High Peak Power Density Research Articles

Integrating Dual-Interfacial Liquid Metal Based Nanodroplet Architectures and Micro-Nanostructured Engineering for High Efficiency Solar Energy Harvesting.

Broadband strong absorption of solar light over a wide range of angles, low heat loss, and excellent structural reliability are of significance for enhancing solar harvesting of photothermal materials; however, it remains a challenge to achieve these attributes simultaneously. Herein, a tailored photothermal composite nanodroplet (LMP-rGO) featured with dual-interface, which comprises liquid metal (LM) core with polydopamine (PDA) photothermal middle layer of tunable thickness and reduced graphene oxide (rGO) shell, is particularly prepared. Thermal-insulating PDA coating and light-absorbing carbonaceous shell allow it to synergistically suppress heat loss and reinforce photon absorptivity. To maximize photothermal conversion and photon harvesting yield on solar light, inspired by light trapping architecture, a three-dimensional (3D) stepped micropyramid grating array framework is tactfully designed to ameliorate light coupling. Utilizing the scalability and cost-effectiveness of the poly(vinyl alcohol) (PVA), the flexible 3D-structured PVA/LMP-rGO absorbers are successfully constructed via a controllable casting molding strategy. As a proof-of-concept, the developed micrograting absorber exhibits a desirable combination of strong broadband selective light absorption (94.9% for parallel to the grating direction and 97.3% for perpendicular to the grating direction), superior photothermal conversion effect (89.4%), high heat flux density, and fascinating mechanical properties. Also, an efficient and steady solar-driven thermoelectric generator (STEG) system for real-time solar-heat-electric conversion, with its high peak power density of 245.9 μW cm-2 under one sun irradiation, is further displayed, making an important step to rationally design LM-based nanocomposite droplets for solar energy harvesting.

A-site doping enabled higher-oxygen-vacancy cobalt-free layered perovskite cathode for higher-performing protonic ceramic fuel cells

Cobalt-free layered perovskite as a promising mixed ionic electronic conductor cathode has shown outstanding performance in conventional oxygen-ion conducting solid oxide fuel cells (O–SOFCs), but not in next-generation proton-conducting solid oxide fuel cells (H–SOFCs) due to insufficient oxygen vacancy so far. We propose a facile A-site doping strategy to enable higher-oxygen-vacancy cobalt-free layered perovskite cathode for higher-performing protonic ceramic fuel cells at reduced temperatures. As proof of concept, two different typical A-site doping of mixed-rare-earth Nd and alkali-metal K in PrBaFe1.9Zn0.1O5+δ are chosen as potential H–SOFC cathode materials. Pr0.8Nd0.2BaFe1.9Zn0.1O5+δ (PNBFZ) and PrBa0.9K0.1Fe1.9Zn0.1O5+δ (PBKFZ) layered perovskite cathodes were synthesized using a nitrate-gel combustion method. Both PNBFZ and PBKFZ have a layered perovskite structure and are chemically compatible with protonic BaZr0.1Ce0.7Y0.2O3−δ (BZCY) electrolyte. Both Nd and K doping dramatically improve the electrical conductivities under operation temperatures. Compared with PBKFZ, PNBFZ shows a lower average thermal expansion coefficient (TEC) of 13.9✕10−6 K−1, being thermally compatible with the BZCY electrolyte without cracks. A-site doping in Fe-based layered perovskite cathodes promotes the single-cell output performance by around 100-26% at 550–700 °C, especially for the mixed-rare-earth doped PNBFZ with high peak power densities of 401–650 mW cm−2.

Hollow FeNi@NCG Materials Prepared with a Double-template Strategy as Highly Efficient Catalysts for Rechargeable Zn-air Batteries

One-step pyrolysis approach is the most common used method to synthesize the cathode catalysts of Zn-air batteries (ZABs). However, it is still a challenge to control the structural elements. Herein, a double-template strategy has been established by fabricating GO-doped porous g-C3N4 supported FeNi-MOF arrays as templates to synthesize the FeNi@NCG-T architecture as highly efficient electrocatalysts. The obtained FeNi@NCG-T catalysts exhibit well-defined hollow architecture with directional arrangement tendency, which may be advantageous to construct a tri-phase region so as to accelerate the O2-containing species transmission and increase the accessibility of internal active sites, thus boosting the catalytic performances and kinetics. The optimal Fe1Ni1@NCG-700 catalyst delivers excellent electrochemical activity with the overpotential of merely 217 mV (after iR correction) for OER (1 M KOH) and a remarkable small potential gap of 0.625 V between ORR and OER. The Fe1Ni1@NCG-700 based aqueous ZAB exhibits high peak power density of 210.79 mW·cm−2 and high specific capacity of 784.84 mAh·g−1 and long term charge/discharge stability. The corresponding button-shaped solid-state ZAB also presents excellent charge/discharge durability (>466 cycles) with outstanding performances. Most importantly, two as-synthesized button solid-state ZABs catalysts can afford a 2 V LED lamp over 36 h, proving the strong pratical application prospect.

High‐Performance Biomechanical Energy Harvester Enabled by Switching Interfacial Adhesion via Hydrogen Bonding and Phase Separation (Adv. Funct. Mater. 38/2022)

Biomechanical Energy Harvesters In article number 2204304, William W. Yu, Wen Jung Li, Walid A. Daoud, and co-workers demonstrate a high-performance flexible biomechanical energy harvester by switching its interfacial adhesion via hydrogen bonding interactions and solvent evaporation induced phase separation. This wearable power source can generate a record high peak power density of 20.5 W m−2 Hz−1 under a low biomechanical input of 5 N, and can sufficiently power small electronics through harvesting regular or intermittent human motions.

CoNi Nanoparticle-Decorated ZIF-67-Derived Hollow Carbon Cubes as a Bifunctional Electrocatalyst for Zn–Air Batteries

CoNi nanoparticle-decorated hollow carbon cubes (CoNi-HCCs) were synthesized using ZIF-67 as a sacrificial template. The synthesis utilizes the thermal instability of ZIF-67, creating hollow carbon nanostructures while facilitating carbonization and introducing metal nanoparticles (e.g., CoNi). Prototype Zn–air batteries equipped with CoNi-HCCs exhibited a promising discharge potential of 1.21 V and a charge potential of 2.04 V at 20 mA cm–2. These values are superior to those of Pt–Ru, whose discharge and charge potentials were 1.20 and 2.08 V, respectively. CoNi-HCCs also displayed a high peak power density of 159.6 mW cm–2, which is significantly higher than the value for Pt–Ru (120.2 mW cm–2). After 90 h of bifunctional cycling at 10 mA cm–2, CoNi-HCCs only experienced an efficiency loss of 3.4% and maintained 55.3% battery efficiency, much more durable than Pt–Ru (41.7% after only 60 h).

Highly Conductive and Durable Nb(Ta)-Doped Proton Conductors for Reversible Solid Oxide Cells

Proton-conducting reversible solid oxide cells (P-ReSOCs) are receiving increasing attention because they have potential to efficiently operate at intermediate temperatures to reduce cost and prolong operational life. Here we report our findings in the rational design of a new series of donor- and acceptor-codoped proton conductors through careful manipulation of defect chemistry. Specifically, BaNb(Ta)0.05Ce0.7Yb0.25O3-δ exhibits high ionic conductivity (0.012 S cm–1) while maintaining exceptional stability when exposed to Ar with 30% H2O at 500 °C for 500 h. In contrast, the resistance of BaZr0.1Ce0.7Y0.1Yb0.1O3-δ increases continuously with time under the same condition due to reaction with H2O, as rationalized using density functional theory (DFT)-based computations. In addition, single cells based on BaNb0.05Ce0.7Yb0.25O3-δ achieve a high peak power density of 1.12 W cm–2 in the fuel cell mode and a high current density of 2.24 A cm–2 at 1.3 V in the electrolysis mode at 600 °C. Overall, this work provides new insights for the development of highly conductive and stable proton conductors for P-ReSOCs.

MOF-Derived Co and Fe Species Loaded on N-Doped Carbon Networks as Efficient Oxygen Electrocatalysts for Zn-Air Batteries

HighlightsA novel method is developed to prepare bifunctional oxygen electrocatalysts composed of Co nanoparticles and highly dispersed Fe loaded on N-doped carbon substrates by virtues of metal-organic frameworks and two different doping processes.The designed catalysts show comparable performance with commercial catalysts. Meanwhile, rechargeable Zn-air batteries with prepared catalysts demonstrate high peak power density and good cycling stability.The performance promotion originates from the synergy between Co nanoparticles and highly dispersed Fe, porous structures, large specific areas, and distinct three-dimensional carbon networks. Searching for cheap, efficient, and stable oxygen electrocatalysts is vital to promote the practical performance of Zn-air batteries with high theoretic energy density. Herein, a series of Co nanoparticles and highly dispersed Fe loaded on N-doped porous carbon substrates are prepared through a “double-solvent” method with in situ doped metal-organic frameworks as precursors. The optimized catalysts exhibit excellent performance for oxygen reduction and evolution reaction. Furthermore, rechargeable Zn-air batteries with designed catalysts demonstrate higher peak power density and better cycling stability than those with commercial Pt/C+RuO2. According to structure characterizations and electrochemical tests, the interaction of Co nanoparticles and highly dispersed Fe contributes to the superior performance for oxygen electrocatalysis. In addition, large specific surface areas, porous structures and interconnected three-dimensional carbon networks also play important roles in improving oxygen electrocatalysis. This work provides inspiration for rational design of advanced oxygen electrocatalysts and paves a way for the practical application of rechargeable Zn-air batteries.

Thermal Migration Promotes the Formation of Manganese and Nitrogen Doped Polyhedral Surface for Boosted Oxygen Reduction Electrocatalysis.

Increasing the oxygen reduction reaction (ORR) catalytic activity of carbon-based electrocatalysts with robust stability is of great significance for their application. Herein, a feasible thermal migration strategy was proposed to construct manganese- and nitrogen-doped carbonaceous polyhedron frameworks coupled with manganese monoxide microrods (MnO-NC). Mn species were migrated to the surface of polyhedron frameworks, the shape of which was maintained at the high-temperature treatment. The Mn thermal migration not only created highly dispersed Mn-Nx active sites but also promoted graphitization, which benefited ORR electrocatalysis. Moreover, the MnO microrod-supported polyhedron frameworks provide beneficial mass transfer channels for electrocatalysis. Therefore, MnO-NC exhibited impressive ORR catalytic activity and stability in both alkaline and neutral electrolytes compared to commercial Pt/C catalysts. A magnesium-air battery (MAB) driven by MnO-NC delivered a high open circuit voltage and peak power density comparable to that driven by Pt/C. Notably, MnO-NC-driven MAB possessed a longer discharge time than the Pt/C-driven one, indicative of the superior catalytic performance of Mn-NC. This work provides a simple but effective strategy to construct carbonaceous framework electrocatalysts for boosted ORR, promoting the widespread application of metal-air batteries and fuel cells.

FeNi incorporated N doped carbon nanotubes from glucosamine hydrochloride as highly efficient bifunctional catalyst for long term rechargeable zinc-air batteries

The ingenious design and synthesis of low-cost, non-precious metal bifunctional catalysts for oxygen reduction reactions (ORR) and oxygen evolution reactions (OER) is a pressing demand to solve energy crisis and to promote the development of zinc-air batteries. Herein, a simple strategy was developed to derive FeNi incorporated N-doped carbon nanotube (denoted as glu-NiFe) from glucosamine. Extensive metal-nitrogen-carbon (M-N-C) and FeNi alloys act as electrocatalytic active sites for ORR and OER, respectively, together with highly graphitized carbon nanotubes for facilitating electron transport. And the combinations endow glu-NiFe with an ORR half-wave potential of 0.85 V and an OER potential of 1.67 V at 10 mA cm−2, which exceed commercial catalysts of Pt/C and RuO2. Furthermore, the rechargeable Zn-air battery based on glu-NiFe delivers a high peak power density of 127 mW cm−2 and superior cycling stability (over 240 h). Moreover, a favorable performance is exhibited by glu-NiFe based all solid-state Zn-air battery. This work will provide some assistance in designing efficient and low-cost bifunctional catalysts for high performance rechargeable Zn-air batteries.

Mn3+‐rich Manganese Phosphate Targeted for Enhanced Oxygen Reduction Reaction in Zinc‐Air Batteries

AbstractManganese phosphate‐based materials show great potential in the electrochemical energy field due to the structurally flexible phosphate framework stabilizing active sites. However, the insufficient number of active sites causes unsatisfactory activity. Herein, we prepare Mn3(PO4)2 ⋅ 3H2O nanosheets via simple liquid‐phase precipitation with hydrogen peroxide as an oxidant, which conduces to expose more Mn3+ active sites, thereby accelerating the four‐electron transfer pathway during oxygen reduction reaction. Accordingly, the optimal catalyst (MnPi‐1.0) possesses excellent catalytic performance with a half‐wave potential of 0.81 V and a diffusion‐limited current density of 5.38 mA cm−2 in contrast to the 0.73 V and 5.07 mA cm−2 of the pristine one, respectively. Furthermore, the zinc‐air battery based on MnPi‐1.0 delivers a high peak power density (132 mW cm−2) and outstanding spcific capacity(797 mAh gZn−1). This work provides a facile and feasible solution to tune the density of active sites of manganese phosphate‐based materials for favorable electrochemical performance.

Formation of hollow frameworks of dual-sided Fe/Fe3C@N-doped carbon nanotubes as bifunctional oxygen electrocatalyst for Zn-air batteries

Rational design of effective bifunctional inexpensive oxygen electrocatalyst is highly important for Zn-air batteries (ZABs), which can accelerate both oxygen reduction/evolution reactions at the oxygen electrode. Herein, we present the formation of hierarchical hollow frameworks of dual-sided Fe/Fe3C@N-doped carbon nanotubes (FNCHFs) through a template-engaged method. Benefitting from the synergistic effect between the robust hollow frameworks and in-situ grown dual-sided N-doped carbon nanotubes, the FNCHF electrocatalyst presents enhanced mass/electron transport with high structural stability. As a result, the FNCHFs based bifunctional oxygen electrode demonstrates a desirable oxygen electrocatalytic activity and stability with a half-wave potential of 0.863 V for oxygen reduction and an overpotential of 340 mV to reach the current density of 10 mA cm−2 for oxygen evolution. The corresponding ZAB exhibits a high peak power density of 206 mW cm−2, a high specific capacity of 781 mAh gZn−1, and a good cycling stability more than 300 h.

Imidazolium structural isomer pyrazolium: A better alkali-stable anion conductor for anion exchange membranes

Anion exchange membranes (AEMs) are a core component for energy conversion technologies such as fuel cells and water electrolyzers. Unfortunately, the functional cations in AEM often suffer from inferior durability in caustic media, especially at elevated temperatures or highly concentrated alkaline solutions. Therefore, the exploitation of novel cations that can endure highly alkaline environments while with synthetic feasibility and good ion conducting property is desired. Herein, a simple and easily available pyrazolium cation was evaluated and was alkaline stable in 5 M NaOH (aq) at 80 °C for at least 240 h, which is substantially stable than its structural isomer, imidazolium. The alkaline stability of pyrazolium was rationalized through analyses of the degradation energy barriers calculated by density functional theory. The excellent alkaline stability of pyrazolium cation encouraged the fabrication of AEMs functionalizing with pyrazolium head group anchored to poly(arylene alkylene) architecture. In contrast to imidazolium-based counterpart, pyrazolium cation enable the AEM with higher base stability, retaining ～80% of its initial conductivity after a 1000-h treatment in 1 M NaOH (aq) at 80 °C. Moreover, the AEM based on pyrazolium showed a high hydroxide ion conductivity up to 120 mS cm−1 at 80 °C and a high peak power density of 502 mW cm−2 after assembled into a H2–O2 fuel cell device.

High-performance H2O2 paper fuel cell boosted via electrolyte toning and radical generation

Cellulose paper has been employed to develop pumpless microfluidic fuel cells. Meanwhile, hydrogen peroxide as both the fuel and oxidant has attracted attention since it is eco-friendly for producing only water. However, low open-circuit voltage (OCV) and power density of reported H2O2 fuel cells due to the mixed potentials (simultaneous oxidation and reduction at the same electrode) preclude its applications. In this study, a H2O2 paper fuel cell with a gel-aided dual-electrolyte configuration has been proposed for the first time to solve this problem. An ion-conductive hydrogel has been sandwiched between the independent catholyte and anolyte flows to serve as part of the electrolyte. Its OCV has been elevated to 1 V and a high peak power density of 10.2 mW cm−2 has been achieved by toning the electrolytes, which exceeds most reported H2O2 fuel cells. The results demonstrate that alkaline anolyte benefits the cell performance more significantly than acidic catholyte does. The reaction mechanism at each electrode was further studied to provide insights for future development of H2O2 fuel cells: the reduction at the cathode follows the Fenton reaction; as for the oxidation at the anode, it was first revealed that H2O2 oxidation was facilitated by free radicals generated from H2O2 in alkaline media. Besides, the radicals also help to maintain a large voltage difference between the electrodes. Furthermore, this fuel cell shows great durability and can be instantly re-activated upon refueling. This gel-aided dual-electrolyte fuel cell design can pave a way for practical applications of direct H2O2 fuel cells.

Fe3C Decorated N, Fe Co‐Doped Hollow Carbon Microspheres as Efficient Air Electrode Catalyst for Zinc‐Air Battery

AbstractEfficient metal‐air batteries need active catalysts with low cost for both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Herein, hollow spherical Fe−M/G/H catalyst was synthesized through a polycondensation/pyrolysis method without template. Polycondensation of melamine, d‐glucose, and hexamethylenetetramine was accomplished to obtain carbon spheres with high nitrogen content. Hollow microspheres containing Fe‐Nx and Fe3C were fabricated by subsequent pyrolysis with Fe catalysts. Hollow microsphere structures not only expose more active sites (doped‐N, Fe‐Nx, and Fe3C), but also promote the mass transfer of O2. Fe−M/G/H possesses superior ORR performance in alkaline media with high limiting current density (5.09 mA cm−2) and half‐wave potential (0.80 V). The OER activity of Fe−M/G/H is superior to commercial Pt/C. Fe−M/G/H assembled zinc‐air battery exhibits high peak power density (90.27 mW cm−2) and long stability. This research provides a new approach to design hollow carbon catalysts with homo‐dispersed Fe‐Nx/Fe3C active sites and high doped‐N concentration.

MOF-Derived Fe-Zn-N-C Catalysts for Precious Metal Free Cathodes Showing High Performance in Anion-Exchange Membrane Fuel Cells

Hydrogen technologies such as low-temperature fuel cells are, besides batteries, the most promising technologies for mobility and transport applications. Currently, Proton Exchange Membrane Fuel Cells (PEMFCs) are, in terms of low-temperature fuel cells, the state-of-the-art technology achieving high power densities and reasonable stabilities. With the recent development and increasing availability of stable and performant hydroxide conductive ionomers, Anion Exchange Membrane Fuel Cells (AEMFCs) have gained increasing interest in recent years as they combine the advantages of PEMFCs, like low-temperature operation and high-power density with the low component costs of alkaline fuel cells.1,2 Especially the possibility of replacing the expensive Pt-based electrocatalysts used in PEMFCs with cheaper electrocatalysts like nickel-based materials for the anode and iron-based materials for the cathode could significantly decrease the fuel cell costs.1,3,4 Although the oxygen reduction reaction (ORR) at the cathode is favored in alkaline media compared to acidic media, the ORR is still a challenging reaction in AEMFCs.5,6 Over the last decades, various materials were investigated in order to replace the expensive Pt electrocatalysts at the cathode. Among these materials, iron- and nitrogen-doped carbons (Fe-N-C) with molecular iron sites (Fe-Nx) show comparable catalytic activities to Pt and decent stabilities.7–9 Fe-N-C catalysts can be obtained by co-pyrolysis of Fe- N-, and C-sources and subsequential acid leaching. One way to achieve Fe-N-C catalysts with high dispersion of Fe-Nx sites is by using Fe-doped metal-organic frameworks (Fe-MOFs) as precursors. These combine the presence of pre-coordinated Fe-Nx motives as well as high porosity and high specific surface area.10 To produce Fe-N-C catalysts, we synthesized Fe-, and Zn-doped MOFs (Fe-Zn-MOF) as multicomponent Fe-, Zn-, N-, and C-precursors and pyrolyzed them in the presence of additional nitrogen sources at high temperatures. The resulting Fe-Zn-N-C catalysts revealed high dispersion of Fe and Zn, high specific surface areas (400-600 m2/g), and high porosity as revealed by XRD, EDX, HAADF STEM, and N2 physisorption. Depending on the pre-treatment of the Fe-Zn-MOF, the Fe content of the resulting Fe-N-C catalyst could be varied. Benefiting from the high Fe-dispersion and the high specific surface areas, the best performing Fe-Zn-N-C catalyst with high Fe content shows high activity towards the ORR in alkaline media (0.1 mol/L KOH) as demonstrated by RDE measurements featuring a high half-wave potential (0.87 V vs. RHE) and high mass activity (47 mA/mgcat) and thereby outperforming a commercial 50 wt.% Pt/C catalyst in terms of half-wave potential (0.83 V vs. RHE).To investigate the performance of the Fe-Zn-N-C catalysts in AEMFCs, membrane electrode assemblies (MEAs) were prepared with the synthesized Fe-Zn-N-C catalysts at the cathode, a commercial PtRu/C catalyst (40 wt.% Pt, 20 wt.% Ru on carbon black, AlfaAesar) at the anode, and a commercial ionomer as membrane and catalyst layer ionomer. The AEMFC with the best performing Fe-Zn-N-C catalyst revealed a high peak power density of 850 mW/cm², which is among the highest reported peak power densities for non-precious metal cathode catalysts in combination with a commercially available anion exchange ionomer.1 D. R. Dekel, J. Power Sources, 2018, 375, 158–169.2 R. O’Hayre, S.-W. Cha, W. Colella and F. B. Prinz, Fuel Cell Fundamentals, John Wiley & Sons, Inc, Hoboken, NJ, USA, 2016.3 X. Ge, A. Sumboja, D. Wuu, T. An, B. Li, F. W. T. Goh, T. S. A. Hor, Y. Zong and Z. Liu, ACS Catal., 2015, 5, 4643–4667.4 E. S. Davydova, S. Mukerjee, F. Jaouen and D. R. Dekel, ACS Catal., 2018, 8, 6665–6690.5 M. Hren, M. Božič, D. Fakin, K. S. Kleinschek and S. Gorgieva, Sustain. Energy Fuels, 2021, 5, 604–637.6 N. Ramaswamy and S. Mukerjee, Adv. Phys. Chem., 2012, 2012, 1–17.7 X. Ren, B. Liu, X. Liang, Y. Wang, Q. Lv and A. Liu, J. Electrochem. Soc., 2021, 168, 044521.8 L. Osmieri, L. Pezzolato and S. Specchia, Curr. Opin. Electrochem., 2018, 9, 240–256.9 M. M. Hossen, K. Artyushkova, P. Atanassov and A. Serov, J. Power Sources, 2018, 375, 214–221.10 C. Li, D. H. Zhao, H. L. Long and M. Li, Rare Met., 2021, 40, 2657–2689.

Non-reactive HiPIMS deposition of NbCx thin films: Effect of the target power density on structure-mechanical properties

The exceptional mechanical properties of transition metal carbide coatings are known to be governed by the carbon content and its morphological distribution. Here, we verify the influence of the target peak power density on the chemical composition, microstructure, and mechanical properties of NbCx coatings grown by non-reactive high-power impulse magnetron sputtering (HiPIMS). By tuning the pulse parameters, the power density can be increased from 0.11 to 1.48 kW/cm2 leading to a decrease in the C/Nb ratio from 1.52 to 0.99 within the films – proven by combined elastic backscattering and time-of-flight elastic recoil detection analysis. This decrease in the C/Nb ratio is accompanied by microstructural changes from nanocomposite morphologies with an average grain size of 6.6 ± 2.5 nm at 0.13 kW/cm2 into more columnar structures with an average column width of 65.2 ± 18.7 nm at 1.48 kW/cm2. Independent from the C/Nb ratio, all films exhibit a single face-centered cubic structure. The mechanical properties correlate with the enhanced growth behavior dominated by ions at higher peak power densities and the varied C/Nb ratios. A maximum in hardness and fracture toughness of H = 38.7 ± 3.6 GPa and KIc = 2.78 ± 0.13 MPa∙m1/2 (at 3.2 GPa residual compressive stress), is obtained for the nearly stoichiometric NbC coating exhibiting C/Nb ratio of 1.06.

CoFeNi/N-codoped carbon nanotubes with small diameters derived from spherical Prussian blue analog as bifunctional oxygen electrocatalysts for rechargeable Zn-air batteries

Owing to sluggish kinetics of oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), it is still challenging to rationally design and construct bifunctional electrocatalysts with high performance, low-cost and good stability to substitute precious-metal catalysts. Herein, we introduce Ni ions to obtain spherical Prussian blue analog (PBA) doped with Co/Fe/Ni and further to synthesize nitrogen and Co/Fe/Ni co-doped carbon nanotubes (denoted as CoFeNi-CNTs) with small diameters (20–30 nm) by pyrolyzing the mixture of melamine and PBA. The optimized CoFeNi-CNTs have abundant metal-nitrogen-carbon (M-N-C) structures and CoFeNi nanoparticles respectively as effective ORR and OER active sites, which lead to outstanding electrocatalytic activities and durability with a half-wave potential of 0.85 V for ORR and an overpotential of 440 mV for OER. Especially, the rechargeable Zn-air battery based on CoFeNi-CNTs catalyst delivers a high peak power density of 138.7 mW cm -2 , specific capacity of 793 mAh g Zn -1 and stable charge-discharge cycling over 500 h, outperforming the Pt/C-RuO 2 based devices. And all-solid-state Zn-air battery also displays excellent discharge-charge performance and stability. This work explores the optimization of oxygen catalytic activity for carbon nanotubes by reducing diameters and constructing dual-active-sites strategy. • Co/Fe/Ni doped spherical Prussian blue analog (PBA) precursor is developed. • CoFeNi/N-doped carbon nanotubes (CoFeNi-CNTs) with small diameters are synthesized. • The CoFeNi-CNTs consist of Co/Fe/Ni-N-C and CoFeNi nanoparticle active sites. • The catalyst shows oxygen bifunctional catalytic activities with an overpotential of 820 mV. • The CoFeNi-CNTs based Zn-air batteries have high power density and durability.

Facile Approach to Enhance Activity and CO2 Resistance of a Novel Cobalt-Free Perovskite Cathode for Solid Oxide Fuel Cells.

Developing high-performance and cost-effective cathodes is ever-increasingly vital for the advancement of intermediate-temperature solid oxide fuel cells (IT-SOFCs). To facilitate the popularization of nonprecious metallic and cobalt-free oxygen reduction electrodes, herein, we propose a novel perovskite-based BaFeO3-δ (BF) matrix, Ba0.75Sr0.25Fe0.875Y0.125O3-δ (BSFY), as a highly active cathode for IT-SOFCs. To our satisfaction, the BSFY electrode showcases a low area-specific resistance of 0.063 Ω cm2, as well as a high peak power density of 1288 mW cm-2 at 600 °C, yielding a more than threefold improvement compared to that of its BF counterpart (371 mW cm-2). The long-term durability test highlights its practicability under the IT operating condition. When tested in 10 vol % CO2-containing air, the BSFY electrode exhibits impressive resistance against contaminants within 50 h (<0.4 Ω cm2 with a deterioration rate of ∼0.00011 Ω cm2 min-1). Coupled with its reversible response between pure air and the contaminant, the BSFY cathode is expected to be a promising cobalt-free alternative with high CO2 resistance for IT-SOFCs.

Perovskite-Carbon Joint Substrate for Practical Application in Proton Exchange Membrane Fuel Cells under Low-Humidity/High-Temperature Conditions.

Highly active catalysts with promising water retention are favorable for proton exchange membrane fuel cells (PEMFCs) operating under low-humidity/high-temperature conditions. When PEMFCs operate under low-humidity/high-temperature conditions, performance attenuation rapidly occurs owing to reduced proton conductivity of dehydrated membrane electrode assemblies. Herein, we load platinum onto a perovskite-carbon joint substrate (BaZr0.1Ce0.7Y0.1Yb0.1O3-σ-XC-72R) to construct a highly active and durable catalyst with good water retention capacity. We propose that the Pt/(BZCYYb-C) catalyst layer at cathode can promote the water back diffusion of produced water from the cathode to the membrane, thus preventing the decay of fuel-cell performance under low-humidity/high-temperature conditions. The catalyst exhibited outstanding mass activity of 0.542 A mgpt-1 at 0.9 V vs RHE. PEMFCs with such a catalyst delivered very high peak power densities (1.70/1.14 W cm-2 under H2-O2/air conditions at 70 °C) and kept 85.3%/92.1% of initial performance values under low-humidity/high-temperature conditions (relative humidity 60%@70 °C/100 °C).

Bifunctional electrocatalyst with CoN3 active sties dispersed on N-doped graphitic carbon nanosheets for ultrastable Zn-air batteries

Realizing large-scale production of low-cost bifunctional catalysts is pivotal to promoting the practical application of Zn-air batteries. Herein, we successfully constructed unique bifunctional CoN3 catalytic sites atomically dispersed on N-doped graphitic carbon nanosheets (CoSA/NCs), which enable Zn-air batteries with ultrahigh durability for over 6000 cycles (~ 2000 h). The 2D carbon construction and single-atom Co formation were achieved simultaneously in salt-assisted process employing CoCl2. CoCl2 serves as a recyclable template, a pore-making agent, and a catalyst for graphitization, which effectively enables the catalyst with abundant active sites catalyze ORR and OER. Our experimental and theoretical modeling results confirm that of CoN3 surpasses CoN4 in term of the ORR and OER catalytic activity. The Zn-air battery based on CoSA/NCs catalyst exhibits a high peak power density of 255 mW cm−2. With unparalleled catalytic performance and low production cost, this catalyst paves the way for the potential large-scale application of Zn-air batteries.