The two-fold diffusion process for proton uptake reaction in BCFZY e - /H + /O 2- triple conductor measured by electrica
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The two-fold diffusion process for proton uptake reaction in BCFZY e-/H+/O2- triple conductor measured by electrical conductivity relaxation Tao Hong 1 & Weihua Lu 1 & Keke Ren 1 & Tong Liu 2 Received: 28 July 2020 / Revised: 18 August 2020 / Accepted: 24 August 2020 # Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract For materials as BaCo0.4Fe0.4Zr0.1Y0.1O3-δ with three independent mobile charge carriers, hole, oxygen ion, and proton, a peculiar twofold diffusion and transition from hydration to hydrogenation in proton uptake are investigated by electrical conductivity relaxation method in this work. At 700 °C, the water incorporation reaction would happen in the formation of both hydration and hydrogenation. The hydration reaction would happen at the sacrifice of oxygen vacancy, and then, the incorporated proton diffuses from outer layer to the inner bulk. But due to much higher chemical diffusion coefficient of proton than oxygen vacancy, the highly mobile protons are charge compensated by holes, instead of waiting for the less mobile oxygen vacancy, and thus causes the speeding increased hole concentration, i.e., increased conductivity. So in the hydration reaction, the decoupled diffusion of proton and oxygen vacancy would result in a non-monotonic conductivity relaxation curve, i.e., twofold diffusion. After that, the proton uptake reaction would transit to hydrogenation, as total decreased conductivity in a monotonic curve. Keywords Proton uptake . Twofold diffusion . Electroneutrality . Protonic ceramic fuel cells
Introduction Protonic ceramic fuel cells (PCFCs) [1, 2] have attracted more and more attention due to their excellent application prospect in low temperature range because of their higher electrolyte ionic conductivity compared with traditional oxygen ion conductors, and lower activation energy [3, 4]. And among lots of key component materials in PCFC, the air electrode materials, especially those with oxygen ionic/protonic/electronic triple conductivity, have presented much more importance [5]. But it is a challenge to find such materials because the behaver of hole and proton even is antagonistically. In present research, BaCo0.4Fe0.4Zr0.1Y0.1O3-δ [6], Ba0.5Sr0.5Fe0.8Zn0.2O3-δ [7], and Ba0.5Sr0.5Co0.8Fe0.2O3-δ-F0.1 [8] were reported with considerable
* Tao Hong [email protected] * Tong Liu [email protected] 1
School of Materials Science and Engineering, Hefei University of Technology, Hefei 230009, China
2
School of Power and Mechanical Engineering, Wuhan University, Wuhan 430072, Hubei, China
proton conductivity and efficient performance when applied in PCFC. And the induced protonic conductivity in mixed conductor is much more difficult since the proton surface uptake and diffusion mechanism in mixed conductor are not clear. And the transport mechanism in triple conductor should be much more complex than that in traditional oxygen ionic/electronic mixed conductors, since the diffusion kinetics for oxygen ion/proton/ hole are different [9]. The wat
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