Oxygen Evolution Reaction of Oxide-Based Material with and without Doping in Alkaline Solution
Authors: Matsuzawa Koichi , Sumi Kyogo , Suzuki Ryu , Kuroda Yoshiyuki , Mitsushima Shigenori , Ishihara Akimitsu , Ota Ken-ichiro 
Published: February 2020

Recently, the energy and society of hydrogen have been so much focused in Japan. On Oct. 23, 2018, Hydrogen energy ministerial meeting (H2 EM 2018) was held in Tokyo, Japan with cabinet members and officials from 21 countries, regions, and organizations. In the meeting, “Tokyo Statement” was released as the chairman’s summary, and many presentations were also given by international organizations. At the meeting, several presenters expected technologies of water electrolysis to improve more and more due to core technology to produce hydrogen from renewable energies.
Alkaline water electrolysis (AWE) is the most traditional procedure to produce the hydrogen in the large scale with inexpensive cost. The performance of AWE is very stable for long terms under rated power operations, but it is afraid to perform unstable under fluctuation power operation because the degradation of catalytic activity on Ni anode was observed under potential cycling from our previous reports [1]. In the case of hydrogen production from water electrolysis connecting with renewable energies such as wind and solar power, new anode with high durability against potential cycling should be developed to produce “Green Hydrogen” (CO2-free-hydrogen) [2]. Since zirconium and titanium oxide-based material is stable [3] and both ions have no peaks due to the change of valence number in wide range, we focused on zirconium and titanium oxide-based electrocatalyst and apply to them new anode electrocatalyst of AWE [4]. In this study, the catalytic activity of zirconium and titanium oxide-based electrocatalyst with and without doping for the oxygen evolution reaction (OER) have investigated in the alkaline solution.
We prepared three types of oxide-based electrocatalyst; the ZrO2 on TiO2 (110) with 0.5 mol% of Nb doping (0.5Nb-TiO2(110)) fabricated by the arc plasma deposition (APD) procedure, TiOx rod reduced in lack of oxygen atmosphere, and 1 mol% Zr doped TiOx rod (Zr-TiOx). We used conventional three electrode cell with each sample as working electrode while the reversible hydrogen electrode (RHE) and carbon plate were used as reference and counter electrode to demonstrate the electrochemical measurement. In order to evaluate the OER activity of samples, the slow scan voltammetry was performed from 1.2 to 1.8 V vs. RHE in 7 M KOH solution at 303 K.
Figure 1 shows the Tafel plots of OER on oxide-based electrocatalysts. The results of that on substrate of ZrO2 and previous our study are also shown in this figure. Compared with past result, oxide-based electrocatalysts in this study have obviously higher catalytic activities than that of ZrO2/Zr that was prepared by APD on Zr plate. The Tafel slope of OER on ZrO2/ 0.5Nb-TiO2(110) was 54 mV dec-1 the while the that on the Nb 0.5 mol% doped TiO2 (110) showed 194 mV dec-1. The Tafel slope of OER on ZrO2/ 0.5Nb-TiO2(110) was also smaller than that on ZrO2/Zr that was 70 mV dec-1. In the case of TiOx, the catalytic activity of Zr-TiOx for the OER was higher than that of TiOx. The Tafel slope of OER on TiOx was 77 mV dec-1, and it was smaller than that on Zr-TiOx of 94 mV dec-1. According to results, the ZrO2/0.5Nb-TiO2(110) has the best activity for the OER in this study.
Acknowledgement: This work is partially supported by Toyota Mobility Foundation.
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Figure 1