Coordination polymer-induced interface engineering for high-density dual-Fe oxygen reduction catalysts in Zn–Air batteries

Incorporating intermittent renewable energy sources into the power grid will require large amounts of grid-scale energy storage. Electrochemical batteries are a versatile and scalable energy storage option and, hence, Li-ion batteries have been widely adopted to store excess wind and solar energy [1]. Li-ion batteries, however, have a relatively low energy density and serious safety concerns. An alternative electrochemical battery option lies with zinc-air batteries. This technology uses lower cost materials and is overall much safer. Furthermore, zinc-air batteries have a much larger theoretical energy density than Li-ion batteries [2]. The major impediment to wide-scale adoption of zinc-air batteries is the low energy efficiency because of the poor reaction kinetics at the air electrode. Both the charge and discharge reactions at the air electrode are sluggish and require the use of catalysts to obtain practicable performance. However, many catalysts active towards the charge reaction are not active towards the discharge reaction, and vice versa. The development of a catalyst active towards both the charge and discharge reactions, known as a bifunctional catalyst, is therefore a high priority [3]. Furthermore, catalysts employed in zinc-air batteries often show instability, with performance degradation evident after a few cycles. Ultimately, a highly stable bifunctional zinc-air battery catalyst is of the utmost importance.The aim of this work is to develop highly stable bifunctional catalysts for zinc-air batteries using atomic layer deposition (ALD). With ALD, extremely conformal catalyst coatings can be deposited directly on the air electrode of a zinc-air battery. The self-limiting surface reactions of ALD ensure that electrode porosity is maintained while maximizing the total coating surface area [4]. Since ALD operates in the gas phase, catalytic coatings can be deposited deep within the pores of the air electrode. This will help maintain the three-phase boundary necessary for the discharge reaction and ultimately improve the stability of a zinc-air battery [5]. To create a bifunctional catalyst, two ALD processes, one for manganese oxide and another for iron oxide, is combined into one ALD supercycle, depositing a mixed manganese-iron oxide. Since manganese oxide is a well-established discharge catalyst [6], and iron oxide demonstrates activity towards the charge reaction [7], this mixed manganese-iron oxide exhibits bifunctional activity in a zinc-air battery. An optimized supercycle process will be discussed and full-cell battery test results showcased. Specifically, the bifunctional efficiency of a zinc-air battery can be improved by more than 10% by using the mixed manganese-iron oxide catalyst. In addition, the high stability of the manganese-iron oxide catalyst is demonstrated, where bifunctional efficiency can be maintained at over 95% of the initial value over 200 cycles. Materials characterization of the mixed manganese-iron oxide, deposited through ALD, is also included.[1] L. Trahey, F. R. Brushett, N. P. Balsara, G. Ceder, L. Cheng, Y. M. Chiang, N. T. Hahn, B. J. Ingram, S. D. Minteer, J. S. Moore, K. T. Mueller, L. F. Nazar, K. A. Persson, D. J. Siegel, K. Xu, K. R. Zavadil, V. Srinivasan, and G. W. Crabtree, “Energy Storage Emerging: A Perspective from the Joint Center for Energy Storage Research,” Proc. Natl. Acad. Sci. U. S. A., vol. 117, no. 23, pp. 12550–12557, 2020.[2] J. Fu, R. Liang, G. Liu, A. Yu, Z. Bai, L. Yang, and Z. Chen, “Recent Progress in Electrically Rechargeable Zinc – Air Batteries,” Adv. Mater., vol. 31, no. 31, p. 1805230, 2019.[3] E. Davari and D. G. Ivey, “Bifunctional electrocatalysts for Zn – air batteries,” Sustain. Energy Fuels, vol. 2, no. 1, pp. 39–67, 2018.[4] C. Detavernier, J. Dendooven, S. Pulinthanathu Sree, K. F. Ludwig, and J. A. Martens, “Tailoring nanoporous materials by atomic layer deposition,” Chem. Soc. Rev., vol. 40, no. 11, pp. 5242–5253, 2011.[5] M. P. Clark, M. Xiong, K. Cadien, and D. G. Ivey, “High Performance Oxygen Reduction/Evolution Electrodes for Zinc − Air Batteries Prepared by Atomic Layer Deposition of MnOx,” ACS Appl. Energy Mater., vol. 3, no. 1, pp. 603–313, 2020.[6] M. P. Clark, T. Muneshwar, M. Xiong, K. Cadien, and D. G. Ivey, “Saturation Behavior of Atomic Layer Deposition MnOx from Bis(Ethylcyclopentadienyl) Manganese and Water: Saturation Effect on Coverage of Porous Oxygen Reduction Electrodes for Metal-Air Batteries,” ACS Appl. Nano Mater., vol. 2, no. 1, pp. 267–277, 2019.[7] M. Labbe, M. P. Clark, Z. Abedi, A. He, K. Cadien, and D. G. Ivey, “Atomic layer deposition of iron oxide on a porous carbon substrate via ethylferrocene and an oxygen plasma,” Surf. Coatings Technol., vol. 421, p. 127390, 2021.

Progress in the development of efficient electrocatalysts for oxygen reduction reactions is imperative for various energy systems such as metal-air batteries and fuel cells. In this paper, an innovative porous two-dimensional (2D) poly-iron-phthalocyanine (PFe-Pc) based oxygen reduction electrocatalyst created with a simple solid-state chemical reaction without pyrolysis is reported. In this strategy, silicon dioxide nanoparticles play a pivotal role in preserving the Fe-N4 structure during the polymerization process and thereby assist in the development of a porous structure. The new polymerized phthalocyanine electrocatalyst with tuned porous structure, improved specific surface area and more exposed catalytic active sites via the 2D structure shows an excellent performance towards an oxygen reduction reaction in alkaline media. The onset potential (E = 1.033 V) and limiting current density (I = 5.58 mA cm-2) are much better than those obtained with the commercial 20% platinum/carbon electrocatalyst (1.046 V and 4.89 mA cm-2) and also show better stability and tolerance to methanol crossover. For practical applications, a zinc-air (Zn-air) battery and methanol fuel cell equipped with the PFe-Pc electrocatalyst as an air cathode reveal a high open circuit voltage and maximum power output (1.0 V and 23.6 mW cm-2 for a methanol fuel cell, and 1.6 V and 192 mW cm-2 for the liquid Zn-air battery). In addition, using the PFe-Pc electrocatalyst as an air cathode in a flexible cable-type Zn-air battery exhibits excellent performance with an open-circuit voltage of 1.409 V. This novel porous 2D PFe-Pc has been designed logically using a new, simple strategy with ultrahigh electrochemical performances in Zn-air batteries and methanol fuel cell applications.

Self-powered electrochemical sensing platform based on zinc-air battery via synergy of the light filtering effect and photoassisted oxygen reduction reaction

High-performance rechargeable zinc-air batteries enabled by cobalt iron anchored on nitrogen-doped carbon matrix as bifunctional electrocatalyst

As one of the proposed post lithium-ion technologies, zinc-air batteries have received revived interest in the recent years, which is driven by the increased demand of high-performance, efficient, safe and environmentally friendly energy storage solutions. These energy storage systems need to address variable power, capacity and profitability requests. Zinc-air batteries with specific energy density higher than lithium-ion and low-cost, highly available, eco-friendly active materials are suitable to fulfill these requirements. The use of a flow battery type with zinc-particles suspended in alkaline solution (zinc-slurry) in addition with high performance oxygen-reduction electrodes enables the development of high-power zinc-air batteries. This setup also enables the independent scaling of capacity and power. The cooperative project, ZnMobil, founded by the Federal Ministry of Economic Affairs and Energy in Germany combines the experience of industrial and academic partners (Covestro Deutschland AG; Grillo-Werke AG; VARTA Microbattery GmbH; Accurec Recycling GmbH; Technical University Freiberg, Gottfried Wilhelm Leibniz University Hannover; University of Duisburg-Essen; the fuel cell research center ZBT GmbH) to develop a high-performance and low-cost zinc-air flow battery. Here we present strategies to improve the depth-of-discharge of zinc-air flow batteries. The battery system consists of a 100 cm² copper plate as current collector for the zinc-suspension electrode and an oxygen reduction electrode with gas-diffusion layer (supplied by Covestro). The zinc-slurry contains zinc particles (supplied by Grillo) suspended in alkaline solution (30 wt-% KOH) and stabilized with polyacrylic acid. The battery performance and depth-of-discharge were measured for several additives added to the zinc-slurry. Furthermore, the influence of the discharge current density on the depth-of-discharge was evaluated for these setups. Depending on the current density and additive selection, it is possible to achieve depth-of-discharge up to 90 %.

Highly efficient nitrogen-doped three-dimensional interconnected porous carbon supported heterogeneous Co/MnO nanoparticles oxygen electrocatalysts for rechargeable zinc air batteries

Developing efficient bifunctional catalysts for nonprecious metal-based oxygen reduction (ORR) and oxygen evolution (OER) is crucial to enhance the practical application of zinc-air batteries. The study harnessed electrostatic forces to anchor the nanoflower-like NiCo2O4 onto graphene oxide, mitigating the poor inherent conductivity in NiCo2O4 as a transition metal oxide and preventing excessive agglomeration of the nanoflower-like structures during catalysis. Consequently, the resulting composite, NiCo2O4-GO/C, exhibited notably superior ORR and OER catalytic performance compared to pure nanoflower-like NiCo2O4. Notably, it excelled in OER catalytic activity of the OER relative to the precious metal RuO2. As a bifunctional catalyst for ORR and OER, NiCo2O4-GO/C displayed a potential difference of 0.88 V between the ORR half-wave potential and the OER potential at 10 mA·cm-2, significantly lower than the 1.08 V observed for pure flower-like NiCo2O4 and comparable to the 0.88 V exhibited by precious metal catalysts Pt/C + RuO2. The NiCo2O4-GO/C-based zinc-air battery demonstrated a discharge capacity of 817.3 mA h·g-1, surpassing that of precious metal-based zinc-air batteries. Moreover, charge-discharge cycling tests indicated the superior stability of the NiCo2O4-GO/C-based zinc-air battery compared to its precious metal-based counterparts.

We report a hybrid battery that integrates a Zn-Ag battery and a Zn-air battery to utilize the unique advantages of both battery systems. In the positive electrode, Ag nanoparticles couple the discharge behaviors through the two distinct electrochemical systems by working as the active reactant and the effective catalyst in the Zn-Ag and Zn-air reactions, respectively. In the negative electrode, in situ grown Zn particles provide large surface areas and suppress the dendrite, enabling the long-term operating safety. The battery first exhibits two-step voltage plateaus of 1.85 and 1.53 V in the Zn-Ag reaction, after which a voltage plateau of 1.25 V is delivered in the Zn-air reaction, and the specific capacity reaches 800 mAh gZn-1. In addition, excellent reversibility and stability with maintaining high energy efficiency of 68% and a capacity retention of nearly 100% at 10 mA cm-2 are demonstrated through 100 cycles, outperforming both conventional Zn-air and Zn-Ag batteries. This work brings forth a conceptually novel high-performance battery, and more generally opens up new vistas for developing hybrid electrochemical systems by integrating the advantages from two distinct ones.

A Fe-Ni-Zn triple single-atom catalyst for efficient oxygen reduction and oxygen evolution reaction in rechargeable Zn-air batteries

Renewable energy systems and designing economically viable electrochemical energy storage systems is essential to decrease environmental pollution concerns while meeting the growing energy demand. Among the various energy storage devices, rechargeable zinc-air batteries (RZAB) have attracted great attention due to their relatively high specific energy (1218 W.h/kg), and volumetric energy density (6136 W.h/L) cost-effectiveness, and environmental friendliness, comparable to that of lithium–air batteries [1]. However, the sluggish kinetics of the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) during the discharge and recharge process of the air cathode on RZAB prevents large-scale application. So far noble metals (Pt, Ru, Ir) and their alloys (Pt-Ru/C) are used as bifuctional oxygen electrocatalysts in commercial rechargeable RZAB, yet they are too expensive to be viable for large-scale commercial applications. Therefore, designing robust and cost-effective bifunctional oxygen electrocatalysts is prime of importance for RZAB to be commercialized [2]. One of the most promising oxygen bifunctional catalyst are perovskite oxides due to their structural and compositional flexibility [3]. Moreover, the electronic structure of perovskite oxides can be tuned by varying the transition metals at the B site and thus their electrocatalytic performance [4-5].In this work, first we will demonstrate phase pure fabrication of double perovskite oxide series of NdBaCoXO5+δ (X= Fe, Ni, Mn). Second, OER and ORR performances of the series of NdBaCoXO5+δ (X= Fe, Ni, Mn) will be explained in relation with their electronic structure and work function. Here, we applied NdBaCoMnO6 on a home-made RZAB as air cathode, according to its bifunctional index. Therefore, we will finally present charge-discharge performance of RZAB with NdBaCoMnO6 as air cathode. J. Fu, Z. P. Cano, M.G. Park, A. Yu, M. Fowler, Z. Chen, Advanced Materials, 29, 1604685 (2016).Y. Tong, J. Wu, P. Chen, H. Liu, W. Chu, C. Wu, Y. Xie, Journal of the American Chemical Society, 140, 11165-11169 (2018).W. Yin, B. Weng, J. Ge, Q. Sun, Z. Li, Y. Yan, Energy & Environmental Science, 12, 442-462 (2019).J. Ahmed, N. Alhokbany, M. Ubaidullah, S. Mutehri, M. M. Khan, S. M. Alshehri, Ceramics International, 46, 20038-20044 (2020).A. Mulder, N. Benedek, J. Rondinelli and C. Fennie, Advanced Functional Materials, n/a-n/a (2013).

Rechargeable zinc-air batteries (RZBs) demonstrate significant potential as next-generation batteries as they are non-flammable, resource-abundant, cost-efficient, feasible for ambient air operation, and have remarkable theoretical energy density (1086 Wh kg-1). However, the development of RZBs needs to address many challenges to speed up their commercialization. For example, low round-trip efficiency during cycling is caused by retarded reactivity of the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) at the air cathode. An air cathode with deficient electrocatalytic kinetics creates a large voltage gap, especially when the practical charge voltage is > 2.0 V, during the charging and discharging process. Moreover, the cycle life of the RZBs is limited owing to the structural degradation of air cathodes working under high charge voltage. Therefore, it is essential to improve both the round-trip efficiency and structural durability of air cathodes to ensure further development and commercialization of RZBs. For efficient energy generation and storage, photo-enhanced RZBs that combine photochemical and electrochemical energy conversion and storage with the help of solar energy, are a promising research focus. Photo-enhanced RZBs require a photoactive OER/ORR bifunctional cathode that is not merely an electrochemical catalyst but also a photo-active catalyst.In the present study, we developed a photoactive bifunctional air-electrocatalyst with a staggered p-n heterojunction band gap structure, comprising n-type g-C3N4 and p-type copper-doped ZIF-67 (CuZIF-67) composite, to accelerate sluggish OER/ORR processes via a durable structure and stable long-cycle-life performance for photo-enhanced RZBs. g-C3N4/CuZIF-67 has a suitable band gap, which ensures wide-range light absorption in the UV–Vis–NIR region, and stimulates more electrons to participate in ORR/OER electrocatalytic activity. Besides, it has a staggered bandgap structure and a BEF at the p-n junction of the catalyst, which improves electron–hole pairs separation efficiency, lowers overpotential, promotes ORR/OER electrocatalytic activity, and eventually enhances the efficiency of RZBs (the voltage gap was significantly decreased by 14% with simulated solar light irradiation). Moreover, a high concentration of pyrrolic-N groups in the cathode material, resulting in the excellent electrochemical durability of RZBs during charge/discharge cycles. The photo-enhanced RZB based on the g-C3N4/CuZIF-67 bifunctional catalyst exhibits good round-trip efficiency of 60% (2 mA cm-2) with a significantly decreased voltage gap (from 0.92 to 0.81 V) after 1000 cycles, under simulated solar light irradiation. It can be concluded that staggered p-n heterojunction and pyrrolic nitrogen-rich groups play an important role in efficient and durable photo-enhanced Zn-air batteries.

As one of the most promising power sources in converting and storing chemical energy, aqueous zinc-air batteries (ZABs) stand out because of their high theoretical energy density, low cost, high safety of aqueous electrolyte, and environmental friendliness. Three main types of ZABs including primary ZABs, mechanically rechargeable ZABs, and electrically rechargeable ZABs have been developed up to now.[1] Primary ZABs for single use are usually discarded after the Zn anode is consumed or passivated although other parts of battery remain intact, leading to enormous waste. To address it, the depleted anode and failure electrolyte can be physically replaced to recover the capacity in mechanically rechargeable ZABs. But the cumbersome disassembly/reassembly process and the performance deterioration after every recharge process limit its practical application. In addition, it is not feasible to replace zinc in some integrated systems, such as the large-scale ZAB stack. Electrically rechargeable ZABs with bifunctional oxygen reduction reaction (ORR)/oxygen evolution reaction (OER) catalysts could be returned to the original state by electrochemical charging process, but also face some formidable challenges, such as dendritic zinc deposition, electrode deformation, and hydrogen evolution, limiting the long-term cycling performance. Besides, sluggish kinetics of ORR/OER and Zn passivation result in low energy efficiency, limited depth of discharge and power density. Especially in the resource-constrained and off-grid region, there isn’t external electricity source to charge the electrically rechargeable ZABs which limits their applications. Moreover, the reactions inherently take place on the surface of Zn anode and air cathode, in which the storage and conversion capability of the cell would be essentially constrained by the surface area of electrode and the volume of electrode compartment.The concept of redox targeting (RT) of battery materials offers a feasible solution to address these issues by employing redox mediators (RMs). To tackle the above challenges, here we demonstrate a redox-mediated Zn-air fuel cell (RM-ZAFC) based on the RT reactions of cobalt triisopropanolamine complex (CoTiPA) with O2 and 7,8-dihydroxy-2-phenazinesulfonic acid (DHPS) with Zn metal in the catholyte and anolyte, respectively. Both the 4-electron (4 e-) ORR and Zn oxidation reactions are liberated from the electrode surface and occur inside separate reactor tanks resorting to the RT processes. Upon operation, Co(III)TiPA in the catholyte is electrochemically reduced to Co(II)TiPA on the cathode and chemically oxidized back through ORR in the gas diffusion tank (GDT) into which O2 is fed. In conventional ZABs, ORR takes place on the triple-phase reaction interface of the heterogeneous electrocatalyst, and the catalytic performance is closely related to the density of exposed active site, electrical conductivity and reaction energy barrier. As compared, the redox-mediated ORR in GDT occurs homogeneously in the catholyte in which the dissolved RM could provide a large quantity of rection sites with tunable reaction energy barrier. For the negative side, DHPS-2H is firstly oxidized to DHPS on the anode and circulated into anodic tank, where it is regenerated by oxidizing Zn to ZnO. The discharge product ZnO is formed and deposited on the Zn granules loaded in the tank. After fully discharged, the cell can be feasibly refueled by replacing the Zn granules in the tank instead of disassembling and reassembling the whole cell. In this RM-ZAFC, the energy storage unit is decoupled from the power generation unit, thus offering greater operation flexibility and system scalability with modular design than the conventional ZABs. Compared with the commercial hydrogen tank used in hydrogen fuel cells, Zn granules loaded in the anodic tank present much higher volumetric capacity, greater safety and ease for storage and transportation. Therefore, as an energy conversion and storage device, RM-ZAFC would have great promise for automotive, backup, and stationary power applications.[2] In addition, we also propose an efficient and zinc regeneration method by RT reaction between RM and the product ZnO in RM-ZAFC to avoid the waste of ZnO and reduce the cost.

Implementation of renewable energy into the power grid is a necessary step for a more sustainable future. However, this process is strongly dependent on the capacity of practical energy storage technologies available. Zinc-air batteries show great promise for energy storage, boasting high theoretical energy density, inexpensive electrode materials, and excellent safety. Current development of zinc-air batteries is, however, stifled by the sluggish oxygen kinetics occurring both during discharge and charge. While precious metals such as platinum and ruthenium are considered to be good catalysts, more abundant, inexpensive transition metal catalysts have been found to perform just as well and with better cycling stability [1], [2].This work focuses on the development of transition metal oxide catalysts using atomic layer deposition (ALD). ALD is a gas phase deposition technique that generates conformal thin films through the use of self-terminating surface reactions. In particular, iron oxide catalysts, which promote the oxygen evolution reaction, are synthesized via ALD using an ethylferrocene precursor. Iron oxide growth from this precursor is enabled by an oxygen plasma reactant. Recipe development is showcased, demonstrating saturating behaviour for the growth of iron oxide films.The synthesized catalytic films are deposited directly onto a porous carbon substrate (gas diffusion layer or GDL), which is used as the air electrode in metal-air batteries. The high surface area GDL takes full advantage of ALD’s conformal nature to maximize the surface area of the deposited catalytic film, optimizing catalytic performance. As well, compared with other deposition techniques, ALD increases the depth of catalytic loading into the pores of the electrode. This increases the three-phase boundary volume consisting of gaseous oxygen, aqueous hydroxide ions, and solid catalytic active sites, thereby improving battery performance [3]. Deposited iron oxide films are tested through various electrochemical techniques to quantify catalytic activity. Iron oxide is combined with other transition metal oxides with the goal of creating a bifunctional catalyst, which is active for both the charge and discharge reactions in a zinc-air battery.[1] M. Xiong, M. P. Clark, M. Labbe, and D. G. Ivey, “A horizontal zinc-air battery with physically decoupled oxygen evolution/reduction reaction electrodes,” J. Power Sources, vol. 393, pp. 108–118, 2018.[2] D. Aasen, M. Clark, and D. G. Ivey, “A Gas Diffusion Layer Impregnated with Mn3O4 -Decorated N-Doped Carbon Nanotubes for the Oxygen Reduction Reaction in Zinc-Air Batteries,” Batter. Supercaps, vol. 2, pp. 1–13, 2019.[3] Y. Li and H. Dai, “Recent advances in Zinc-air batteries,” Chem. Soc. Rev., vol. 43, no. 15, pp. 5257–5275, 2014.

Technologies for extending zinc–air battery’s cyclelife: A review

In recent years, the rapid growth of portable electronic devices requires the high-energy density characteristics of batteries. Zinc air batteries have specific capacity as high as 820mAh/g. However, Zinc air batteries used for hearing aid applications only so far, because the atmosphere could affect it, and it has weakness in the rate capability. However, recent developments of electrode manufacturing technologies made us to overcome that weakness. And the efforts of applying zinc air batteries to portable electronic devices, especially in cellular phone application have been increased. In this paper, the effects of conducting material and polymer binder in cathode on the electrochemical characteristics were investigated. Our research team succeeded in producing 2.4Ah class zinc air battery for cellular phone application. Its volumetric energy density was 920 wh/l, and gravimetric energy density was 308 wh/kg. The volumetric energy density of our zinc air battery is two times higher than one of lithium secondary battery, and three times higher than that of alkaline manganese battery.