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We report a straightforward strategy to design efficient N doped porous carbon (NPC) electrocatalyst that has a high concentration of easily accessible active sites for the CO2 reduction reaction (CO2RR). The NPC with large amounts of active N (pyridinic and graphitic N) and highly porous structure is prepared by using an oxygen‐rich metal–organic framework (Zn‐MOF‐74) precursor. The amount of active N species can be tuned by optimizing the calcination temperature and time. Owing to the large pore sizes, the active sites are well exposed to electrolyte for CO2RR. The NPC exhibits superior CO2RR activity with a small onset potential of −0.35 V and a high faradaic efficiency (FE) of 98.4 % towards CO at −0.55 V vs. RHE, one of the highest values among NPC‐based CO2RR electrocatalysts. This work advances an effective and facile way towards highly active and cost‐effective alternatives to noble‐metal CO2RR electrocatalysts for practical applications. [ABSTRACT FROM AUTHOR]

It is of increasing importance to explore new low-cost and high-activity electrocatalysts for oxygen reduction reaction (ORR), which have had a substantial impact across a diverse range of energy conversion system, including various fuel cell and metal-air batteries. Although engineering carbon nanostructures have been widely explored as a candidate class of Pt-based ORR electrocatalysts owing to their proved high activity, outstanding stability, and ease of use, there still remains a daunting challenge to develop high activity metal-free electrocatalysts in pH-universal electrolyte system. Here, a reliable and controllable route amenable to prepare nitrogen-doped porous carbon (NPC) with high yields and exceptional quality is described. The as-prepared NPC shows advantages of high activity, high durability, and methanol-tolerant as an efficient pH-universal electrocatalyst for ORR, showing comparable or even better activity as compared with the commercial Pt/C catalysts not only in alkaline media but also in acidic and neutral electrolyte. Systematic electrochemical studies, combining with density functional theory calculation, demonstrate the unique nitrogen-doping species and favorable pores in the as-designed NPC synergistically contribute to the significantly improved catalytic activity in pH-universal medium. The present work potentially presents an important breakthrough in developing ORR electrocatalysts for various fuel cells. [ABSTRACT FROM AUTHOR]

• Ni@NiO-Cu@CuO/NCS is prepared from MOF material via direct calcination process. • Material favors to human urine urea oxidation and groundwater NO 3 − reduction. • Presence of M2+/M3+ redox couple offers better bifunctional catalytic activity. • Substitution of ORR with NRR launches a new branch of fuel cell named UNFC. Though direct urea fuel cells (DUFCs) show promising potential for green energy generation, the practical feasibility of its on-site installation is yet encumbered by the sluggish electrokinetics and low-value product (H 2 O) of oxygen reduction reaction (ORR). We here report the design and synthesis of a bifunctional hybrid electrocatalyst of nitrogen-doped carbon sheets supporting Ni@NiO-Cu@CuO composites (Ni@NiO-Cu@CuO/NCS) via direct calcination of Ni- and Cu-containing metal organic frameworks (MOFs). The as-derived nanohybrid shows impressively high catalytic performance towards urea oxidation reaction (UOR) in alkali and nitrate reduction reaction (NRR) in acidic electrolyte, which inspire us to set up a urea-nitrate fuel cell (UNFC). Owing to the excellent electrochemical characteristics behaviour of prepared nanostructures, the fabricated UNFC simultaneously exhibits improved fuel cell performance of 22.55 ± 2.3 mW cm−2 and degrade the urine and nitrate at the anode and cathode, respectively. The presented innovative electrochemical device may open up a prime step for the development of renewable UNFC for simultaneous green energy generation and N-containing waste removal. [ABSTRACT FROM AUTHOR]