Activity and Durability of Titanium Oxide-Based Electrocatalyst for Oxygen Evolution Reaction in Alkaline Solution
Authors: Matsuzawa Koichi , Suzuki Ryu , Nozaka Atsushi , Ishihara Akimitsu 
Published: July 2021

On Oct. 14, 2020, Hydrogen energy ministerial meeting (H2 EM 2020) was held by the ministry of economy, trade and industry (METI) of Japanese government as online special event with cabinet members and officials from 23 countries, regions, and organizations. In the meeting, “Global Action Agenda (GAA) Progress Report” was released as the chairman’s summary to share the progress of technical development for hydrogen-based society. In the open session, presenter from industrial company of water electrolysis introduced to improve its technologies for producing hydrogen from renewable energies [1]. In our previous study, the hydrogen producing from renewable energies is called as “Green Hydrogen” [2].
Alkaline water electrolysis (AWE) has already commercialized all over the world and recently applied its system for the Power-to-Gas (PtG) in Europe and Japan such as Fukushima hydrogen energy research field (FH2R). In the FH2R, one of the largest module of AWE has operated from 2020 and this module also introduced in GAA progress report as shown in above. However, it is reported that the degradation of Ni anode shows operating by variable renewable energy (VNE) [3]. From this point of view, the alternative anode with high durability against VNE should be required for green hydrogen production. We focused on titanium oxide-based electrocatalyst (TiOx) and have studied its catalytic activity for oxygen evolution reaction (OER) [4-5]. In this study, we have investigated the activity and durability of TiOx with and without Ni addition for the OER in alkaline solution.
Two types of TiOx with 1 mol% of Ni (Ni-TiOx as shown in the following section) and without addition were prepared under oxygen starvation atmosphere, and then formed as rod shape (φ = 5.0 mm, Toshima manufacturing Co., Ltd.). 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 (SSV) was performed from 1.2 to 2.0 V vs. RHE in 7 M KOH at 303 K. In the case of durability evaluation, the acceleration degradation test (ADT) was demonstrated from 0 to 2.0 V under scan rate of 1 Vs-1 for 20000 cycle, and then SSV was performed as described in above to compared with initial OER activity.
Figure 1 shows Tafel plots of OER on Ti oxide-based electrocatalysts. The results of initial Ni wire and TiOx are also shown in this figure. The current density was based on geometric surface area. According to Ni addition with very small amount, the catalytic activity for the OER on Ti oxide-based electrocatalyst has obviously enhanced, and the Tafel slope of initial OER on Ni-TiOx was 52 mV dec-1 the while the that on the TiOx and Ni wire were 180 and 47 mV dec-1. Moreover, the OER activity of Ni-TiOx after ADT has higher than that of initial Ni-TiOx, and Ni-TiOx does not show the degradation by ADT while the geometric current density at 1.6 V of TiOx after ADT for 5000 cycle was 10% lower than that before ADT. Above all, the Ni addition to Ti oxide based-electrocatalyst has improved for both the catalytic activity for the OER and the durability against VRE.
Acknowledgement: This work is partially supported by Toyota Mobility Foundation.
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Figure 1