilitate the in-situ conversion of metallic Ni to Ni3+ species. • Nitrogen atoms in Ni@NCNT weaken the interaction between Ni3+ and CO 2 in urea oxidation. • 1.56 V is required to achieve 10 mA cm−2 in overall urea oxidation for Ni@NCNT. Urea electro-oxidation is an attractive and alternative anodic reaction in the electrochemical generation of hydrogen using wastewater ascribing to the low theoretical voltage and non-precious metal (nickel) catalyst for urea oxidation reaction (UOR); however, the sluggish UOR and poisoning of catalyst impede the practical application. Here, in this work, we synthesize a series of nickel nanoparticles embedded nitrogen doped carbon nanotubes (Ni@NCNT) and study the effect of nitrogen dopants on UOR catalytic activity. The nitrogen dopants can weaken the binding strength between CO 2 species and active sites resulting in alleviation of CO 2 poisoning; simultaneously, nitrogen dopants also promote the in-situ conversion of Ni3+ species facilitating UOR catalysis; as a result, electrocatalytic current density of 45.8 mA cm−2 is recorded for Ni@NCNT in 1 M KOH electrolyte with 0.5 M urea at 1.5 V vs. RHE, which is 3.8 fold better than commercial Pt/C (11.8 mA cm−2). Moreover, Ni@NCNT, due to the more nitrogen dopants, exhibits a comparable overpotential to commercial Pt/C for driving hydrogen evolution reaction (HER) catalysis in 1 M KOH electrolyte at high current density (400 mA cm−2). Subsequently, 1.56 V is demanded for overall UOR catalysis on Ni@NCNT with current density of 10 mA cm−2. This work offers useful information for designing a stable and efficient electrocatalyst for not only UOR but also electrochemical generation of H 2 from wastewater. [ABSTRACT FROM AUTHOR]

Highly active and stable electrocatalysts at low cost for hydrogen evolution reaction are essential for large scale hydrogen production. The Ni 3 P-Ni heterostructure confined in 3D networks of carbon nanotube (CNT) has been successfully prepared as the hydrogen evolution reaction (HER) electrode. The morphology and phase composition of Ni 3 P-Ni heterostructure are tunable by varying the acid pickling time. The Ni 3 P-Ni/CNT composite electrode with optimized Ni:Ni 3 P ratio of 22.29 wt% demonstrate high catalytic activity and excellent stability for HER. It demonstrates a comparable HER activity to the standard Pt electrode in alkaline solution, i.e., overpotentials of 116 vs 67 mV at 10 mA·cm−2 and Tafel slops of 59 vs 37 mV·dec−1. No degradation is observed after 1000 cyclic voltammetry (CV) cycles or 50 h operation under constant 0.3 V overpotential. • Pickling affects the morphology of heterogeneous structure and the content of Ni. • The Ni 3 P-Ni heterostructure was anchored to the carbon nanotube network by ball milling. • The electrode was prepared by mixing with PTFE and pressing. • The results show that Ni 3 P-Ni/CNT electrode has the best hydrogen evolution activity when the Ni/Ni 3 P ratio is 22.29 %. [ABSTRACT FROM AUTHOR]

• CoWO 4-x @C exhibits comparable HER activity to Pt/C in acidic and alkaline mediums. • CoWO 4-x @C requires only 295 mV overpotential to deliver 10 mA cm−2 in the OER test. • 1.57 V is required for CoWO 4-x @C to attain 10 mA cm−2 in alkaline water splitting. Development of earth-abundant, efficient and stable electrocatalysts for water splitting is of crucial importance for environmentally friendly energy conversion and storage. Here, we report an oxygen deficient cobalt tungstate nanoparticles with diameter of 8 nm (CoWO 4-x @C) as efficient bifunctional electrocatalyst for hydrogen evolution reaction (HER) and oxygen reduction reaction (OER), which exhibits comparable HER activity to commercial Pt/C with overpotentials of 32.5 mV and 46.8 mV vs. RHE to deliver current density of 10 mA cm−2 in acidic and alkaline mediums, respectively, ascribed to the rich oxygen vacancies facilitating the hydrogen adsorption and its relative recombination, respectively. Additionally, undetectable degradation is observed for CoWO 4-x @C after 10,000 potential cycles indicating high durability. Meanwhile, CoWO 4-x @C requires only 295 mV overpotential to deliver 10 mA cm−2 in the OER test, which is better than the benchmarking IrO 2 (313 mV). 1.57 V comparably lower than Pt/C-IrO 2 (1.59 V) is required for achieving the water splitting current density of 10 mA cm−2 without any degradation for 12 h. [ABSTRACT FROM AUTHOR]