Rechargeable Zn-air Batteries Research Articles

Tri-functional Ru-RuO2/Mn-MoO2 composite: A high efficient electrocatalyst for overall water splitting and rechargeable Zn–air batteries

Preparation of highly efficient multi-functional electrocatalyst is extremely useful for application but quite challengeable. Herein, a new tri-functional Ru-RuO2/Mn-doped MoO2 (RRMM) electrocatalyst was successfully prepared through a facile solid phase reaction strategy. RRMM catalyst exhibits the small overpotential of 15 and 260 mV for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) at a current density of 10 mA cm−2, respectively. A low cell voltage of 1.53 V is required to achieve a current density of 10 mA cm−2 for overall water splitting. Meanwhile, a half-wave potential of 0.83 V was needed for oxygen reduction reaction (ORR) and assembled Zn–air battery exhibits an excellent stability. Density functional theoretical calculations also revealed that Ru-RuO2 active units facilitated reaction kinetics of HER and OER, while the synergistic effect of Ru and Mn-doped MoO2 endowed RRMM catalyst with excellent ORR activity.

Bimetallic 3D hollow-nanoshell FeCo-oxynitride/N and S co-doped carbon nanotubes as a robust bifunctional oxygen electrocatalyst for rechargeable Zn-air batteries

Bimetallic 3D hollow-nanoshell FeCo-oxynitride/N and S co-doped carbon nanotubes as a robust bifunctional oxygen electrocatalyst for rechargeable Zn-air batteries

Surface reconstruction of SrCoO2.52 nanofibers as bifunctional oxygen electrocatalyst for rechargeable Zn-air batteries

Rechargeable metal-air battery is an emerging renewable energy technology with advantages of high efficiency, zero pollution and environmental friendliness. The development of efficient and cost-effective oxygen electrocatalyst plays a key role in tackling the performance restrain of air electrode for rechargeable metal-air batteries, especially for Zn-air batteries. Herein, we reported surface reconstruction on a complex metal oxide, SrCoO2.52 (SCO) utilizing selective ion corrosion to boost its activity for O2 electrocatalysis and Zn-air batteries. Based on the difference in bond strength between Sr–O and Co–O, a selective etching of Sr cation on the surface of SCO nanofibers has been realized using a gentle wet chemical method. The selective Sr etching altered both the crystal and electronic structure of the catalyst surface, reconstructing the surface to form a cobalt-rich layer over the SCO matrix. The obtained core-shell structure significantly enhanced the activity of the SCO catalyst for both the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR). The bifunctional SCO catalyst was applied as air electrode for rechargeable Zn-air batteries, delivering a power density of 191 mW cm-2 and a stability of 500 charging-discharging cycles outperforming that of the IrO2‖Pt/C composite (180 mW cm-2 and 100 cycles). The performance enhancement was proposed to be due to the surface reconstruction increasing the exposure and approachability of the active Co sites and improving the redox ability of the Co cations. This work not only presents an efficient method of reconstructing SCO with highly active surface for oxygen electrocatalysis and Zn-air batteries, but also may arouse interest to design advanced complex metal oxides with surface-regulating potential for various electrocatalytic applications.

Co single atoms building bifunctional catalysts for zinc-air batteries

High-efficiency bifunctional catalysts will improve the sluggish kinetics on the oxygen electrode for rechargeable Zn-air batteries (ZABs). This study designed hierarchical porous carbon to load Co single atoms (SAs) and highly graphitized carbon nanotubes to stabilize carbon substrate for enhancing the activity and stability of oxygen reduction reaction and oxygen evolution. As-prepared bifunctinal catalyst endowed with a smaller overall overpotential delivers superior efficiency in ZABs, outperforming the commercial Pt/C + RuO2, with a cycle life over 200 h. This work provides an efficient way to construct Co SAs bifunctional catalysts by introducing multi-dimensional carbon substrate.

Highly accessible atomically dispersed FeNx sites coupled with Fe3C@C core-shell nanoparticles boost the oxygen catalysis for ultra-stable rechargeable Zn-air batteries

It is significant but challenging to develop a cost-effective, high-efficiency, and stable bifunctional electrocatalyst of oxygen reduction and evolution reactions (ORR and OER) for rechargeable Zn-air batteries. Herein, we present a novel bifunctional catalyst constructed by highly accessible atomically dispersed MNx sites coupled with core-shell nanoparticles (M-Phen-800; M = Fe, Co, and Ni) from easily accessible M-Phenanthroline (M-Phen) complexes. Due to the synergistically induced symmetric charge distribution around FeNx sites by Fe3C@C core-shell nanoparticles, Fe-Phen-800 exhibits exceptional onset (Eonset = 0.994 V) and half-wave (E1/2 = 0.878 V) potentials for ORR and a very low overpotential of 285 mV @ 10 mA cm−2 (Ej=10) for OER, indicating excellent bifunctional activity (ΔE = Ej=10 - E1/2 = 0.637 V) over the state-of-the-art Pt/C-RuO2 (0.702 V) combination. Moreover, the Fe-Phen-800-based Zn-air battery demonstrates a remarkable energy density of 1022 Wh kg−1 and greater cycling stability (>800 cycles) than the commercial Pt/C-RuO2 battery.

Molybdenum-leaching induced rapid surface reconstruction of amorphous/crystalline heterostructured trimetal oxides pre-catalyst for efficient water splitting and Zn-air batteries

Crystalline and amorphous structure can entitle a catalyst with high stability and activity, respectively. Oxygen evolution reaction (OER) catalysts, which widely used in water electrolysis and rechargeable Zn-air batteries, often undergo a surface phase reconstruction process and generate amorphous active phases under applied anodic potential. Although widely known, few studies and strategies have been reported to rationally tune OER pre-catalysts for enhanced reaction kinetics. Herein, we report a trimetallic oxides (a/c-NiFeMoOx) OER per-catalyst with rationally tunable amorphous/crystalline heterostructure degrees by a precise-tuning component strategy. The best a/c-NiFeMoOx electrode exhibits an OER overpotential merely of 256 mV and a small cell-voltage of 1.52 V to reach 10 mA cm–2 for water electrolysis, respectively. It is find that Mo leaching with tailored amorphous/crystalline heterostructure via the rational tuned degree of amorphousness promotes a rapid surface reconstruction of the a/c-NiFeMoOx pre-catalyst to form (oxy)hydroxide active species, whilst operando Raman, ex-situ X-ray photoelectron spectroscopy and density functional theory (DFT) analysis show the ample oxygen vacancies generated by phase transition significantly accelerates the deprotonation of OH* and lower the O* ➝ OOH* free energy for a fast oxygen evolution kinetics. Additionally, the practical application of a/c-NiFeMoOx cathode in rechargeable Zn-air battery delivers a robust long-term cycling (over 840 cycles).

Novel design and synthesis of multi-anionic Co(OH)Se with ZIF-67 derived porous carbon matrix as a bifunctional electrocatalyst for rechargeable Zn-air batteries

Multi-anionic transition metal compounds with unique electron structures that are favorable for electron transfer are promising oxygen electrocatalysts. In this study, to synthesize a bifunctional oxygen electrocatalyst for Zn-air batteries (ZABs), unique structured composite of cobalt hydroxy selenide (Co(OH)Se) and nitrogen-doped carbon (C) was fabricated using a novel water vapor-assisted heat-treatment and an anion-exchange technique using a NaHSe solution. C@Co(OH)Se prepared under low-temperature and low-pressure condition successfully exhibited excellent electrocatalytic activities for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) via synergistic effects. Accordingly, C@Co(OH)Se-based ZAB displayed great cycle stability (discharge/charge potential gap of 1.01 V after 7,000 min cycling) and rate capability (1.25 V at 15 mA cm−2). By first demonstrating the potential use of multi-anionic Co(OH)Se as a bifunctional electrocatalyst for the ORR/OER and presenting a technique for complexing transition metal compounds and carbon matrices, our study expands the range of electrocatalyst design and synthesis.

Engineering bifunctional electrocatalysts for rechargeable Zn-Air battery by confining Co–Zn–Mn in flower-structured carbon

The performance of Zn-Air battery (ZAB) is often limited by sluggish kinetics of oxygen reduction reaction (ORR) and oxygen evolution reactions (OER). In this work, a flower-like porous carbon is designed for the synthesis of the Co/Zn/Mn@NC. Due to a highly porous structure and abundant active sites, the as-prepared Co/Zn/Mn@NC-800 shows a half-wave potential of 0.86 V for ORR, and an overpotential of 360 mV for OER at 10 mA/cm2, suggesting an excellent bifunctional catalytic activity. The ZAB with Co/Zn/Mn@NC-800 delivers a power density of 163 mW/cm2 and a specific capacity of 832 mA h/gZn, higher than that with Pt/C + RuO2 (147 mW/cm2 and 802 mA h/gZn). Moreover, the Co/Zn/Mn@NC-800-based ZAB has a superior long-term stability with a negligible decline of efficiency (0.3%) after 534 cycles (>150 h). These results suggest that the synthesized Co/Zn/Mn@NC catalyst has a great potential for the practical application in ZABs.

Highly accessible platinum with low-loading embedded in hierarchically porous carbon fiber for efficient oxygen reduction reaction

Improving the utilization efficiency of platinum (Pt) is required for realizing the efficient oxygen reduction reaction (ORR) in rechargeable Zn–air battery (ZAB). Herein, a carbon fiber decorated with coexistence of uniformly dispersed Pt nanoparticles and Pt-N-C moieties (Pt-HPCF) is synthesized and used as electrocatalyst for ORR. The elaborately structural design of Pt-HPCF catalyst on atomic/nanoscopic, mesoscopic and macroscopic level guarantees highly accessible activity sites, fast reactants transport, rapid electron transfer, and strong metal-support interaction. Benefited from the multi-level synergistic optimization, this unique Pt-HPCF electrocatalyst with ultralow Pt loading presents excellent ORR activity with a mass activity of 912.08 mA mg−1 at 0.85 V, which is 7.5 times that of the corresponding value for commercial Pt/C catalyst. Moreover, Pt-HPCF also exhibits high stability after accelerated degradation test. Furthermore, ZAB assembled with Pt-HPCF catalyst exhibits a high open circuit voltage (OCV) of 1.576 V, high capacity of 840 mAh g−1 at 5.0 mA cm−2, and a large peak power density of 163.38 mW cm–2. This work provides a feasible route for optimizing the Pt or other metal-based electrode in energy storage/conversion fields.

Synergetic Nanostructure Engineering and Electronic Modulation of a 3D Hollow Heterostructured NiCo2O4@NiFe-LDH Self-Supporting Electrode for Rechargeable Zn–Air Batteries

Developing electrocatalysts that integrate the merits of the hollow structure and heterojunction is an attractive but still challenging strategy for addressing the sluggish kinetics of oxygen evolution reaction (OER) in many renewable energy technologies. Herein, a 3D hierarchically flexible self-supporting electrode with a hollow heterostructure is intentionally constructed by assembling thin NiFe layered double hydroxide (LDH) nanosheets on the surface of metal-organic framework-derived hollow NiCo2O4 nanoflake arrays (NiCo2O4@NiFe-LDH) for rechargeable Zn-air batteries (ZABs). Theoretical calculations demonstrate that the interfacial electron transfer from NiFe-LDH to NiCo2O4 induces the electronic modulation, improves the conductivity, and lowers the reaction energy barriers during OER, ensuring high catalytic activity. Meanwhile, the 3D hierarchically hollow nanoarray architecture can afford plentiful catalytic active sites and short mass-/charge-transfer pathways. As a result, the obtained catalyst exhibits remarkable OER electrocatalytic performance, showing low overpotentials (only 231 mV at 10 mA cm-2, 300 mV at 50 mA cm-2) and robust stability. When assembling liquid and flexible solid-state ZABs with NiCo2O4@NiFe-LDH as the OER catalyst, the ZABs achieve excellent power density, high specific capacity, superior cycle durability, and good bending flexibility, exceeding the RuO2 + Pt/C benchmarks and other previously reported self-supporting catalysts. This work not only constructs an advanced hollow heterostructured catalyst for sustainable energy systems and wearable electronic devices but also provides insights into the role of interfacial electron modulation in catalytic performance enhancement.

Bamboo fiber–derived bifunctional electrocatalyst for rechargeable Zn-air batteries

Low-cost and high-performance bifunctional electrocatalysts for efficient oxygen reduction reaction (ORR)/oxygen evolution reaction (OER) are vital for the applications of rechargeable Zn-air batteries (ZABs). Herein, a porous carbon material is fabricated by traditional pulp and papermaking and carbonization process from bamboo. The resultant carbon paper catalyst possesses a high surface area, porous structure, and high content of nitrogen. Benefiting from these characteristics, this material exhibits remarkable ORR and OER catalytic performances. The aqueous rechargeable Zn-air batteries assembled with this catalyst exhibit a high power density of 279.5 mW cm−2. This work paves an encouraging way for the industrial production of cost-effective catalysts in a sustainable manner.

The influence of different air electrode structures to discharge characteristics in rechargeable Zn-air battery

The rechargeable metal-air battery technology is a well-interested smart method for eco-friendly and sustainable energy storage. Both of the two order of magnitude lower global market price per tonne of Zn compared to lithium and the multiple theoretical and practical specific energy density of rechargeable ZAB compared to the worldwide Li-ion designs contributes the developing continuously of rechargeable Zn-air battery. The air electrode as a cathode has a vital role in increasing the discharge-charge performance in ZABs, therefore different layers-order air electrodes were assembledwith the utilization of Ni-foam, graphite coating and carbon nanoparticles. The tri-layers cathode showed the highest voltage and performance values compared to the mono- (Ni-foam) and bi- (Ni-foam + graphite coating) layers architectures. The effect of electrolyte inorganic additives (e.g., 2 n/n% ZnCl2 and 0,05 wt% MnO2) was experienced especially at the no-load period.

CuO/Co3O4 heterostructures with carbon nanotubes composites as ORR/OER electrocatalysts for Zn-air batteries

Rechargeable Zn-air batteries (ZABs) constitute promising next-energy conversion and storage systems due to their low cost, intrinsic safety, and feasibility to fabricate high energy density and stable charge and discharge voltage. Nevertheless, the most significant challenge of rechargeable ZABs is relatively high over potential owing to the sluggish kinetics of oxygen reactions on the air cathode, requiring high-performance noble-metal-free bifunctional electrocatalysts with highly cost-effective. Herein, we developed a facile and scalable coprecipitation strategy to successfully prepare CuO/Co3O4@CNTs catalysts for bifunctional oxygen electrocatalysts. This unique strategy enables CuO/Co3O4 nanoparticles to be uniformly grown on CNTs and the simultaneous pyrolysis process results in the generation of ultrafine CuO/Co3O4 heterostructures. Contributed to an abundance of heterostructures, the oxygen vacancies and unsaturated chemical bonds in the interface were generated in CuO/Co3O4. Consequently, the CuO/Co3O4@CNTs delivered bifunctional activity of ΔE of 0.78 V and good stability that can maintain 1000 h charge and discharge cycles.

A high-voltage Zn-air battery based on an asymmetric electrolyte configuration

Rechargeable Zn-air batteries promise safe energy storage. However, they are limited by the redox potential of O2/O2- chemistry in an alkaline electrolyte, resulting in low operating voltages and therefore insufficient energy density to compete with lithium-ion batteries. The O2/O2- redox potential increases by 0.8 V in an acidic medium, hinting at a way to boost the voltage: an asymmetric electrolyte configuration decoupling acidic and alkaline electrolytes for the air cathode and zinc anode. Such configuration requires a thin and ionically conductive membrane to separate two mutually incompatible electrolytes. Here, we report a Zn ion-exchange membrane with high ionic conductivity of 1.1 mS cm-1, which prevents acid-base neutralization. The highly reversible O2/O2- reaction in the acid is made possible by compositing a cobalt-coordinated porphyrin-based polymeric framework with MXene as a bifunctional electrocatalyst. The asymmetric Zn-air battery operates at voltages up to 1.85 V and cycles for more than 200 h with a material-level energy density of 1350 Wh kg-1, projected to a high device-level energy density of 50 Wh kg-1 (coin cell diameter: 20 mm). The asymmetric configuration withstands pressure up to 4 MPa (∼1200 N), demonstrating excellent structural stability for production and practical applications.

NaCl sealing Strategy-Assisted synthesis CoO-Co heterojunctions as efficient oxygen electrocatalysts for Zn air batteries

Developing highly efficient, low-cost, and stable bifunctional oxygen electrocatalysts is essential for the wide popularization of rechargeable Zn-air batteries. Combining zero-dimensional metal nanoparticles with two-dimensional metal oxide nanosheets is an appealing strategy to balance performance and cost. However, the precise construction of these composites remains a great challenge, and their interaction mechanisms lack thorough study. Herein, a cobalt-oxide-based bifunctional oxygen electrocatalyst comprising a rich Co-CoO heterointerface (CoO/Co@NG) was synthesized via a NaCl sealing-assisted pyrolysis strategy. The NaCl crystals played the role of a closed nanoreactor, which facilitated the formation of a CoO-Co heterojunction. Experimental results and theoretical calculations confirmed that the ingeniously constructed heterojunction expedited the oxygen reduction reaction and oxygen evolution reaction kinetics, which is superior to Pt/C. When serving as the air electrode in an assembled liquid-state Zn-air battery, the battery shows high power density (215 mW cm−2), specific capacity (710 mAh gzn−1), and outstanding durability (720 h at 10 mA cm−2). This work provides an innovative avenue to design high-performance heterojunction electrocatalysts for perdurable Zn-air batteries.

Structure-performance relations for carbons in Zn-air battery cathodes with non-alkaline electrolytes

Rechargeable Zn-air batteries (RZABs) with non-alkaline electrolytes are a promising type of energy storage devices that potentially combine low cost, high energy density and safety. However, cathode materials for these devices remain poorly developed. We present a systematic study of how structure of carbons affects their performance as cathode scaffolds in non-alkaline RZABs. Ten commercially available types of carbon are characterized and tested in Zn-air battery cathodes with 1 M Zn(OAc)2 or ZnSO4 solutions in H2O as electrolytes. At a low current density (0.1 mA cm−2), there is a roughly linear dependence between the roundtrip energy efficiency and the logarithm of BET surface area, and this dependence is relevant across materials with different morphology and graphitization degree. Lower overpotentials at the initial cycles are observed for cathodes that are more hydrophilic. At higher currents (1 mA cm−2), morphology plays an important role for oxygen reduction kinetics, with nanosized carbons having a much better performance compared to microporous materials with micron-sized particles. Overall, the best performance in non-alkaline RZABs is achieved for nanosized carbons with high specific surface area (>450 m2g− 1). Our findings help to formulate structural and morphological guidelines for choosing or synthesizing an optimal carbon scaffold for RZABs.

Boosting Urea Electrooxidation Activity of Ni5P4 by Vanadium Doping for Urea-Assisted Renewable Energy Conversion Devices

The urea oxidation reaction (UOR), a competitive substitute for the oxygen evolution reaction (OER), holds superior potential to meet the upsurge of renewable energy conversion due to low theoretical potential while the sluggish UOR kinetics impede its practical application. In this report, for the first time, we demonstrate that the UOR activity of Ni5P4 is improved via V incorporation. The novel amorphous V-doped Ni5P4 (V10%-Ni5P4) microflower structure with optimized electronic structure was prepared by a solvothermal–phosphorization process. With V atoms involved, the V10%-Ni5P4 microflowers are assembled by much thinner, denser nanosheet units compared with the Ni5P4 counterpart, which endows it with more active sites, enhanced mass transfer, conductivity, and better wettability. The V10%-Ni5P4 microflowers exhibit outstanding UOR activity of 282 mA cm–2 at 1.6 V vs RHE with a low Tafel slope (36.1 mV dec–1). Furthermore, the urea-assisted electrolytic cell only needs 1.44 V to provide 50 mA cm–2 and the urea-assisted rechargeable Zn-Air battery (uZAB) is illustrated to have a higher open-circuit voltage of 1.43 V and possesses a lower potential gap than that Pt/Ir-based uZABs. This report sheds light on the role of vanadium in crystallization and structure optimization and lays the foundation for developing new UOR electrocatalysts.

Metal-mediated Schiff base polymer enables metal/nitrogen codoped carbon nanosheets as efficient bifunctional electrocatalyst for durable rechargeable Zn-air batteries

We report a simple yet robust route to bifunctional electrocatalysts comprising FeNi and Co4N hybrid nanoparticles co-embedded within N-doped carbon nanosheets (denoted FeNi/Co4N-NCS) for rechargeable Zn-air batteries (ZABs) with high power density and capacity as well as outstanding cycling stability, markedly outperforming the Pt/C&IrO2 electrocatalyst counterpart. The as-crafted FeNi/Co4N-NCS electrocatalysts display outstanding bifunctional oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) activity with a low overall oxygen electrode activity (ΔE = 0.664 V). Density functional theory (DFT) calculations reveal that the synergy of FeNi and Co4N reduces the rate-determining step (RDS) energy barrier, thereby greatly increasing electrocatalytic activity. The aqueous ZAB assembled with FeNi/Co4N-NCS delivers a high power density of 160 mW cm−2, large specific capacity of 812 mAh g−1Zn, and long cycling life of 1450 h at 5 mA cm−2. This study highlights an effective strategy to yield durable bifunctional electrocatalysts for metal-air batteries.

Electrocatalytic performance of Ni-promoted Co nanoclusters supported by N-doped carbon foams for rechargeable Zn-air batteries

Ni/Co diatomic clusters supported on nitrogen-doped carbon foams are prepared via molten salt method to improve the density of surface active sites of zinc-air battery catalysts and further explore metal-modified carbon-based catalysts. The influence of Co and Ni atoms on the carbon foam structure is investigated by X-ray diffraction and high-resolution electron microscopy, and the presence of metal atoms in N-doped carbon foams is confirmed by X-ray spectroscopy. The left shift of the diffraction peak of Co doped graphitic carbon indicates an increase in the interlayer spacing and a reduced graphitization degree, while the introducton of Ni atoms promotes graphitization. For Ni–Co/NFC-2, Ni inhibits the insertion of Co in carbon layer by increasing graphitization, thus exposing more Co-active substances on the surface, which is important for improving the catalytic process of ORR and OER. According to electrochemical tests, Ni–Co co-doped carbons exhibited superior bi-functional electrocatalytic performance with oxygen reduction reaction (ORR) Eonset = 0.97 V and a Tafel slope of 49.5 mV dec−1, accompanied by oxygen evolution reaction (OER) Ej = 10 mA cm−2 = 1.46 V. Zinc-air battery (ZAB) cell, utilizing the developed material as a catalyst, exhibited a high discharge power density of 138 mW cm−2 with stable performance for up to 200 h.

Atomically dispersed Fe-Ni dual sites in heteroatom doped carbon tyres for efficient oxygen electrocatalysis in rechargeable Zn-Air battery

The electronic and functional synergies between the twin metal centers make dual single-atom catalysts (DACs) attractive for oxygen electrocatalysis. The catalytic activities of DACs are largely decided by their surrounding micro-environment and supporting substrates. Modulating the micro-environment as well as engineering the efficient support is challenging tasks. Moreover, both are critical to optimizing the performance of DACs. Herein, a novel bio-cooperative strategy is developed to synthesize FeNi-DAC wherein Fe-Ni dual-atom sites are embedded in the N, P codoped tyre shaped carbon matrix. The configuration matching of Fe-Ni dual centers together with the local electronic engineering of N, P heteroatoms synergistically boost the catalytic activity on the oxygen reaction. Furthermore, the central-hollow highly-porous carbon matrix not only gives rise to a large amount of active sites, but also facilitates fast kinetics. Taking advantage of both the DAC and the substrate, the FeNi-NPC hollow tyre (HT) catalyst scores high in both oxygen reduction and evolution reactions, which exhibits the narrow potential difference and excellent durability. The aqueous Zn-air full battery (ZAB) integrating the FeNi-NPC HT air cathode has a high power density and a good stability over long-term cycling. Moreover, the flexible solid-state ZAB assembled with the polymer electrolyte obtains the high reliability over a wide range of temperatures or under diverse outside deformations. Therefore, this work offers a new green approach to prepare highly efficient DACs with built-in modulated micro-environment and tailor-made substrates. Moreover, it also paves a new way to develop highly-pliable power source for flexible electronics.