High Peak Power Density Research Articles

Mesoporous carbon promoting the efficiency and stability of single atomic electrocatalysts for oxygen reduction reaction

Single-atom Fe–N–C electrocatalysts are attracting more attentions as one most promising transition metal based single-atom catalyst towards the oxygen reduction reaction (ORR). However, the inaccessibility of internal Fe-Nx active sites and insufficient stability hinder their large-scale application. Herein, a facile benzoate-assisted self-template strategy which could dramatically enhance the oxygen reduction reaction catalytic performance and stability of ZIF-8 derived atomically dispersed Fe–N–C catalysts (Fe-SA/Meso-C) is developed. The sodium benzoate used in the present work is effective for promoting the formation of Fe–N–C catalysts with denser accessible active sites as well as mesopores with diameters ranging from 2.5 to 5 nm. These structural advantages make the synthesized Fe-SA/Meso-C catalysts afford excellent electrocatalytic performance for the ORR in 0.1 M KOH with a positive half-wave potential (E1/2) of 0.926 V vs. RHE and exceptionally high kinetic current density (Jk) of 92.5 mA cm−2 at 0.85 V. Beyond that, Fe-SA/Meso-C shows outstanding long-term stability with over 90% activity retain after 90 h chronoamperometry i-t test as well as superior tolerance to methanol crossover. More importantly, the assembled zinc-air battery with Fe-SA/Meso-C as the cathode material achieves a high peak power density of 166.2 mW cm−2 and a high specific capacity of 776.1 mA h g−1. Our results reveal that small mesopores in atomically dispersed Fe–N–C electrocatalysts could facilitate mass transport, increase the accessibility of active sites and optimize the interface between electrolyte and carbon matrix, thus optimizing their electrocatalytic performance for the ORR. This work paves a way to the design and synthesis of stable single-atom electrocatalysts with optimized structure, electrochemical performance and promising applications.

Insight towards kinetics and stability of carbon supported Pd–Y2O3 as cathode catalyst for polymer electrolyte fuel cells

Pd–Y 2 O 3 on carbon (Pd–Y 2 O 3 /C) in different mass ratios of Pd to Y 2 O 3 (1:1, 2:1, 3:1) were prepared and subjected as cathode electrocatalyst for polymer electrolyte fuel cells (PEFC). X-ray diffraction (XRD) and transmission electron microscopy (TEM) were used to determine the structure, crystalline size and dispersion of Pd–Y 2 O 3 /C respectively. The electrochemical characterizations of the electrocatalysts were evaluated from Cyclic Voltammetry (CV) and Linear Sweep Voltammetry (LSV). These electrocatalysts were evaluated for their catalytic activity towards oxygen reduction reaction (ORR) in fuel cell. Pd 2 –Y 2 O 3 /C catalyst shows higher power density of 325 mW cm −2 than Pd 1 –Y 2 O 3 /C, Pd 3 –Y 2 O 3 /C and Pd/C. • Various atomic ratios of Pd–Y 2 O 3 /C prepared and evaluated as ORR catalyst for PEFC. • Pd 2 –Y 2 O 3 /C as a cathode catalyst shows high peak power density of 325 mW cm −2 . • Pd 2 –Y 2 O 3 /C exhibits higher ORR activity due to SMSI effect.

An Imidazolium Type Ionic Liquid Functionalized Ether-Free Poly(terphenyl piperidinium) Membrane for High Temperature Polymer Electrolyte Membrane Fuel Cell Applications

Development of high temperature polymer electrolyte membranes is essential for advanced energy conversion and storage technologies. Herein, an imidazolium type ionic liquid (BPMIm) with a long side-chain of 5-bromopentyl is synthesized and employed as the quaternization reagent for ether-free poly(p-terphenyl-co-N-methyl-piperidine) (PTP). Grafting the flexible long side-chain imidazolium group into the ether-free polymer backbone not only improves the polymer solubility in organic solvents but also provides acid-base interaction sites for the following phosphoric acid doping that supports proton conductivity at above 100 °C. Compared with pure and iodomethane quaternized PTP membranes (i.e. PTP and PTP-Me), the prepared imidazolium ionic liquid grafted PTP membrane (i.e. PTP-PMIm) exhibits an enhanced phosphoric acid uptake and hence a superior anhydrous proton conductivity of 138 mS cm−1 at 180 °C. The technical feasibility of the PTP-PMIm membrane is demonstrated in H2-air fuel cells at temperatures from 160 °C–200 °C, which reaches a high peak power density of around 456 mW cm−2 at 200 °C at ambient pressure.

High Space Efficiency Hybrid Nanogenerators for Effective Water Wave Energy Harvesting

AbstractWater wave energy is a vital renewable‐energy resource, but it is less developed due to the characteristics of water wave with low and varying frequency. Herein, a bifilar‐pendulum coupled hybrid nanogenerator (BCHNG) module, which includes an electromagnetic generator (EMG), two piezoelectric nanogenerators (PENGs), and two multilayer‐structured triboelectric nanogenerators (TENGs), is incorporated into a vessel‐like platform for wave energy harvesting. The combination of the lightweight TENG and the heavy PENG and EMG can not only increase the ability of power take‐off to capture water wave energy, but also improve the space utilization rate of BCHNG module and facilitate the design of the floating wave energy collecting device. Furthermore, the BCHNG module can harvest the kinetic energy and gravitational potential energy of the water wave at the same time, which benefits from the two degrees of swing freedom of the bifilar‐pendulum. Importantly, thanks to the accurate geometric design and the reasonable utilization of space, the BCHNG module achieves a high peak power density of 358.5 W m−3. The findings not only provide a novel method for the large‐scale development of blue energy, but also offer an opportunity for the development of self‐powered marine resources.

Designing superior bifunctional electrocatalyst with high-purity pyrrole-type CoN4 and adjacent metallic cobalt sites for rechargeable Zn-air batteries

Developing cost-effective and high-efficient bifunctional electrocatalyst for both oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) is essential for rechargeable Zn-air battery application. However, achieving high-active dual sites for bifunctional oxygen electrocatalysis in a single catalyst, as well as determining the decisive active sites for OER and ORR to explore the synergistically catalytic mechanism remain challenges. Herein, we propose a catalyst consisting of high-purity pyrrole nitrogen anchored cobalt single-atom (CoN4) and adjacent metallic cobalt sites (Cop@CoNC) for explicit research of dominated active sites. The obtained Cop@CoNC exhibits superior electrocatalytic activity with a small overpotential difference of 0.68 V between OER potential at 10 mA cm−2 and ORR half-wave potential, outperforming commercial noble-metal based catalysts. Electrochemical measurements and theoretical simulations verify the pyrrole-type CoN4 and adjacent metallic cobalt are separately decisive active sites for ORR and OER activities. Simultaneously, metallic cobalt regulates electron distribution of CoN4 moiety to improve ORR activity. Importantly, the rechargeable liquid and flexible solid-state Zn-air batteries using Cop@CoNC as air electrode catalysts possess high peak power densities of 188.8 and 121.8 mW cm−2, respectively. Our findings provide a feasible strategy to design high-performance multifunctional catalysts for rechargeable Zn-air batteries application.

In-Situ Silica Xerogel Assisted Facile Synthesis of Fe-N-C Catalysts with Dense Fe-Nx Active Sites for Efficient Oxygen Reduction.

In the past decade, atomically dispersed Fe active sites (coordinated with nitrogen) on carbon materials (FeNC) have emerged rapidly as promising single-atom catalysts (SACs) for the oxygen reduction reaction (ORR) to substitute precious group metal (PGM) catalysts, owing to their earth abundance and low cost. Nonetheless, the production of highly active FeNC SACs is largely restricted by material cost, low product yield and difficulty of microstructure design. Herein, the authors demonstrate a facile in-situ xerogel (ISG) assisted synthetic strategy, using cheap materials, to construct FeNC SACs (ISG FeNC). The porous silica xerogel, formed in-situ with the FeNC precursors, encourages the emergence of enormous micropores/mesopores and homogeneous confinement/protection to the precursors during pyrolysis, benefiting to the formation of abundant accessible active sites (27.6 × 1019 sites g-1 ). Correspondingly, the ISG FeNC exhibits excellent ORR activity with a half-wave potential (E1/2 = 0.91V) in alkaline medium. The Zn-air battery assembled using the ISG FeNC SACs as the bifunctional catalyst of air cathode, demonstrates commendable performance with high peak power density of 249.1mW cm-2 and superior long-term stability (660 cycles with 220 h). This work offers an economic and efficient way to fabricate PGM-free SACs for diverse applications.

Efficiently catalyzed sea urchin-like mixed phase SmMn2O5/MnO2 for oxygen reduction reaction in zinc-air battery

In this work, sea urchin-like SmMn2O5/MnO2 is synthesized by the hydrothermal method. Compared with SmMn2O5, SmMn2O5/MnO2 has a half wave potential of 0.82 V (vs RHE), which shows excellent electrocatalytic activity of oxygen reduction reaction (ORR) in the alkaline media. More importantly, the composite of SmMn2O5/MnO2 shows higher number of electron transfers, better stability of ORR, and stronger methanol-tolerant ability comparison with the commercial catalyst of Pt/C. The remarkable ORR activity is due to the formation of abundant oxygen vacancies and Mn3+, which are beneficial to the adsorption of oxygen species and the activation of O-O bond. The sea urchin-like morphology increases the specific surface area, and the tip-like synapses play an essential role in charge accumulation and rapid transfer. Moreover, the rechargeable zinc-air battery made of SmMn2O5/MnO2 not only has a high peak power density, but also has excellent cycle stability of 450 h in long-term charge discharge measurement.

Ultrathin anion exchange membranes with an improved OH− transfer rate for high-performance AEMFCs

A new freestanding ultrathin AEMs were synthesized with high mechanical strength and anion conductivity by precise polymer topological regulation. The assembled AEMFCs have high peak power density (1.8 W cm−2) and long-term stability (∼140 h).

High peak power density and low mechanical stress photonic-band-crystal diode laser array based on non-soldered packaging technology

High peak power density and low mechanical stress photonic-band-crystal diode laser array based on non-soldered packaging technology

Herbal residue-derived N, P co-doped porous hollow carbon spheres as high-performance electrocatalysts for oxygen reduction reaction under both alkaline and acidic conditions

Development of carbon-based oxygen reduction reaction (ORR) catalysts with performance superior to noble metals across a wide pH range has been a formidable challenge. Herein, porous hollow carbon spheres co-doped with N, P (NH3-NPCS-900) is directly synthesized from the herbal residues of Lasiosphaera seu Calvatia (LSC). Critically, the N content was significantly enhanced in the presence of ammonia (NH3) and formed a hierarchical porous structure and a large specific surface area (984.7 m2 g−1). With the synergistic effect of these contributions, the NH3-NPCS-900 catalyst exhibit excellent ORR catalytic activity across acidic (E1/2 = 0.615 V) and alkaline solutions (E1/2 = 0.862 V). Zn-air batteries with NH3-NPCS-900 exhibit high peak power density (188 mW cm−2) and better cycle durability (>180 h), showing its potential and promise in applications. This study provides valuable direction and insight into how to develop porous carbon with highly efficient ORR catalytic activity from biomass.

A promising Ruddlesden–Popper oxide cathode for both proton-conducting and oxygen ionic-conducting solid oxide fuel cells

A novel Nd1.8La0.2Ni0.74Cu0.21Ga0.05O4+δ cathode is developed for a proton-conducting solid oxide fuel cell with a high peak power density of 1.264 W cm−2 at 800 °C.

A bimetallic-activated MnO2 self-assembly electrode with a dual heterojunction structure for high-performance rechargeable zinc-air batteries

A major challenge in developing zinc-air batteries (ZABs) is to exploit suitable cathodes to efficiently accelerate the key electrocatalytic processes involved. Herein, a bifunctional oxygen catalytic self-supported MnO2-based electrode is designed that displays superior oxygen reduction and evolution reaction performance over noble metal electrodes with a total overpotential of 0.69 V. In addition, the as-synthesized NiCo2O4@MnO2/carbon nanotube (CNT)-Ni foam self-supported electrode can be directly used as an oxygen electrode without externally adding carbon or a binder and shows reasonable battery performance with a high peak power density of 226 mW cm-2 and a long-term charge-discharge cycling lifetime (5 mA for 160 h). As expected, the rapid oxygen catalytic intrinsic kinetics and high battery performance of the NiCo2O4@MnO2/CNTs-Ni foam electrode originates from the unique three-dimensional hierarchical structure, which effectively promotes mass transfer. Furthermore, the CNTs combined with Ni foam form a unique “meridian” conductive structure that enables rapid electron conduction. Finally, the abundant Mn3+ active sites activated by bimetallic ions shorten the oxygen catalytic reaction distance between the active sites and reactant and reduce the surface activity of MnO2 for the O, OH, and OOH species. This work not only offers a high-performance bifunctional self-supported electrode for ZABs but also opens new insights into the activation of Mn-based electrodes.

Performance improvement of ultra-low Pt proton exchange membrane fuel cell by catalyst layer structure optimization

• Improvement of catalyst layer structure was achieved with mild oxidized multiwalled carbon nanotubes. • A high peak power density of 1.23 W·cm −2 was obtained at an ultra-low loading of 120 μg·cm −2 Pt and PtRu. Reducing the loading of noble Pt-based catalyst is vital for the commercialization of proton exchange membrane fuel cell (PEMFC). However, severe mass transfer polarization loss resulting in fuel cell performance decline will be encountered in ultra-low Pt PEMFC. In this work, mild oxidized multiwalled carbon nanotubes (mMWCNT) were adopted to construct the catalyst layer, and by varying the loading of carbon nanotubes, the catalyst layer structure was optimized. A high peak power density of 1.23 W·cm −2 for the MEA with mMWCNT was obtained at an ultra-low loading of 120 μg·cm −2 Pt/PtRu (both cathode and anode), which was 44.7% higher than that of MEA without mMWCNT. Better catalyst dispersion, low charge transfer resistance, more porous structure and high hydrophobicity of catalyst layer were ascribed for the reasons of the performance improvement.

A hierarchically porous Fe-N-C synthesized by dual melt-salt-mediated template as advanced electrocatalyst for efficient oxygen reduction in zinc-air battery

The reasonable design of porous structures is important but usually overlooked for nonprecious metal ORR catalysts. In this study, a facile dual melt-salt-mediated templating method is developed to prepare a Fe-N-C catalyst with tailored porous framework. The ZnCl2 and NaCl are employed to construct abundant micropores and promote the transformation of partial micropores to mesopores, respectively, reasonably forming a 3D hierarchically porous framework. The catalyst demonstrates a satisfactory surface area (1605 m2/g), promoting mass transport and exposure of FeN4 sites. Interestingly, the dual melt-salt templates avoid rapid loss of nitrogen during pyrolysis, thus enhancing Fe-N4 active center density. Therefore, the obtained Fe-N-C material presents outstanding ORR performance in both alkaline and acid media, as well as good stability. The advances of this catalyst are further proved in liquid and solid-state Zn-air battery, with nice discharge stability and high peak power densities.

Synthesis of Tangled Iron‐Nitrogen Co‐doped Carbon Nanosheets through a Dopamine Coordination Strategy for the Oxygen Reduction Reaction

AbstractDeveloping efficient, economical, and durable transition metal atom‐dispersed catalysts to boost the sluggish oxygen reduction reactions (ORRs) is crucial for the practical metal‐air batteries. Herein, a facile dopamine‐coordination strategy was developed to obtain tangled Fe, N co‐doped ultrathin carbon nanosheets (donated as tangled Fe−N−C nanosheets), which can be utilized as high‐performance ORR electrocatalysts. Benefited from the unique hierarchical porous structures and abundant Fe−Nx active sites, the tangled Fe−N−C nanosheets exhibited excellent ORR activity in alkaline medium with more positive half‐wave potential (0.88 V vs. RHE) than 20 wt % Pt/C (0.84 V vs. RHE). Meanwhile, the tangled Fe−N−C nanosheets exhibit excellent long‐term stability and good tolerance to methanol crossover. When applying the Fe−N−C nanosheets as the cathode catalyst for primary zinc‐air batteries (ZABs), the assembled cells exhibit high open circuit voltage (∼1.43 V), high peak power density (∼89 mW cm−2) and large specific capacity of 801 mA h g−1.

Nafion membranes for e-fuel cell applications

ABSTRACT Direct liquid fuel cells have been extensively studied and regarded as a promising candidate for wide commercialization among the various existing energy conversion technologies. However, their real applications still encounter many challenges mostly arising from the sluggish reaction kinetics of the liquid fuels. Recently, a novel system, powered with an electrically rechargeable liquid fuel (e-fuel), named the e-fuel cell has been presented with superior cell performance. However, studies regarding ion exchange membrane, which is an indispensable component in the liquid e-fuel cell, are still limited. Herein, a comparative study has been conducted to evaluate the performance of four Nafion series membranes. These membranes with different thicknesses have been examined and characterized at both membrane level and cell level. It is found that the thickness of membrane shows critical effects on its area resistance, as well as vanadium-ion crossover rate, which further significantly affects the e-fuel cell performance. Overall, the thinnest membrane (Nafion 211) is revealed to be preferable for the purpose of attaining a high peak power density, while the thickest membrane (Nafion 117) provides a lower self-discharge rate for the cell.

Flexible, compressible, versatile biomass-derived freestanding carbon monoliths as binder- and substrate-free tri-functional electrodes for solid-state zinc-air batteries and overall water splitting

Highly flexible and compressible biomass-derived freestanding monoliths are directly utilized as binder- and substrate-free tri-functional electrodes for the wearable electronic devices. The introduction of Co nanoparticles, nanoclusters, and single atoms onto biomass-derived monoliths leads to the additional growth of CNTs for ensuring the interconnectivity of 3D cellulose-derived carbon network. Thus, superb flexibility and/or compressibility as well as high-efficiency tri-functional activity are achieved simultaneously. The alkaline water electrolyzer with monolithic electrodes requires only a potential of 1.56 V to generate hydrogen at a current density of 50 mA cm−2 for over 120 h. Furthermore, the quasi-solid-state zinc-air batteries(ZABs) exhibit a high peak power density of 175.5 mW cm−2, and an optimal charge-discharge overpotential with a remarkably small voltage gap (∆V) of 0.27 V at 5 mA cm−2. The excellent charge-discharge cycle stability even under bending and compression conditions demonstrates its high potential for emerging next-generation electronics devices.

Molten-Salt-Assisted Synthesis of Nitrogen-Doped Carbon Nanosheets Derived from Biomass Waste of Gingko Shells as Efficient Catalyst for Oxygen Reduction Reaction

Developing superior efficient and durable oxygen reduction reaction (ORR) catalysts is critical for high-performance fuel cells and metal–air batteries. Herein, we successfully prepared a 3D, high-level nitrogen-doped, metal-free (N–pC) electrocatalyst employing urea as a single nitrogen source, NaCl as a fully sealed nanoreactor and gingko shells, a biomass waste, as carbon precursor. Due to the high content of active nitrogen groups, large surface area (1133.8 m2 g−1), and 3D hierarchical porous network structure, the as-prepared N–pC has better ORR electrocatalytic performance than the commercial Pt/C and most metal-free carbon materials in alkaline media. Additionally, when N–pC was used as a catalyst for an air electrode, the Zn–air battery (ZAB) had higher peak power density (223 mW cm−2), larger specific-capacity (755 mAh g−1) and better rate-capability than the commercial Pt/C-based one, displaying a good application prospect in metal-air batteries.

Rational Design of Two-Layer Fe-Doped PrBa0.8Ca0.2Co2O6−δ Double Perovskite Oxides for High-Performance Fuel Cell Cathodes

A solid oxide fuel cell (SOFC) offers an attractive route to convert chemical energy into electrical energy; however, its commercial application is often limited by the large mismatch in thermal expansion coefficients (TECs) between the cathode and electrolyte and the insufficient activity of cathodes. Fe-doped PrBa0.8Ca0.2Co2O6−δ (PBCC) are promising cathode materials due to their high conductivity and excellent oxygen-reduction activity, in which Fe doping in PBCC can decrease the TEC to achieve better compatibility with the electrolyte, but excessive Fe will inhibit the oxygen kinetics. Here, we construct a two-layer PBCC cathode (TLC), which consists of a high Fe content layer with good thermal compatibility to electrolytes and a low Fe content layer with high ionic and electronic conductivity. Compared to homogeneous PBCC electrodes, the cell with TLC has a lower activation energy and a higher peak power density (1259.3 mW cm–2 at 700 °C). Meanwhile, it exhibits admirable stability up to 200 h in constant potential mode (0.8 V), and importantly, no discernible degradation is observed in further stability tests in the constant current mode (444 mA cm–2) for 200 h. The results reveal that the TLC based on double perovskite Fe-doping isostructural oxide is a promising candidate electrode for SOFC.

Optimizing Microenvironment of Asymmetric N,S-Coordinated Single-Atom Fe via Axial Fifth Coordination toward Efficient Oxygen Electroreduction.

Single-atom catalysts (SACs) are attractive candidates for oxygen reduction reaction (ORR). The catalytic performances of SACs are mainly determined by the surrounding microenvironment of single metal sites. Microenvironment engineering of SACs and understanding of the structure-activity relationship is critical, which remains challenging. Herein, a self-sacrificing strategy is developed to synthesize asymmetric N,S-coordinated single-atom Fe with axial fifth hydroxy (OH) coordination (Fe-N3 S1 OH) embedded in N,S codoped porous carbon nanospheres (FeN/SC). Such unique penta-coordination microenvironment is determined by cutting-edge techonologies aiding of systematic simulations. The as-obtained FeN/SC exhibits superior catalytic ORR activity, and showcases a half-wave potential of 0.882V surpassing the benchmark Pt/C. Moreover, theoretical calculations confirmed the axial OH in FeN3 S1 OH can optimize 3d orbitals of Fe center to strengthen O2 adsorption and enhance O2 activation on Fe site, thus reducing the ORR barrier and accelerating ORR dynamics. Furthermore, FeN/SC containing H2 O2 fuel cell performs a high peak power density of 512mW cm-2 , and FeN/SC based Znair batteries show the peak power density of 203 and 49mW cm-2 in liquid and flexible all-solid-state configurations, respectively. This study offers a new platform for fundamentally understand the axial fifth coordination in asymmetrical planar single-atom metal sites for electrocatalysis.