Yttrium Copper Titanate as a Highly Efficient Electrocatalyst for Oxygen Reduction Reaction in Fuel Cells, Synthesized via Ultrafast Automatic Flame Technique

Replacing platinum (Pt) metal-based electrocatalysts used in the oxygen reduction reaction (ORR) in fuel cells is an important research topic due to the high cost and scarcity of Pt, which have restricted the commercialization of these clean-energy technologies. The ABO3-type perovskite family of an ACu3Ti4O12 (A = Ca, Y, Bi, and La) polycrystalline material can serve as an alternative electrocatalyst for the ORR in terms of low-cost, activity, and stability. These perovskite materials may be considered the next generation electro-catalyst for the ORR because of their photocatalytic activity and physical and chemical properties capable of containing a wide range of A- and B-site metals. This paper reports the ORR activity of a new Y2/3Cu3Ti4O12 perovskite, synthesized via a rapid and facile automatic flame synthesis technique using rotating disk electrode (RDE) measurements. Y2/3Cu3Ti4O12/C has superior ORR activity, stability, and durability compared to commercial Pt/C. The results presented in this article will provide the future perspectives to research based on ACu3Ti4O12 (A = Ca, Y, Bi, Sm, Cd, and La) perovskite as the next generation electro-catalyst for the ORR in various electrochemical devices, such as fuel cells, metal–air batteries, and electrolysis.

2 CaTiO3 formed 3 . Table S1 compares the precursor and synthetic condition used in the synthesis of pristine Y2/3Cu3Ti4O12 by different routes. In previous work based on chemical synthesis, the impurity phases were only observed in the pristine YCTO, while a single cubic phase in YCTO was obtained in most metal cation-substituted YCTO materials. The incorporation of metal cations into the pristine Y2/3Cu3Ti4O12 stimulates the formation of a cubic phase and controls metal ions diffusion during the sintering process 4 . The single cubic phase of pristine Y2/3Cu3Ti4O12 was formed via direct sintering at 950 C for 15 hrs (see supplementary Fig. S1).
The precursor powder immediately after the flame reaction at room temperature also showed the crystalline phase of metal oxides with a minor phase of YCTO, which revealed better results than the other oxidant fuel-based combustion synthesis requiring multistep and a long duration. The current automatic flame synthesis procedure is revealed the feasibility to the fabrication of other isostructural perovskite.

Supplementary Information S2:
VideoS2: Video of automatic flame synthesis reaction took place in an open air condition to obtain the Y2/3Cu3Ti4O12 precursor. Flame ignition of the metal nitrate of yttrium and copper along with solid TiO2was completed within few seconds (15-20 s). This is a highly exothermic flame reaction. The entire synthetic procedure to obtain Y2/3Cu3Ti4O12 from start to finish was complete within a few minutes.

Supplementary Information S3:
Photographs were taken step-by-step during the automatic flame synthesis reaction of Y2/3Cu3Ti4O12.

Supplementary Information S4:
X-ray photoelectron spectroscopy (XPS) was used to identify the chemical nature of the surface of Y2/3Cu3Ti4O12. Fig. S4 shows the spectral regions of Y 3d, Cu 2p, Ti 2p, and O 1s transitions. In the XPS spectrum of Y3d as shown in Fig. S4(a), two main peaks were observed at 157.6 and 159.4 eV, which were assigned to Y3d5/2 and Y3d3/2, respectively. In Fig. S4 The XPS measurements of YCTO confirmed that the oxidation state of Y is +3, Cu is Cu 2+ /Cu 3+ , and Ti 4+ is +4. This is also supported by the CV results.

Supplementary Information S5:
The energy dispersive X-rays (EDX) and line scan spectra of the powder sample for pristine Y2/3Cu3Ti4O12 were carried out to detect the percentage of elements and their uniform distribution inside the material. The EDX spectrum in Fig. S5(a) clearly shows the presence of Y, Cu, Ti, and O with atomic percentages of 2.41, 11.59, 18.17, and 67.83 %, respectively. The Cu/Y ratio was 4.8. EDX analysis is shown the formation of pristine Y2/3Cu3Ti4O12 approaching stoichiometry without impurities. Fig. S5(b-e) shows the high resolution EDX mapping images of Y, Cu, Ti, and O, which reveal a uniform distribution of all elements in pristine Y2/3Cu3Ti4O12. Furthermore, the EDX line-scan profiles of YCTO material have also been carried out as shown in Fig. S5(g), which also show the existence and uniform distribution of all of Y, Cu, Ti and O elements in the YCTO material. This confirmed that the present auto-flame synthesis is a facile and practical process for obtaining highly pure pristine Y2/3Cu3Ti4O12.

Supplementary Information S6:
The SEM analysis has been carried out before and after electrochemical measurement (see Fig. S6). SEM images of YCTO coated on the GC disk were recorded before as shown in Fig. S6(a) and after the stability test as shown in Fig. S6(b). Even after 10,000 cycles at 10 mV s -1 , there is no distinguishable morphological change was observed, which further confirms their structural robustness of YCTO against repeated cyclability test.