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Enhanced chlorine evolution from dimensionally stable anode by heterojunction with Ti and Bi based mixed metal oxide layers prepared from nanoparticle slurry Although the improved CE and EE of RCS generation on (Bi2O3)3(TiO2)7-H, limited stability in anodic environments was noted specifically due to the dissolution of Bi2O3 particles. Figure S6a illustrates the concentrations of Bi and Ti in electrolyte during an accelerated life test at 1000 mA cm−2 operation for the (Bi2O3)3(TiO2)7-H heterojunction anode. Bi2O3 particles were expected to maintain intrinsic properties so as to be vulnerable to anodic potential bias and local acidity from OER, as confirmed by a distinct accumulation of Bi in electrolyte. EDS mapping (Figure S6b-f) after the life test also located intensified signals of Ir on remains with dissolution/detachment of Bi2O3 particles. The concurrent rise of Ti concentration would be associated with detachment of TiO2 nanoparticles along with the collapse of particle aggregation. In summary, decoration of micron-sized Bi2O3 particles on the TiO2 heterojunction brought about limited or even adverse effects both for RCS generation and stability. 3.4. Reactive chlorine generation by IrTaOy/Bi3Ti7Ox heterojunction anodes In order to address the drawbacks of Bi2O3 decoration, this study evaluated two different Bi3Ti7Ox heterojunction layers with more uniform doping of Bi into the TiO2 matrix. For Bi3Ti7Ox-1 anode, titanium glycolate nano-particle slurry was prepared by polyol-mediated synthesis [14], to be mixed with a bismuth citrate solution (Bi:Ti = 3:7) overnight. During this process, Bi3+ was expected to be randomly substituted with Ti4+ in the polyol structure by ligand exchange to form a homogeneous solid mixture during the subsequent thermal decomposition. In addition, a well-established co-precipitation procedure for metal ion doped nano-sized TiO2 colloidal suspension [24] was employed for preparation of Bi3Ti7Ox-2 anode. −2 Under the same spraying procedure, the mass loading of Bi3Ti7Ox-1 layer was far greater (3.20 mg cm ) than Bi3Ti7Ox-2 (0.342 mg cm−2) due to the different precursor viscosity (aqueous versus organic solvent). The SEM images on the horizontal surface of Bi3Ti7Ox anodes (Figure S7) showed rugged morphology without specific grains of Bi2O3. The outer film contained multiple cracks that have been typically found for annealed mixed metal oxide due to the variable thermal expansion coefficients [25]. In addition, XRD profiles (Fig. 4 and S8) for the both Bi3Ti7Ox anodes showed insignificant peaks relevant to Bi2O3. These observations would substantiate homogeneous mixed metal oxide formation by the modified preparation schemes. Besides reflections from Ti substrate, intense signals from rutile TiO2 dominated on Bi3Ti7Ox-2. Insertion of Bi3+ into the TiO2 lattice would distort the crystalline structure to facilitate transformation of anatase to rutile at relatively low annealing temperature (450 °C) [16]. At superimposable locations, by far smaller peaks were noted on Bi3Ti7Ox-1, suggesting predominant amorphous phase. Evidences were presented that polyol-mediated Ti-glycolate could remain amorphous up to 500 °C [14]. CV presented in Figure S9a estimated areal capacitance to be 14.91 mF cm−2 and 21.96 mF cm−2 for Bi3Ti7Ox-1 and −2, respectively. Moderately lower capacitance of Bi3Ti7Ox-1 would be associated with the greater mass loading of outer layer and film resistance. During the LSV in 50 mM NaCl solutions (Figure S9b), anodic current waves on Bi3Ti7Ox anodes outperformed (Bi2O3)3(TiO2)7–H anodes and the voltammogram of Bi3Ti7Ox-1 was comparable with TiO2-H. Despite the lack of conclusive evidence, coordinately unsaturated active sites in amorphous structure (Bi3Ti7Ox-1) could moderately facilitate the kinetics of OER and ClER. Fig. 5 shows that both Bi3Ti7Ox anodes marked CERCS near unity (93.6% and 98.3%, on average). Consequently, the IrTaOy/Bi3Ti7Ox heterojunction anodes marked the highest EERCS (8.02–8.16 mmol Wh−1 at 2.5 V NHE) among the anodes interrogated in this study. These electrodes even outperformed a commercial Ir based DSA (De Nora) which showed lower values of CERCS (40.9% on average) and EERCS (3.1 mmol Wh−1 at 2.5 V NHE) as shown in Figure S10. These results demonstrated https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7539370/?report=printable[10/12/2020 8:49:16 AM]PDF Image | Enhanced chlorine evolution
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