CHEMICAL SCIENCE

Interface science helps proton ceramic membrane fuel cells to make new breakthroughs


The Ding Dong team at Idaho National Laboratory/ The MIT Li Ju team achieved the intrinsic electrochemical properties of the perovskite proton conductor electrolyte in a full battery for the first time through interface engineering. At 23:00 on April 20, 2022, the study was published in the journal Nature under the title “Revitalizing interface in protonic ceramic cells by acid etch”.

The corresponding authors of the article are Wu Wei, Dong Yanhao, Li Ju and Ding Dong; the first authors are Bian Wenjuan and Wu Wei.

In the profound transformation of global energy, hydrogen energy is not only the preferred energy carrier for efficient decarbonization of electricity, but also as a medium for energy interconnection such as electricity, heat and gas to achieve collaborative optimization of cross-energy networks. As an important part of the energy transition, clean energy electrolyzed water can be used to produce hydrogen, and hydrogen can be used as a clean energy source to provide electricity to overcome the intermittent and unstable nature of sustainable energy sources such as solar and wind energy. Solid-state fuels/electrolytic batteries (PCFC/PCEC) with proton-conducted oxides as the electrolyte can efficiently generate electricity with zero emissions in a reversible reaction mode of hydrogen production. In PCFC/PCEC, the oxide electrolyte with the perovskite structure is the core component of proton conduction. However, due to the difficult sintering characteristics of such electrolyte materials, the preparation process of solid-state batteries is often accompanied by a high-temperature sintering process. This process often results in a large battery ohm resistance, affecting the interface of the electrolyte and oxygen electrodes, which in turn reduces battery performance and even seriously affects its service life.

Recently, the Ding Dong team of Idaho National Laboratory/ MIT Li Ju team designed and realized the reactivation of the electrolyte surface after high temperature sintering by acid treatment, so that its bulk phase proton conductivity in the whole battery is close to the theoretical value of the block. Studies have shown that the combination of electrolyte-electrode interface and electrochemical-mechanical coupling are critical to the thermomechanical integrity, microstructural stability, electrochemical properties and the stability of the whole battery of ceramic electrochemical batteries. Compared to previous reports of researchers’ extensive optimization of electrode materials and structures, this work focuses on how to better integrate the electrodes with solid-state electrolytes to ensure that they perform their intrinsic performance in full-battery operation.

The corrosion of the surface of the electrolyte by concentrated nitric acid starts from the grain boundary and specific grains, and the roughness of the electrolyte surface increases from 0.28 μm to 0.77 μm after treatment, and the mechanical strength of the interface contact between the electrolyte-oxygen electrode is also greatly enhanced. In the preparation and integration of the electrolyte of the yttrium(Y)-doped impurity conductor, the precipitation of the Y element leads to the formation of an insulating phase (such as Y2O3). Acid corrosion can effectively remove the insulating phase that accumulates on the surface of the electrolyte and thus help achieve its intrinsic conductivity characteristics.

Figure 1: Surface acid treatment significantly improves the surface roughness of the electrolyte and the interfacial bonding strength of the electrolyte and oxygen electrodes after sintering.

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Figure 2: High-quality bonding of the acid-treated electrolyte and oxygen electrode interfaces after sintering.

The method of this acid treatment does not change the mechanism of electrode reaction and electrolyte proton conduction, but reduces the impedance by reducing the preinhet coefficient of the ohmic resistance and the interface polarization resistance. This shows that acid treatment can not only reactivate the intrinsic conductivity of the electrolyte, but also help to greatly improve the density and activity of the electrolyte-oxygen electrode-oxygen three-phase interface. In untreated control batteries, the electrolyte-oxygen electrode interface is weakly bonded and the contact area is low, making the three-phase interface unable to provide sufficient electrochemical reactivity. The catalytic reaction on the oxygen electrode side is forced to occur on the surface of the oxygen electrode material farther away from the interface, and the proton conduction at this time greatly increases the ohmic resistance. The acid-treated oxygen electrode-electrolyte interface binding effect is enhanced, and the effective contact area is increased, providing enough reaction sites for electrochemical catalysis, and then the electrolyte re-exhibits eigen phase proton conduction in the whole battery. The acid-treated battery can operate at temperatures as low as 350 °C, which is of great significance for mitigating elemental diffusion between materials, reducing the cost of connector materials and matching temperature ranges for other chemical processes. In fuel cell mode, the maximum power density can reach 1.62 W cm-2 at 600 °C. In the hydrogen electrolysis mode of water production, the electrolytic current density at 1.4 V and 600 °C is as high as 3.9 A cm-2, which far exceeds the results reported in other literature. At the same time, the long-term stability of the acid-treated solid-state battery in fuel cell mode and electrolyzed water mode is greatly improved.

Figure 3: The ohmic resistance and the interfacial polarization resistance decrease simultaneously after acid treatment.

Figure 4: Acid treatment significantly enhances the electrochemical properties of PCFC/PCEC.

Due to the simple operation, low cost and short experimental cycle, the acid treatment method can be directly applied to the preparation and mass production of large batteries (5×5 cm2, 10 × 10 cm2). At present, Idaho National Laboratory is already promoting related work. In addition to the application in ceramic fuel cells, this work provides a good reference for the optimization of electrochemical interfaces in devices such as lithium-ion batteries and all-solid-state batteries. (Source: Science Network)

Related paper information:https://doi.org/10.1038/s41586-022-04457-y



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