In this study, operando X-ray absorption spectroscopy (XAS) measurements were carried out on a newly developed O2 bi-functional gas diffusion electrode (GDE) for rechargeable Zn-air batteries, consisting of a mixture of α-MnO2 and carbon black. The architecture and composition of the GDE, as well as the electrochemical cell, were designed to achieve optimum edge-jumps and signal-to-noise ratio in the absorption spectra for the Mn K-edge at current densities that are relevant for practical conditions. Herein, we reported the chemical changes that occur on the MnO2 component when the GDE is tested under normal operating conditions, during both battery discharge (ORR) and charge (OER), on the background of more critical conditions that simulate oxygen starvation in a flooded electrode.
An efficient conversion of electrical energy into hydrogen could be one of the most important key issues for future green energy supply. In case of electrolyzer cells, this can be achieved by increasing the active surface of Ni-based electrodes. This is a crucial topic for the research of alkaline electrolyzer cells in terms of improving the cell performance. Typical coating processes are scalable and effective techniques that are well suited for this purpose. Variations of sintering process parameters (i.e. duration or temperature ramps) have a distinct impact on the homogeneity of the coating layer and its thickness as well as on possible media transport paths during cell operation. In this study, we analyzed the impact of the coating layers on the structure and morphology of the electrodes using laboratory X-ray computer tomography. We introduce a workflow that is based on machine learning algorithms which enable to distinguish between substrate and coating layers. More detailed information was obtained using FIB/SEM (focused ion beam/scanning electron microscopy). This multi-scale approach enhances the understanding of the sintering processes and serve as a basis for CFD simulations.
Electrolyzer cells are a way of converting and storing excess energy and releasing it again if needed. Beside Li-ion-based batteries, this technique would enable to overcome the intermittent day-dependent availability of electricity (like solar or wind power). The power density and the amount of raw materials needed for the assembly of such cells can be improved through optimized manufacturing processes, especially the sintering process of the electrodes. The sintering process is crucial for the overall performance of an electrolyzer cell. The electrical conductivity as well as the media distribution inside the pores during cell operation needs to be tuned. Hereby, nickel particles are sintered on a nickel substrate. Different substances such as binder and surfactant, are added to the Ni(OH)2 before the sintering process is started. Ni(OH)2 will be reduced to Ni, resulting in an additional Ni coating on the Ni substrate. Material densification, decrease of the porosity and active surface are the most relevant factors during this process. To meet all the requirements a well-balanced sintering process in mandatory. A sufficient electrical conductivity requires well detached particles, while an optimal media transport requires more and large pores. Both can be met by using nickel particles with a defined size distribution of the particle diameters, and a balanced sintering process which significantly affects the conductivity and pores sizes. Moreover, remaining oxidized Ni, which is not an electrochemically active material, decreases the active surface of the sintered material.
This study focuses on the two-phase flow system through newly developed porous nickel materials. Therefore, imaging techniques are combined with electronic measurements and simulations. To characterize these materials results were taken from focused Ion beam (FIB), synchrotron tomography and neutron radiography. Typical structures are coated meshes, foams or expanded metals. The structure of nickel particles was analyzed in 3D using machine learning algorithms for image segmentation. In-operando measurements were performed at the neutron source BER II at Helmholtz-Zentrum Berlin, Germany. Different electric loads and materials were tested in order to obtain additional information to the electronical measurements in terms of media distributions, see figure 1.
The authors gratefully thank the German Federal Ministry for Economic Affairs and Energy (BMWi, Project AEL3D, grant number 03ET6063B) for financial support.
Figure 1
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