1. Communication and dissemination
Three articles with contributions from the AdIrCAT project will be published on international famous journals . Currently, one article is under review, one is submitted and one is in preparation as shown in the report. Also, part of this work has been present in INL annual research symposium and INL research open day.
2. The physicochemical characterization of the catalysts
The surface chemical information of Ru3.4MnOx RuOx and c-RuO2 catalysts are next investigated by XPS and XAFS in Figure 3. As shown in Table 1, more oxygen vacancies exist in Ru3.4MnOx than RuOx and c-RuO2. Significantly, the variation in the proportion of surface oxygen vacancy species and lattice oxygen (OV/OL) is observed from 0.66 to 0.76 after Mn doping, signifying an abundance of OV and thus excellent electronic capture and transfer properties of the nanosheets. The Ru 3p XPS spectrum of catalysts (Figure 3b) exhibits two predominant peaks located at 462.4 eV (Ru4+ species) and 464.5 eV (Ru3+ species). The integrated area of the Ru3+/Ru4+ signals is then calculated to examine the relative abundance of Ru3+ in the different catalysts. The larger value of the ratio of Ru3+/Ru4+ from Ru3.4MnOx than c-RuO2 indicates abundant three valence Ru generates when use NaCl as template.
As shown in the Normalized Ru K-edge XANES of Figure 3c, the absorption edge of Ru3.4MnOx is at slightly lower energy than that of c-RuO2, suggesting a slightly lower Ru valence state in Ru3.4MnOx. An average oxidation state of Ru species in Ru3.4MnOx was approximately +3.3 (Figure 3d), which is considered as the combination of pristine Ru4+ and Ru3+ cation. In the meantime, the presence of Ru3+ and VO defects is also found in the undoped RuOx catalyst, seemly caused by the catalyst synthesis method used NaCl as template. Thus, it can conclude that the Mn doping, in addition to the catalysis synthesis method, has induced the generation of VO defects and more low-valence Ru3+ specie, both of which would impact the activity and durability of Ru3.4MnOx for acidic OER.
3. The OER catalytic performance of catalysts
As shown in Figure 4a, the current density of Ru3.4MnOx is the largest at corresponding potentials among all catalysts and only require 193 mV overpotential to reach a current density of 10 mA cm-2, which is comparable, even superior to other reported catalysts. Obviously, the activity of Ru3.4MnOx is much higher than that of RuOx, indicating the promotional effect of the incorporation of Mn in Figure 4a. The mass activity of Ru3.4MnOx is 1636 A/g at a voltage of 1.5V 17 times larger than c-RuO2 in Figure 4b. Moreover, the Tafel slope of Ru3.4MnOx nanosheets are ≈59 mV dec−1 lower than those of RuOx (69 mV dec−1), and even the benchmark c-RuO2 (104 mV dec−1) (Fig. 3c). Such a low Tafel slope value signies the fast kinetic merit of Ru3.4MnOx for water oxidation. The electrochemical stability is evaluated by galvanostatic electrocatalysis. Obviously, Ru3.4MnOx maintains almost unchanged performance to the initial state for 700 h at a constant current density of 10 mA cm−2, superior to commercial RuO2 (it degrades totally in 0.5 h, Figure 4d).
4. The DFT calculation
The DFT calculations will be performed on the computer cluster with 160 cores available at the host institution using periodic, spin-polarized DFT as implemented in the Vienna ab initio program package (VASP). Based on the calculations, the optimal structure facilitating the OER will be identified and compared to the atomic structures of the catalysts obtained by HAADF-STEM (on-going).
