Metal-Support Interaction between Titanium Oxynitride and Pt Nanoparticles Enables Efficient Low-Pt-Loaded High-Performance Electrodes at Relevant Oxygen Reduction Reaction Current Densities

Armin Hrnjić; Ana Rebeka Kamšek; Lazar Bijelić; Anja Logar; Nik Maselj; Milutin Smiljanić; Jan Trputec; Natan Vovk; Luka Pavko; Francisco Ruiz-Zepeda; Marjan Bele; Primož Jovanovič; Nejc Hodnik

doi:10.1021/acscatal.3c03883

Metal-Support Interaction between Titanium Oxynitride and Pt Nanoparticles Enables Efficient Low-Pt-Loaded High-Performance Electrodes at Relevant Oxygen Reduction Reaction Current Densities

ACS Catal. 2024 Feb 2;14(4):2473-2486. doi: 10.1021/acscatal.3c03883. eCollection 2024 Feb 16.

Authors

Armin Hrnjić^{1

2}, Ana Rebeka Kamšek^{1

3}, Lazar Bijelić^{1

2}, Anja Logar^{1

2}, Nik Maselj^{1

3}, Milutin Smiljanić¹, Jan Trputec^{1

3}, Natan Vovk^{1

3}, Luka Pavko^{1

3}, Francisco Ruiz-Zepeda¹, Marjan Bele¹, Primož Jovanovič¹, Nejc Hodnik^{1

2}

Affiliations

¹ Department of Materials Chemistry, National Institute of Chemistry, Hajdrihova 19, Ljubljana 1000, Slovenia.
² University of Nova Gorica, Vipavska 13, Nova Gorica 5000, Slovenia.
³ Faculty of Chemistry and Chemical Engineering, University of Ljubljana, Večna pot 113, Ljubljana 1000, Slovenia.

Abstract

In the present work, we report on a synergistic relationship between platinum nanoparticles and a titanium oxynitride support (TiO_xN_y/C) in the context of oxygen reduction reaction (ORR) catalysis. As demonstrated herein, this composite configuration results in significantly improved electrocatalytic activity toward the ORR relative to platinum dispersed on carbon support (Pt/C) at high overpotentials. Specifically, the ORR performance was assessed under an elevated mass transport regime using the modified floating electrode configuration, which enabled us to pursue the reaction closer to PEMFC-relevant current densities. A comprehensive investigation attributes the ORR performance increase to a strong interaction between platinum and the TiO_xN_y/C support. In particular, according to the generated strain maps obtained via scanning transmission electron microscopy (STEM), the Pt-TiO_xN_y/C analogue exhibits a more localized strain in Pt nanoparticles in comparison to that in the Pt/C sample. The altered Pt structure could explain the measured ORR activity trend via the d-band theory, which lowers the platinum surface coverage with ORR intermediates. In terms of the Pt particle size effect, our observation presents an anomaly as the Pt-TiO_xN_y/C analogue, despite having almost two times smaller nanoparticles (2.9 nm) compared to the Pt/C benchmark (4.8 nm), manifests higher specific activity. This provides a promising strategy to further lower the Pt loading and increase the ECSA without sacrificing the catalytic activity under fuel cell-relevant potentials. Apart from the ORR, the platinum-TiO_xN_y/C interaction is of a sufficient magnitude not to follow the typical particle size effect also in the context of other reactions such as CO stripping, hydrogen oxidation reaction, and water discharge. The trend for the latter is ascribed to the lower oxophilicity of Pt-based on electrochemical surface coverage analysis. Namely, a lower surface coverage with oxygenated species is found for the Pt-TiO_xN_y/C analogue. Further insights were provided by performing a detailed STEM characterization via the identical location mode (IL-STEM) in particular, via 4DSTEM acquisition. This disclosed that Pt particles are partially encapsulated within a thin layer of TiO_xN_y origin.