Influence of TiO2 coverage on activity and stability of Pd-TiO2/MWCNT-supported catalysts used in direct formic acid fuel cells

• Published in: Journal of materials science Vol. 59; no. 16; pp. 6894 - 6915
• Main Authors: Malolepszy, A., Mazurkiewicz-Pawlicka, M., Stobinski, L., Lesiak-Orłowska, B., Mierzwa, B., Kövér, L., Tóth, J., Chang, Yuan Chih
• Format: Journal Article
• Language: English
• Published: New York Springer US 01.04.2024; Springer Nature B.V
• Subjects: Acids; Augers; Carbon; Catalysts; Characterization and Evaluation of Materials; Charge transfer; Chemistry and Materials Science; Classical Mechanics; Crystallites; Crystallography and Scattering Methods; Density; Electron transport; Energy Materials; Formic acid; Fuel cells; Hydrogen; Interfaces; Materials Science; Metal oxides; Multi wall carbon nanotubes; Nanomaterials; Nanoparticles; Oxidation; Oxygen; Palladium; Poisoning; Polymer Sciences; Solid Mechanics; Stability; Titanium dioxide; Toxicity; Valence
• ISSN: 0022-2461; 1573-4803
• DOI: 10.1007/s10853-024-09586-5

Pd and TiO 2 supported on functionalized multiwall carbon nanotubes (f-MWCNTs) catalysts were investigated in formic acid electrooxidation reaction in direct formic acid fuel cell. TiO 2 (5–60 wt.% loading) on f-MWCNTs was deposited using microwave-assisted hydrothermal method. 20 wt.% of Pd was deposited on TiO 2 /f-MWCNTs by reduction of palladium (II) chloride salt with sodium borohydride. Catalysts’ structure and composition were characterized by XRD, STEM, HR-TEM, TGA, XPS/XAES (Pd, Ti, O spectra features, density of valence states, Auger parameters). Average crystallite size of Pd and TiO 2 from XRD (3–4 nm) agrees with those by HR-TEM (3–5 nm). Low TiO 2 coverages (below 32wt.%) show smaller crystallites due to increased surface hydrophilicity, higher amount of TiO 2 oxygen vacancies with attached Pd nanoparticles, increased density of valence states of strong Pd–TiO 2 interface. In contrary, the higher coverages indicate lower amount of Pd–O–Ti, Ti–O–C, Pd–O–C interfaces, with electron charge transfer from TiO 2 to f-MWCNTs, and to Pd. Catalysts activity (40–106 mWmg Pd −1 ) and stability (5–240 h) are enhanced at low TiO 2 coverages (4–8 wt.%) due to a strong Pd-TiO 2 interface on oxygen vacancies, improved electron transport and a high active surface area. Oscillatory self-cleaning mechanism of Pd is due to oxidation by -OH groups (TiO 2 , f-MWCNTs), and hydrogen and CO spillover.