Application Of Metal-air Batteries Research Articles

Enhanced Electrocatalytic Stability of Platinum Nanoparticles Supported on Sulfur-Doped Carbon using in-situ Solution Plasma

The metal-air battery is a form of renewable energy generation technology that produces energy electrochemically and can address energy concerns in the near future. However, state-of-the-art Pt electrocatalysts often suffer from agglomeration or detachment from carbon supports under prolonged operation, eventually limiting the long-term utilization of metal-air batteries. In this work, Pt nanoparticles were deposited on sulfur-doped nanocarbon to increase its stability. We first synthesized sulfur-doped (S-doped) and pristine carbon as support materials via a plasma process, and thereafter loaded platinum (Pt) nanoparticles onto the S-doped and pristine carbon matrix. From a sintering test at 600 °C, the Pt nanoparticles supported on pristine carbon increased from 2.4 to 5.2 nm; meanwhile, the average size of Pt NPs supported on S-doped carbon only increased from 2.2 to 2.51 nm. From the electrochemical analyses, the mass activity of Pt on pristine and S-doped carbon supports decreased by 25% and 10%, respectively, after 1500 cycles. The results proposed that the sulfide C–S–C bond provided a strong platinum-S-doped carbon support interaction between the support materials and the loaded Pt nanoparticles. Thus, S-doped carbon supports can serve as a stabilizer of Pt nanoparticles to enhance their durability in the application of metal-air batteries and other electrochemical devices.

Co3O4 Nanocube -3DrGO Hybrid Structure: Efficient Non-Noble-Metal Electrocatalyst with High-Performance for Oxygen Evolution Reaction

Oxygen Evolution reaction (OER) by water splitting is one of the emerging technologies for the ongoing research in the field of sustainable, clean yet highly efficient energy generation. Electrocatalysis for OER is a key step forward towards achieving this goal and enormous efforts has been devoted recently on the development of high-performance electrocatalysts that are cost-effective, abundant as well as environmentally benign. Transition metal based non-noble electrocatalysts anchored on high-surface area, conductive carbonaceous support serves the dual purpose of being highly catalytically active as well as having excellent stability. Herein, we report the synthesis of Co3O4 nanocube -3DrGO hybrid structure as a high-performance electrocatalyst for OER applications via a facile hydrothermal synthesis technique followed by heat treatment. The unique nanocube like structure offers more active edge sites which plays an important role in its catalytic performance. The hybrid structure exhibits an overpotential of 428 mV (vs RHE) and a small tafel slope of 96.92 mV dec-1 with 100% faradaic efficiency in 1 M NaOH alkaline electrolyte. The electrode needs an overpotential of 648 mV to afford a current density of 10 mA cm-2. This offers a low-cost electrocatalytic electrode for water splitting and rechargeable metal–air battery applications. Figure 1

Modeling of Si-B-N Sheets and Derivatives as a Potential Sorbent Material for the Adsorption of Li+ Ion and CO2 Gas Molecule.

In the present exploration, a few Si–B–N derivatives are derived to adsorb Li ions and CO2 gas molecules for the potential application of metal–air batteries. The newly derived structure’s bond lengths are as follows: Si=Si, 2.2 Å; Si–B, 1.9 Å; Si–N, 1.7 Å; and B–N, 1.4 Å, consistent with the experimental results of relevant structures. The stability of the newly derived structures is examined by the atom-centered density propagation study by varying the temperature from 270 to 400 K, and no structural variations are observed throughout the dynamics. Li adsorption on the Si4B2 ring has the maximum binding energy of −3.9 eV, and the result is consistent with the previous results. The rings with the 2:1 silicon–boron ratio provide strong adsorption for Li atoms. The calculated maximum electromotive force of the newly derived sheets is 0.56 V with the maximum theoretical density of 783 Wh/kg. Similarly, the maximum adsorption of CO2 on the sheet is −0.106 eV, which is considerably higher than that on graphene and its derivatives. CO2 adsorption has been carried out in the presence of water molecules to investigate the change in CO2 adsorption with the moisture (water) content, and the results show no significant change in the adsorption of CO2 with moisture. However, water has a strong interaction with the maximum interaction energy of −0.72 eV. Further, to explore the potential ability of the sheets, each sheet’s edges are examined as hydrogen storage expedient and the surface as an artificial photosynthesis platform. The Si4B2 ring is more favorable for the adsorption of H atom with the chemisorption of −7.138 eV. Similarly, all of the major UV-absorption spectral peaks fall between 450 and 800 nm, which shows that the sheet can be used as an artificial photosynthesis platform.

Iron-Salt Thermally Emitted Strategy to Prepare Graphene-like Carbon Nanosheets with Trapped Fe Species for an Efficient Electrocatalytic Oxygen Reduction Reaction in the All-pH Range.

Earth-abundant, highly active, and durable electrocatalysts toward oxygen reduction reaction (ORR) in the all-pH range are highly required for practical application of electrochemical energy conversion technologies. Here, non-noble-metal graphene-like carbon nanosheets with trapped Fe species (Fe-N/GPC) are developed by an iron-salt thermally emitted strategy, which integrates the modulation of the electronic structure for boosted intrinsic activity with the engineering of hierarchical porosity for enriched active sites. The ORR electrocatalytic performance of Fe-N/GPC-800 achieves the half-wave potentials of 0.86 and 0.77 V with limiting current densities of 6.1 and 4.7 mA cm-2 in 0.1 M KOH and 0.1 M PBS solutions, respectively, as well as respectable stability. Furthermore, Fe-N/GPC-800 also shows considerable ORR catalytic activity in acid media accompanied by stability superior to those of Pt/C catalysts. The as-prepared Fe-N/GPC-800, as a cathodic catalyst, is assessed in a Zn-air battery test and delivers an open-circuit voltage of 1.44 V with a power density of 134 mW cm-2 as well as the outstanding durability after 350 cycles at 10 mA cm-2, demonstrating appreciable promise in application of metal-air batteries. This work provides an enabling and versatile strategy for facile and scale-up preparation of high-performance non-noble-metal electrocatalysts.

Nitrogen/sulfur dual-doped porous carbon nanofibers with Co9S8 nanoparticles encapsulated by graphitic shells: A highly active stable free-standing air electrode for rechargeable non-aqueous Li-O2 batteries and primary alkaline Al-air batteries

The rational design of economical air cathodes or electrocatalysts with high electrocatalytic activity and durability for both non-aqueous lithium-oxygen (Li-O2) and alkaline electrolyte aluminum-air (Al-air) batteries is a critical factor for promoting the practical applications. Herein, we report the fabrication of graphitic layers covered with Co9S8 nanoparticles immobilized inside N,S dual-doped hierarchical porous carbon nanofibers by a facile and one-step electrospinning method combined with a pyrolytic process. When employed as free-standing electrodes for a Li-O2 battery and an Al-air battery, the as-prepared Co9S8@G/NS-PCNFs deliver excellent battery performances and afford comparable catalytic performance as that of a 20 wt% Pt/C electrode. The results show that the superior battery performance of the Co9S8@G/NS-PCNF cathode can be attributed to the synergistic effect between the catalytic behavior of the uniformly distributed Co9S8 nanoparticles and the textural properties of the N,S dual-doped hierarchical porous carbon nanofibers. Our findings open a new direction for designing nonprecious hybrid metal sulfide carbon architectures to replace costly Pt/C electrodes and indicate their promising application in next-generation metal-air batteries.

Enhanced Bifunctional Catalytic Activity of Manganese Oxide/Perovskite Hierarchical Core-Shell Materials by Adjusting the Interface for Metal-Air Batteries.

LaMnO3 perovskite is one of the most promising catalysts for oxygen reduction reaction (ORR) in metal-air batteries and can be compared to Pt/C. However, the low catalytic activity toward oxygen evolution reaction (OER) limits its practical application in rechargeable metal-air batteries. In this work, the MnO2/La0.7Sr0.3MnO3 hierarchical core-shell composite materials with a special interface structure have been designed via the selective dissolution method. The core of La0.7Sr0.3MnO3 particles is wrapped by the porous and loose MnO2 nanoparticles. The as-prepared MnO2/La0.7Sr0.3MnO3 materials have excellent catalytic activity toward ORR/OER and are used as bifunctional oxygen electrocatalysts for metal-air batteries. Based on results of transmission electron microscopy, X-ray photoelectron spectroscopy, valence-band spectroscopy, and O2 temperature-programmed desorption analysis, we conclude that the bifunctional catalytic activity of the MnO2/La0.7Sr0.3MnO3 materials can be effectively promoted due to the specific interface structure between the La1-xSrxMnO3 core and the MnO2 shell. This can be attributed to three aspects: (a) the electronic conductivity, which is beneficial for providing the faster charge-transfer paths and kinetics at the oxide/solution interface than that of the MnO2 sample; (b) the enhancement of oxygen adsorption capacity due to surface defects (oxygen vacancies) and chemical adsorption, which is helpful to improve the reaction kinetics during the process of oxygen catalysis; and (c) the tuning of oxygen adsorption ability via the moderate Mn-O bond strength, which may be conducive to getting for obtain an enhanced Mn-O bond strength on the surfaces for ORR and a weakened Mn-O bond in the lattice for OER.

Facile synthesis of ternary spinel Co–Mn–Ni nanorods as efficient bi-functional oxygen catalysts for rechargeable zinc-air batteries

Facile synthesis of high efficient bi-functional oxygen catalysts is important for large-scale application of rechargeable metal-air batteries. Herein, an ethanol-water mediated co-precipitation approach is applied to fabricate Co–Mn–Ni (CMN) ternary spinel oxides with uniform 1D structure. Their catalytic activities toward the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are investigated by the rotating ring-disk electrode (RRDE) techniques. The ternary spinel oxide with the Co/Mn/Ni atomic ratio of 2:3:1 (CMN-231) exhibits the best bi-functional activities among the as-prepared ternary, binary and unitary spinel oxides (△E is as low as 0.88 V), which can be attributed to its reasonable element composition, mesoporous nanorod structure, strong oxygen-adsorption ability and good charger-transfer capability. In addition, the CMN-231 catalyst demonstrates a strong stability during long-term operation. This well-designed catalyst is applied in a homemade zinc-air battery, and exhibits good charge–discharge performances (voltage gap is 0.9 V at 50 mA cm−2) and remarkable cycling stability.

Development of micro-tubular perovskite cathode catalyst with bi-functionality on ORR/OER for metal-air battery applications

Development of micro-tubular perovskite cathode catalyst with bi-functionality on ORR/OER for metal-air battery applications

Atomic scandium and nitrogen-codoped graphene for oxygen reduction reaction

Rational design of highly active and durable electrocatalysts for oxygen reduction reaction is critical to substitute precious metal platinum for fuel cells. Herein, a novel non-precious atomic scandium embedded into nitrogen-doped graphene material is successfully synthesized via a facile annealing method. The catalyst exhibits superior oxygen reduction reaction performance in both 0.1 M KOH and 0.5 M H2SO4, with onset potential (Eonset, 0.99 vs 0.82 V) and half-wave potential (E1/2, 0.89 vs 0.72 V). Theoretical calculations reveal that the possible active sites for ORR might be ScN3O and ScN2O embedded into the N-doped graphene. The outstanding electrochemical stability and strong tolerance to methanol crossover on the atomic scandium and nitrogen-codoped graphene make it a promising application in metal-air batteries and fuel cells.

"Ship in a Bottle" Design of Highly Efficient Bifunctional Electrocatalysts for Long-Lasting Rechargeable Zn-Air Batteries.

The poor durability of bifunctional oxygen electrocatalysts is one main bottleneck that suppresses the widespread application of rechargeable metal-air batteries. Herein, a "ship in a bottle" design is achieved by impregnating fine transition metal dichalcogenide nanoparticles into defective carbon pores that act as interconnected nanoreactors. The erected 3D porous conductive architecture provides a "highway" for expediting charge and mass transfer. This design not only delivers a high surface-to-volume ratio to increase numbers of exposed catalytic sites but also precludes nanoparticles from aggregation during cycling owing to the pore spatial confinement effect. Therefore, the long-term plague inherent to nanocatalyst stability can be solved. Moreover, the synergistic coupling effects between defect-rich interfaces and chemical bonding derived from heteroatom-doping boost the catalytic activity and prohibit the detachment of nanoparticles for better stability. Consequently, the developed catalyst presents superior bifunctional oxygen electrocatalytic activities and durability, out-performing the best-known noble-metal benchmarks. In a practical application to rechargeable Zn-air batteries, long-term cyclability for over 340 h is realized at a high current density of 25 mA cm-2 in ambient air while retaining an intact structure. Such a universal "ship in a bottle" design offers an appealing and instructive model of nanomaterial engineering for implementation in various fields.

Carbon-coated MnCo2O4 nanowire as bifunctional oxygen catalysts for rechargeable Zn-air batteries

The catalytic activity of spinel-type MnCo2O4 is often limited by the poor electronic conductivity, limited specific surface area and inferior stability in oxygen reduction reaction and oxygen evolution reaction. In this study, carbon-coated MnCo2O4 nanowire (MnCo2O4@C) is prepared by a self-template method from MnCo2-NTA nanowire precursor. MnCo2O4@C shows excellent electrocatalytic performance and improved circulation stability, with an onset potential of 0.92 V and current retention rate of 99% within 10000 s at 0.80 V vs. RHE, better than the commercial Pt/C (Eonset = 0.94 V, current retention rate 94%). Further study shows that the oxygen reduction mechanism of MnCo2O4@C follows quasi-four-electron transfer process. The carbon provides conductive network and promotes the fast transfer of electrons in between the carbon network and MnCo2O4 nanoparticles. Meanwhile, under the limitation of rigid carbon shell, the growth of MnCo2O4 nanoparticle is impeded. These make MnCo2O4@C excellent electrochemical properties, and endow rechargeable Zn-air battery with high open-circuit voltage of 1.43 V and long-term cycling performance over 70 h with high efficiency and stability. MnCo2O4@C holds great promise as highly active bifunctional electrocatalyst in the practical application of rechargeable metal-air batteries and other fuel cells.

Mass-loading independent electrocatalyst with high performance for oxygen reduction reaction and Zn-air battery based on Co-N-codoped carbon nanotube assembled microspheres

Although carbon materials have shown large potential as efficient electrocatalysts for oxygen reduction reaction (ORR), their practical performance with high energy density and power density is difficult to maintain under high mass-loading due to the compact restacking that seriously hinders mass/charge diffusion. To overcome this issue, we demonstrate the design and synthesis of hierarchical Co-N-codoped carbon nanotube hollow microspheres (CNT HMSs) with high disperse, large surface area and uniform mesopores, which effectively guarantees the high electrochemical activity and stability towards ORR even under high mass-loading. As a result, the power density of Zn-air battery based on CNT HMS gradually enhances from 52.8 to 183.8 mW cm−2 with a good linear relationship when the mass-loading increases from 1.5 (traditional used for most reported works) to 6.0 mg cm−2, indicating a well-preserved catalytic activity with high mass-loading. In addition, the long-term stability (10 h) test illustrates that monodisperse morphology and uniform size distribution of CNT HMS have been well maintained, while the referent carbon particles show serious agglomeration and obvious increased particle size. This suggests a much enhanced stability of CNT HMS compared with traditional particles, which offers large opportunity for the practical applications in metal-air batteries or fuel cells.

La0.8Sr0.2MnO3 based perovskite with A-site deficiencies as high performance bifunctional electrocatalyst for oxygen reduction and evolution reaction in alkaline

In this work, the A-site cation deficient perovskites (La0.8Sr0.2)1-xMnO3(x=0, 0.02, 0.05)(LSM) and Fe doped perovskite (La0.8Sr0.2)0.95Mn0.5Fe0.5O3(LSMF) are prepared by sol-gel process assisted with chelating effect of citric acid. The structure, morphology and valence state of the prepared samples were characterized. Their catalytic activities toward oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) were investigated by rotating-disk electrode (RDE). As expected, appropriate introduce of A-site deficiency can enhance both ORR and OER activities. Among the A-site cation deficient perovskites studied, (La0.8Sr0.2)0.95MnO3 exhibited the highest ORR and OER activities and, hence, the best bifunctionality. After doping with Fe in the B-site, the (La0.8Sr0.2)0.95Mn0.5Fe0.5O3 perovskite exhibits even better electrochemical catalytic activity which is due to the increase of the concentration of oxygen vacancy as compared with (La0.8Sr0.2)0.95MnO3. Furthermore, (La0.8Sr0.2)0.95Mn0.5Fe0.5O3 showed superior durability than commercial 20wt% Pt/C catalyst. This work indicates that introduce of A-site deficiency and B-site Fe doping in perovskite oxides is an effective strategy to enhance ORR and OER activity for the applications in metal-air batteries.

MnO/N-Doped Mesoporous Carbon as Advanced Oxygen Reduction Reaction Electrocatalyst for Zinc-Air Batteries.

The development of alternative electrocatalysts exhibiting high activity in the oxygen reduction reaction (ORR) is vital for the deployment of large-scale clean energy devices, such as fuel cells and zinc-air batteries. N-doped carbon materials offer a promising platform for the design and synthesis of electrocatalysts due to their high ORR activity, high surface area, and tunable porosity. In this study, materials in which MnO nanoparticles are entrapped in N-doped mesoporous carbon (MnO/NC) were developed as electrocatalysts for the ORR, and their performances were evaluated in zinc-air batteries. The obtained carbon materials had large surface area and high electrocatalytic activity toward the ORR. The carbon compounds were fabricated by using NaCl as template in a one-pot process, which significantly simplifies the procedure for preparing mesoporous carbon materials and in turn reduces the total cost. A primary zinc-air battery based on this material exhibits an open-circuit voltage of 1.49 V, which is higher than that of conventional zinc-air batteries with Pt/C (Pt/C cell) as ORR catalyst (1.41 V). The assembled zinc-air battery delivered a peak power density of 168 mW cm-2 at a current density of about 200 mA cm-2 , which is higher than that of an equivalent Pt/C cell (151 mW cm-2 at a current density of ca. 200 mA cm-2 ). The electrocatalytic data revealed that MnO/NC is a promising nonprecious-metal ORR catalyst for practical applications in metal-air batteries.

Cobalt metalloid and polybenzoxazine derived composites for bifunctional oxygen electrocatalysis

The development of bifunctional oxygen electrodes is a key factor for the envisaged application of rechargeable metal-air batteries. In this work, we present a simple procedure based on pyrolysis of polybenzoxazine/metal metalloid nanoparticles composites into efficient bifunctional oxygen reduction and oxygen evolution electrocatalysts. This procedure generates nitrogen-doped carbon with embedded metal metalloid nanoparticles exhibiting high activity towards both, oxygen reduction and oxygen evolution, in 0.1 M KOH with a roundtrip voltage of as low as 0.81 V. Koutecký-Levich analysis coupled with scanning electrochemical microscopy reveals that oxygen is preferentially reduced in a 4e− transfer pathway to hydroxide rather than to hydrogen peroxide. Furthermore, the polybenzoxazine derived carbon matrix allows for stable catalyst fixation on the electrode surface, resulting in unattenuated activity during continuous alternate polarisation between oxygen evolution at 10 mA cm−2 and oxygen reduction at −1.0 mA cm−2.

Zn3[Fe(CN)6]2 derived Fe/Fe5C2@N-doped carbon as a highly effective oxygen reduction reaction catalyst for zinc-air battery

We fabricated a highly effective oxygen reduction reaction (ORR) catalyst consisting of Fe/Fe5C2 species wrapped in N-doped carbon (Fe/Fe5C2@N-C), derived from annealing decomposition of a zinciferous Prussian blue analogue Zn3[Fe(CN)6]2, which can be prepared through a facile precipitation reaction. The rationally designed carbon layer-encapsulated structure with iron/iron carbide encased inside the N-doped graphitic carbon shells is favorable for ORR, wherein the iron species not only facilitate the graphitization process but also improve the ORR activity together with outside N-doped graphic carbon. The resultant catalyst demonstrates a positive half-wave potential (E1/2) of 0.85 V (vs. RHE) and a nearly four-electron pathway in 0.1 M KOH solution, comparable to that of the commercial Pt/C. With superior stability to that of Pt/C, Fe/Fe5C2@N-C suffers almost no performance attenuation after 5000 potential cycles. The zinc-air battery using Fe/Fe5C2@N-C catalyst exhibits high power density and capacity, holding great promise for the practical application of metal-air batteries.

Cobalt porphyrin supported on graphene/Ni (111) surface: Enhanced oxygen evolution/reduction reaction and the role of electron coupling

Metal porphyrins have received sustained attention due to their remarkable catalytic properties. However, the catalytic activities of porphyrins are still moderate for oxygen reduction /evolution (ORR/OER) due to the high binding energies between the catalyst and reactant. Herein, we propose a novel strategy to modulate the binding energies of the oxygenated intermediates by introducing electron coupling between the substrate and the metal porphyrin. Our results reveal remarkable enhancement of OER/ORR performance when the Co-porphyrin molecule is supported on the graphene/Ni (111) substrate. The ORR/OER overpotentials can be greatly reduced, in particular for ORR from 0.6 V to 0.31 V. The enhanced ORR/OER activity of Co-porphyrin/graphene/Ni system stems from the electronic coupling between the catalyst and the substrate that modulates the binding strength between catalytic active sites and the reaction intermediates. Our study represents an efficient strategy to design low-cost, high performance, bifunctional electrocatalysts for the application in rechargeable metal-air batteries.

A metal-organic framework-derived bifunctional catalyst for hybrid sodium-air batteries

Metal-organic framework (MOF)-derived carbon nanomaterials are investigated as promising non-noble metal-based oxygen electrocatalysts for metal-air batteries. Herein, metal-organic framework-derived N-doped carbon nanotubes (MOF-NCNTs) were first employed as electrocatalysts for hybrid sodium-air batteries (SABs), which exhibited higher electrocatalytic activity and stability for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) compared to commercial Pt/C. The battery using MOF-NCNTs displayed the voltage gap of 0.30 V at a current density of 0.1 mA·cm―2, which is the lowest among all the tested catalysts including commercial Pt/C (0.50 V), RuO2 (0.50 V), Co-CNTs (0.67 V), NCNTs (0.77 V), MWNTs (0.90 V), and carbon paper (1.18 V). In addition, the average discharge plateau and round trip efficiency of the battery was 2.81 V and 87% during 35 cycles at a current density of 0.1 mA·cm―2, respectively. The remarkable electrocatalytic activity is mainly ascribed to the synergistic effect between the N dopants and confined Co nanoparticles in the CNTs, the hollow structure of NCNTs, and the robust porous cage structure. The N dopants and confined Co nanoparticles in the CNTs induce more catalytic active sites and promote electron transfer for the ORR and OER. The hollow framework structure of NCNTs not only offer structural defect sites for O2 adsorption, but also improves mass transport and electronic conductivity, resulting in enhanced catalytic activity. The robust porous cage structure contributes to the stability of the catalysts. The highly efficient and inexpensive metal-organic framework-derived NCNT is a promising bifunctional oxygen electrocatalyst for practical applications in hybrid SABs and other metal-air batteries.

Modeling of 2-D hydrogen-edge capped defected & boron-doped defected graphene sheets for the adsorption of CO2, SO2 towards energy harvesting applications

The metal-air batteries are potentially promising energy storage system that attracts due to their high theoretical energy density among other electrochemical energy storage systems. To infiltrate new barriers in the metal-air battery technology, air electrodes and its adsorption mechanisms are pre-eminent to understand the adsorption process at the atomic level. Graphene and its defects are proven as a better air electrode in the metal-air battery technology for the past few decades. Graphene can be tunable, superior compatibility with its defects and dopants, those make graphene as a potentially unique and important material to investigate. In our present study, we investigate 5-8-5, 55-77 (Stone-Waals), 555-777 and 5555-6-7777 defected sheets by functionalizing them with hydrogen around the edges and doping each defect by replacing a carbon atom with boron atom. This density functional study provides the better adsorption mechanism of CO2 and SO2 gas molecules on the defected and boron doped graphene sheets in favour of metal-air battery applications. We found that modeled sheets are favourable for the adsorption of the SO2 gas molecule with the maximum adsorption energy of −0.343 eV, induced by 555-777 defected graphene sheet. After adsorption, it can provide proficient catalyst reactions by expanding the SO bond length to 1.460 Å. Further, we have examined the di-vacancy defects as a hydrogen storage tool and artificial photosynthesis platform. The edges are highly reactive and have shown strong binding energy with hydrogen atom. Similarly, CO2 adsorbed UV absorption graph in sheets exhibit hypsochromic effect other than 5-8-5 and B-555-777 sheets, whereas 5-8-5 and B-555-777 sheets exhibit bathochromic effect and the absorption graphs are fallen in between visible regions, which are good for photosynthesis.

Nanocomposites CoPt-x/Diatomite-C as oxygen reversible electrocatalysts for zinc-air batteries: Diatomite boosted the catalytic activity and durability

The exploration of oxygen reversible electrocatalysts to boost oxygen reduction reaction and oxygen evolution reaction is critical for the development of high-performance aqueous Zn-air batteries. Since diatomite with porous structure can adsorb metal ions in aqueous solution, herein, we prepare the nanocomposite CoPt-x/Diatomite-C for both oxygen reduction and evolution reactions, and diatomite is found significantly promotes the electrocatalytic activity and durability. With the presence of diatomite, CoPt-1/Diatomite-C shows a lower Tafel slope (63 mV dec−1 at high potential range), larger diffusion-limited current density (4.94 mA cm−2) and superior durability for ORR. Particularly, the specific and mass activities of CoPt-1/Diatomite-C for ORR are 0.74 mA cm−2 and 286 mA mg−1, respectively, which are 2.5 and 3.0 times higher than that of CoPt-1/C without diatomite; For OER, the overpotential of CoPt-9/Diatomite-C decreases nearly 30 mV at 10 mA cm−2, while the Tafel slope also reduces 16 mV dec−1 versus CoPt-9/C catalyst. Moreover, a rechargeable Zn-air battery with these composites as air-cathode is self-assembled, and diatomite boosts the battery performance with desirable properties. CoPt-9/Diatomite-C displays the optimal performance, with a power density of 140 mW cm−2, a specific capacity of 616 mA h g−1 at 10 mA cm−2 and an exceedingly robust cycling life. This work provides a viable and cost-effective strategy for fabricating oxygen reversible electrocatalysts for metal-air battery applications.