Platinum Nanostructure/Nitrogen-Doped Carbon Hybrid: Enhancing its Base Media HER/HOR Activity through Bi-functionality of the Catalyst

Manas Kumar Kundu; Tanmay Bhowmik; Ranjit Mishra; Sudip Barman

doi:10.1002/cssc.201800856

Platinum Nanostructure/Nitrogen-Doped Carbon Hybrid: Enhancing its Base Media HER/HOR Activity through Bi-functionality of the Catalyst

ChemSusChem. 2018 Jul 20;11(14):2388-2401. doi: 10.1002/cssc.201800856. Epub 2018 Jul 4.

Authors

Manas Kumar Kundu¹, Tanmay Bhowmik¹, Ranjit Mishra¹, Sudip Barman¹

Affiliation

¹ School of Chemical Sciences, National Institute of Science Education and Research (NISER), Bhubaneswar, HBNI, Orissa-, 751 005, India.

PMID: 29863306
DOI: 10.1002/cssc.201800856

Abstract

The design and synthesis of an active catalyst for the hydrogen evolution reaction/hydrogen oxidation reaction (HER/HOR) are important for the development of hydrogen-based renewable technologies. The synthesis of a hybrid of platinum nanostructures and nitrogen-doped carbon [Pt-(PtO_x )-NSs/C] for HER/HOR applications is reported herein. The HER activity of this Pt-(PtO_x )-NSs/C catalyst is 4 and 6.5 times better than that of commercial Pt/C in acids and bases, respectively. The catalyst exhibits a current density of 10 mA cm^-2 at overpotentials of 5 and 51 mV, with Tafel slopes of 29 and 64 mV dec^-1 in 0.5 m H₂ SO₄ and 0.5 m KOH. This catalyst also showed superior HOR activity at all pH values. The HER/HOR activity of Pt-(PtO_x )-NSs/C and PtO_x -free Pt-nanostructures on carbon (PtNSs/C) catalysts are comparable in acid. The presence of PtO_x in Pt-(PtO_x )-NSs/C makes this Pt catalyst more HER/HOR-active in basic media. The activity of the Pt-(PtO_x )-NSs/C catalyst is fivefold higher than that of the PtNSs/C catalyst in basic medium, although their activity is comparable in acid. The hydrogen-binding energy and oxophilicity are two equivalent descriptors for HER/HOR in basic media. A bifunctional mechanism for the enhanced alkaline HER/HOR activity of the Pt-(PtO_x )-NSs/C catalyst is proposed. In the bifunctional Pt-(PtO_x )-NSs/C catalyst, PtO_x provides an active site for OH^- adsorption to form OH_ads , which reacts with hydrogen intermediate (H_ads ), present at neighbouring Pt sites to form H₂ O; this leads to enhancement of the HOR activity in basic medium. This work may provide an opportunity to develop catalysts for various renewable-energy technologies.

Keywords: carbon; doping; electrochemistry; platinum; supported catalysts.