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Direct borohydride fuel cells (DBFCs) exhibit the potential for a wide range of applications due to their high energy and power density; however, the hydrolysis of BH 4 − significantly limits the use of DBFCs. In this paper, PdNi x -B/carbon nanotubes (PdNi x -B/CNTs) (x = 0, 0.3, 0.6, 0.9) composites have been prepared by a chemical reduction method in which PdNi x -B nanoparticles of approximately 3.5 nm are grown on the surface of carbon nanotubes. A cell was assembled with PdNi x -B/CNTs as the anode catalyst, a polymer fibre membrane (PFM) as a substitute for the Nafion membrane and LaNiO 3 as the cathode catalyst. The results show that the Ni element displays an ability to balance the competition between the hydrolysis and oxidation of BH 4 − . A peak power density of 105 mW cm −2 (x = 0.9) was achieved at 25 °C. However, the highest fuel efficiency of 69% was achieved at x = 0.3, and the corresponding power density was 87 mW cm −2 , which represents the best comprehensive performance of these DBFCs. [ABSTRACT FROM AUTHOR]

The fundamental challenge of trimetallic single-atoms catalysts stems from the difficulty in supporting the coexistence of different metals with their unique physicochemical features. Here, the trimetallic single-atoms electrocatalyst is constructed as a model system to explore electrocatalytic ORR/OER. The tri-metal (Fe, Co, and Ni) single-atoms loaded on nitrogen-carbon framework exhibits superior ORR/OER kinetics (E 1/2 = 0.927 V, E j =10 = 1.56 V). The flexible zinc-air batteries generate excellent power density and durability (62 mW cm−2 and 200 h at −15 °C, 291.2 mW cm−2 and 250 h at room temperature). Density functional calculations confirm that the trimetallic synergy effect outperform mono- and bimetallic effects, yielding adsorption strength close to 0. This paper describes an intuitionistic descriptor where ΔE OH* displays a volcano relationship with ORR overpotential, and establishes a generalized strategy for efficient bifunctional oxygen electrocatalyst while comprehensively understanding the structure-mechanism-activity relationship. [Display omitted] • Tri-metal incorporated nitrogen-carbon catalysts possesses high density and well dispersed tri-metal single atom sites. • Fe 3% Co 3% Ni 9% -NC1000 display outstanding ORR/OER performance. • The descriptor ΔE OH* displays a volcano relationship with ORR overpotential. • Flexible zinc-air batteries assembled with Fe 3% Co 3% Ni 9% -NC1000 generate superior power density and durability. [ABSTRACT FROM AUTHOR]

[Display omitted] Highly efficient electrochemical catalysts for oxygen reduction reactions (ORRs) are urgently needed for various energy conversion and storage devices to overcome sluggish ORR kinetics. Here, N,O-codoped carbon spheres with uniform mesopores and a high specific surface area were used as supports for decorating Co 3 O 4 nanoparticles via a facile immersion route. In addition to the benefit of ions and gas mass transfer, the abundant mesopores present in the three-dimensional (3D) carbon spheres also confine and isolate the Co 3 O 4 nanoparticles growing in it, which help to provide rich Co 3 O 4 active sites. The resulting hybrid material exhibits superior ORR activity in terms of even-better half-wave potential and stability than that of commercial Pt/C (40 wt%) in 0.1 M KOH electrolyte. To verify its catalytic activity, the hybrid material was employed as the cathode catalyst in a flexible solid-state zinc-air battery, which achieves a high power density of 227 mW cm−2; this power density is much higher than that of a Pt/C catalytic zinc-air battery (133 mW cm−2) under identical conditions. The improvement in catalytic activity in both aqueous and nonaqueous electrolytes can be attributed to the abundant active sites of the entangled Co 3 O 4 nanoparticles, as well as the novel N,O-codoped carbon structure. [ABSTRACT FROM AUTHOR]

The functional combination of riboflavin and activated carbon successfully introduced a significant redox reaction in the activated carbon, increasing the specific capacitance of the material and significantly improving the rate performance. Potential control significantly enhances the cycling stability of AC/VB2. [Display omitted] • AC/VB2 has a low charge/discharge plateau of −0.65 to −0.9 V (vs. Hg/HgO). • AC/VB2 as a negative electrode shows high specific capacitance (419.1 F g−1) and outstanding rate performance. • Potential control significantly enhances the cycling stability of AC/VB2. • An AC/VB2(–)||LDH(+) device delivers a high energy density of 58.5 Wh kg−1 and a high power density of 27,410 W kg−1. Pseudocapacitive materials are used to increase the energy density of supercapacitors, but their rate performance and cycling stability are frequently unsatisfactory. Herein, we report a riboflavin-functionalized activated carbon (AC/VB2) as a negative electrode with high specific capacitance (419.1 F g−1) and outstanding rate performance. The potent combination of VB2 and AC renders VB2 insoluble in alkaline liquids and fully exploits its redox characteristics. VB2 contributes additional redox reactions to AC and its reaction plateau is from −0.65 to −0.9 V (vs. Hg/HgO), favoring the storage of large amounts of energy. Based on the detailed analysis of the surface state of the material during the reaction, a strategy to improve cycling stability by controlling the charge/discharge potential window is proposed, which can effectively inhibit the desorption and overreaction of VB2, thus greatly enhancing cycling stability. The electrode can be operated stably for 100,000 cycles without any decline at high current densities. An AC/VB2(–)||LDH(+, Co-doped Ni(OH) 2) device delivered a high energy density of 58.6 Wh kg−1 at a power density of 686 W kg−1 and a high power density of 27,410 W kg−1 at an energy density of 13.2 Wh kg−1. This work offers a practical manual for making high–energy pseudocapacitive negative electrodes and enhancing their cycling stability. [ABSTRACT FROM AUTHOR]

The functional combination of methylene blue and activated carbon successfully introduced a significant redox reaction in the activated carbon, increasing the specific capacitance of the material and significantly improving the rate performance. The methylene blue adsorbed on the surface of activated carbon enables fast proton-coupled electron transfer. [Display omitted] • Anthracite can be activated at low temperature and show large specific surface area. • Oxygen groups could effectively contribute the pseudo-capacitance to AC. • The π-π binding endows AC/MB excellent electrochemical properties. • The optimized AC/MB as positive can deliver ultrahigh energy and power density. • Mathematical simulation can optimize the ratio of positive to negative electrodes. Supercapacitors are desired to deliver high power and energy density concurrently, and the introduction of a redox reaction is an effective strategy to improve their capacitive performance. Herein, methylene blue (MB) with redox was employed to functionalize coal-based activated carbons (ACs) as electrode materials for energy storage. The optimized AC shows a high specific capacitance of 408.1 F g−1 in 6 M KOH, deriving from the contribution of the electrical double-layer capacitance of pores and pseudocapacitance of oxygen groups. Interestingly, pure MB shows no capacitive performance mainly due to its low conductivity, while the optimized composite of AC adsorbed MB (AC/MB) surpasses the pure MB and optimized AC in any capacitive performance, displaying a relationship of mutual promotion based on functional combination. The best AC/MB sample exhibits a high specific capacitance of 431.8 F g−1 at 1 A g−1, and 356.1 F g−1 (82.5%) at an ultrahigh current density of 180 A g−1, implying an excellent rate performance. Aiming to deliver maximum energy density, an accurate universal method is proposed to match the mass ratio of negative to positive. The optimized asymmetric supercapacitor AC/MB(+) || AC(-) delivers an energy density of 11.0 Wh kg−1, a power density up to 15.3 kW kg−1 and a high capacity retention rate of 96.3% after 10,000 cycles, displaying good chemical stability. This work proposes a promising strategy for ultrafast store/release energy at high energy density, and also provides an application direction for AC and MB. [ABSTRACT FROM AUTHOR]

• The power density of the activated carbon reached 8.8 Wh ∙ kg−1 at 0.25 kW ∙ kg−1. • The activated carbons are rich in carbonyl groups and quinone type oxygen. • The oxygen-rich activated carbons were prepared without oxidation by strong acid. • The fluxing effect of KOH as activation agent was discovered for the first time. Heteroatom-doped activated carbons are ideal materials for energy storage devices. In this work, a series of nitrogen/oxygen codoped activated carbons with an inverse opal-like structure derived from cellulose diacetate are successfully synthesized through hydrothermal reaction and subsequent chemical activation during which the fluxing effect of KOH is discovered for the first time. The introduction of nitrogen and intrinsic oxygen (especially carbonyl and quinone groups) contributes to additional pseudocapacitance. The experimental results show that the obtained product delivers 400.3 F · g−1 at a current density of 1 A · g−1 in a three-electrode system and achieves extraordinary capacity retention of 90% after 10,000 charge-discharge cycles at 5 A · g−1. The energy density reaches as high as 8.8 Wh · kg−1 at a power density of 0.25 kW · kg−1 as symmetric supercapacitors, indicating a promising electrode material for high performance supercapacitors. The simple and cost-effective method requires no extra oxidation and excessive urea and thus provides new approaches for the future design of electrode materials. [ABSTRACT FROM AUTHOR]

[Display omitted] • Honeycomb-like nanoporous carbons with dopants and tunable pore sizes were prepared. • The pore sizes can greatly influence the oxygen reduction activity. • FANC-12 receives a high power density of 174.1 mW cm−2 in a flexible Zn-air battery. • Theory calculation demonstrates that pyridinic N species are the active sites. Metal-free carbon nanomaterials doped with heteroatoms are deemed as promising alternatives to platinum for O 2 reduction in fuel cell and metal-air batteries. To boost the catalytic activity, construction of nanoporous structured carbons with exposed active sites and improved ions/gas mass transport capability is the main research objective. However, controlled preparation of carbon materials with uniform morphology and tunable nanopore sizes is still a great challenge. Herein, a novel furfuryl alcohol-derived, N, O-codoped nanoporous carbon (FANC) with honeycomb-like structure is reported, which possesses high uniformity and controllable pore sizes. Four FANCs with various pore sizes were carefully prepared and their electrocatalytic activity toward oxygen reduction reaction (ORR) were systematically investigated. Among the four FANCs, the one with a pore size of 12 nm (FANC-12) receives the best ORR performance, which is close to that of commercial Pt/C in alkaline electrolyte. A high power density of 174.1 mW cm−2 was obtained with FANC-12 as cathode catalyst in a flexible solid-state zinc-air battery. Calculation by density functional theory reveals the possible structure of this novel N, O-codoped carbon material and also demonstrates that pyridinic N species are the active sites, which is consistent with the experimental result. [ABSTRACT FROM AUTHOR]

• A high-efficient and cost-effective direct methanol fuel cell is proposed. • The peak power density is higher than both electrodes with noble catalysts. • Faradic efficiency of 85.1% and energy efficiency of 42.2% were obtained. • Enhanced O 2 adsorption and transfer capacity were obtained on cathode. • The half-wave potential of Fe 2 O 3 /Mn 2 O 3 outperforms commercial Pt/C. The development of power density and energy conversion efficiency of direct methanol fuel cells (DMFCs) is of great significance. This study presents a high-efficiency passive DMFC consisting of hetero-structured Fe 2 O 3 /Mn 2 O 3 as the cathode catalyst, PtRu/C as the anode catalyst and polymer fiber membrane (PFM) as the electrolyte membrane. The peak power densities reached up to 60.6, 121.2 and 186.6 mW cm−2 at 20, 50 and 70 °C, respectively, which was approximately 2.7 times greater than a normal cell composed of commercialized Nafion membrane and Pt/C cathode catalyst at 20 °C. Faradic efficiency of 85.1% and energy efficiency exceeding 42.2% were obtained. Herein, Fe 2 O 3 /Mn 2 O 3 displays framework structure with edge lengths of 1 to 2 μm homogeneous micro-cubes. A synergistic effect between α-Fe 2 O 3 and α-Mn 2 O 3 matrix in Fe 2 O 3 /Mn 2 O 3 significantly enhances its oxygen reduction reaction (ORR) catalyzed activity. α-Fe 2 O 3 with abundant oxygen vacancies could store and release O 2 through the transformation of Fe3+/Fe2+ redox couple. The three-dimensional mesoporous channel structure of Fe 2 O 3 /Mn 2 O 3 could act as effective mass transfer reactors, in which O 2 and electrolyte is uninhibited accessed to active sites. On the other hand, numerous heterogeneous interfaces can boost electron transfer efficiency, which is investigated using the electron transfer number, narrow band gap and lower charge transfer resistance. The output performance and the energy conversion efficiency of DMFCs is considerably improved through boosting oxygen and charge transfer capability in cathode. Overall, our result provides a promising strategy to fabricate high-efficient and cost-effective fuel cells for the enhanced power conversion. [ABSTRACT FROM AUTHOR]