The normalized LSV curve of the YRO during ORR based on the actual surface. The battery cycle curves of the rechargeable Zn-air batteries using the YRO and the mixture of Pt/C and IrO2 during charging and discharging processes at a current density of 10 mA cm–.
Introduction of electrocatalysts for Zn–air batteries
- Introduction
- Principle of Zn–air batteries
- Materials and chemistry for electrocatalysts
- Pyrochlore oxides as bi-functional electrocatalysts
- Scope and organization of this dissertation
However, a high surface area of the electrode can increase the corrosion rate of zinc metal. To date, Pt has been reported as the most excellent electrocatalyst for ORR due to the high catalytic activity.
All-solid-state cable-type flexible Zn–air batteries
Introduction
As for the conventional ZAB system, an aqueous 6 M KOH solution is widely used as an optimized electrolyte due to its high ionic conductivity and low viscosity.98 To obtain the solid electrolyte, the KOH-based gel polymer electrolyte (GPE) developed. reported using various polymers, such as poly(vinyl alcohol) (PVA), poly(ethylene glycol) (PEO), poly(vinylpyrrolidone) (PVP) and as gelling agents, which have ionic conductivities of ca. In addition, an NPMC based on silk fibroin for metal/nitrogen/carbon (M/N/C) catalysts with high catalytic activity for the ORR was synthesized to improve the ORR in the flexible cable-type ZAB.
Experimental detail
In our case, we used an as-received zinc plate with a width of 3 mm and a length of 10 cm, and the diameter and length of the cable-type flexible Zn-air battery were 8 mm and 7 cm, respectively. For this study, we used a cellophane template with a diameter of 8 mm and a length of 7 cm.
Results and discussion
Accordingly, the air electrode containing the Fe/N/C-900 is used for cable-type flexible ZAB. a) Current-voltage of stack-type Zn-air batteries with Fe/N/C-900 (with zinc granulate) and (b) discharge curve for discharge current density at 100 mA cm−2. On the other hand, the OCV of a cable-type Zn-air battery with Fe/N/C-900 electrocatalyst was 1.14 V.
Summary
Single crystalline pyrochlore nanoparticles with metallic conduction as efficient bi-
Introduction
Among various energy conversion and storage technologies, metal–air batteries with high power and energy density are promising candidates for the operation of portable devices and electric vehicles,1, 117 especially Zn–air batteries due to their long lifetime, low cost, and abundant zinc Zn deposition. -air batteries have a higher specific energy density (approx. 1084 Wh kg–. However, current electrocatalysts other than metal oxide-based materials have shown poor bifunctional electrocatalytic activity for both ORR and OER in rechargeable Zn-air batteries. Furthermore, pyrochlore has been oxides (A2B2O7–x) studied as possible electrocatalyst candidates for ORR and/or OER among metal oxide-based materials.
Therefore, high phase purity is required to investigate the intrinsic catalytic activities of pyrochlore oxides. In addition, the highly efficient Pb2Ru2O6.5 metal nanoparticles exhibit remarkable ORR and OER activities in half- and full-cells for primary and rechargeable Zn-air batteries.
Experimental detail
Primary Zn-air batteries test: For primary Zn-air batteries test based on pyrochlore oxides, 0.75 g zinc granules are used as an anode and 200 μL 6 M KOH was used as an electrolyte. The assembled primary Zn-air batteries were tested at a discharge current density of 20 mA cm-2. Testing of rechargeable Zn-air batteries: For testing primary Zn-air batteries based on pyrochlore oxides, 0.5 g zinc plate is used as anode and 2 mL 6 M KOH with 0.2 M ZnO as electrolyte.
The method of preparing the air electrode with catalysts is the same as for primary Zn-air batteries, except for the nickel mesh. The assembled rechargeable Zn-air batteries were tested at discharge/charge current densities of 10 mA cm–2.
Results and discussion
Electrocatalytic activities of pyrochlore oxide catalysts and reported metal oxide-based electrocatalysts for ORR in 0.1 M KOH saturated with O2. Electrocatalytic activities of pyrochlore oxide catalysts and reported metal oxide-based electrocatalysts for OER in 0.1 M KOH saturated with O2. In order to evaluate the activities of the pyrochlore catalysts, we performed tests of primary and rechargeable Zn-air batteries.
The discharge polarization curves of the pyrochlore and Pt/C catalysts were obtained by increasing the current density to 300 mA cm-2 (Figure 34a). For practical application, a current density of 20 mA cm–2 was chosen as the discharge rate of primary Zn–air batteries containing pyrochlore and Pt/C catalysts (Figure 34c).
Summary
Unveiling the catalytic origin of nanocrystalline yttrium ruthenate pyrochlore as a
Introduction
In terms of the catalytic activity and structural stability, metal oxides have been considered the most promising candidates, showing comparable electrochemical performances to the advanced Pt/C and IrO2 catalysts for ORR and OER, respectively.120 , 128 . 156 For example, Pb2 exhibited [Ru2–xPbx4+]O6.5, Pb2[Ir2−xPbx]O7−y and Bi2[Ru2–xBix]O7–y significantly improved electrochemical performance due to the high charge transfer through the oxygen vacancies.80, 138 It is reasonable to expect that a higher concentration of oxygen defects could improve the ORR and OER activities.73 However, the use of A-site cations in previous examples was still limited to divalent lead or trivalent bismuthions, thus resulting in a poor understanding of the pyrochlore structure .140, 142 For broad applications, the new approach should be explored with other A-site cations to identify the catalytic origin of the pyrochlore structure. Consequently, trivalent yttrium ions can be considered as A-site cations of the pyrochlore oxide due to the corresponding ionic radius with divalent lead or trivalent bismuth ions.157 Based on the Mott-Hubbard mechanism, the electrical behavior of the pyrochlore oxide is determined by the Ru-O-Ru bond angle, which corresponds to the size of A-site cations.158, 159 In this regard, the development of yttrium ruthenate (Y2[Ru2–xYx]O7–y) as a new electrocatalyst is necessary for a comprehensive understanding of pyrochlore structure.
Regarding the charge transfer of electrocatalysts during cycling, it is expected that it can be accompanied by redox reactions of pyrochlore oxides. Recently, in situ X-ray absorption spectroscopy (XAS) has been suggested to investigate the electron configurations and local geometrical structures of electrocatalysts in real time. 151, 160 The reported in situ XAS can be classified into two types based on in process measurements; that is, temperature-controlled synthesis or electrochemical analysis.
Experimental detail
The collection efficiency (N) was determined under Ar atmosphere using 10 mM K 3 [Fe(CN) 6 ], which is about 0.41. Primary Zn-air batteries test: For primary Zn-air batteries test based on YRO, 0.75 g zinc granules are used as an anode and 200 μL 6 M KOH was used as an electrolyte. The air electrode, which is a cathode, was made of uniformly loaded gas diffusion layer (GDL) (the catalyst ink formulation: 16 mg of catalyst, 4 mg of ketene black, 200 μL of 5 wt% of the Nafion solution, and 800 μL of ethanol on nickel mesh.
This prepared GDL was used as a reference for comparison to confirm the improved performance of the catalyst-based air electrode in the polarization curves of Zn-air batteries. Zn–air rechargeable battery tests: For YRO-based Zn–air rechargeable battery tests, 0.5 g of zinc plate is used as anode and 2 mL of 6 M KOH with 0.2 M ZnO as electrolyte.
Results and discussion
Moreover, the mass transfer-corrected Tafel plots indicated the kinetic reactions of the YRO and Pt/C for ORR (Figure 44). Moreover, the normalized LSV curve of the YRO was based on the actual surface area measured for practical catalytic activity (Figure 46). Furthermore, we performed the charge and discharge cycle tests of Zn–air batteries to investigate the structural stability of the YRO.
Normalized LSV curve of YRO during OER based on real surface. Figure 53b,c shows the oxidation state–scan number curves for the A and B site cations of YRO.
![Figure 37. Preparation, morphology and structural characterization of nanocrystalline pyrochlore oxides (A 2 [B 2–x A x ]O 7–y )](https://thumb-ap.123doks.com/thumbv2/123dokinfo/10497058.0/114.892.114.784.136.821/figure-preparation-morphology-structural-characterization-nanocrystalline-pyrochlore-oxides.webp)
Summary
Polyhedral bismuth ruthenate pyrochlore as a bi-functional oxygen electrocatalyst
Introduction
Among them, Zn-air batteries are the most promising candidate for practical application due to the high energy density, high safety and low cost of zinc metal. However, stack-type Zn-air batteries are limited in demonstrating very stable potential retention, due to the saturation of zincate ion (Zn(OH)42–) upon discharge. To increase zinc utilization, flow-type Zn-air batteries should emerge as promising candidates. In this regard, Zn airflow batteries are limited from the slow kinetics of oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), as well as those of stacking type12, 42.
In particular, we first observed the facet evolution of the polyhedrally shaped pyrochlore oxides in real time by in situ environmental transmission electron microscopy (TEM) spontaneously with heat treatment. Furthermore, the prepared pyrochlore oxide exhibits low overpotentials for ORR and OER, resulting in the significantly improved electrochemical performances of primary and rechargeable Zn air flow batteries.
Experimental detail
The capacitively corrected ORR and OER currents were ohmically corrected with the measured ionic resistance (≈45 Ω). Additionally, a ring potential of 0.4 V (vs. Hg/HgO) was applied to oxidize peroxide during ORR. Primary tests with Zn-air batteries: For tests with primary Zn-air batteries based on the polyhedral bismuthruthenate pyrochlore oxide, 0.75 g zinc granulate is used as anode and 200 μl 6 M KOH as electrolyte.
GDL was prepared from a mixture of activated carbon (Darco G-60A, Sigma-Aldrich) and PTFE binder (60 wt% PTFE emulsion in water, Sigma-Aldrich) in a weight ratio of 7:3 with a thickness of approx. . 450 μm to ensure correct gas distribution and sufficient current collection. Rechargeable Zn-air flow batteries test: For primary Zn-air batteries test based on polyhedral bismuth ruthenate pyrochloroxide, 0.5 g zinc plate is used as anode and 2 ml 6 M KOH with 0.2 M ZnO as electrolyte.
Results and discussion
These results can be attributed to significant enhancement of bifunctional catalytic activities of BRO. These results can be attributed to a greatly increased zinc utilization by the Zn air flow batteries. To demonstrate the practical applications of flow-type Zn-air batteries, the primary batteries containing BRO and Pt/C were subjected to the discharge tests at a current density of 25 mA cm-2 (Figure 56d).
Notably, the discharge capacity of BRO showed a significantly increased value comparable to that of Pt/C. Electrocatalytic activities of polyhedral BRO with pyrochlore structure. a) Linear scan voltammogram (LSV) curves of BRO and Pt/C during ORR.
Summary
Design principles for oxygen reduction activity on perovskite oxide catalysts for fuel cells and metal-air batteries. Ketjenblack metal-free, nitrogen-doped, gelatin-derived carbon sheets as catalysts for oxygen reduction. Highly efficient electrocatalyst for the oxygen reduction reaction: N-doped Ketjenblack embedded in Fe/Fe3C-functionalized melamine foam.
Spinel-type lithium cobalt oxide as a bifunctional electrocatalyst for oxygen evolution and oxygen reduction reactions. In situ X-ray absorption spectroscopy Investigation of a bifunctional manganese oxide catalyst with high activity for electrochemical water oxidation and oxygen reduction.
