Fabrication of polyoxometalate-modified palladium–nickel/reduced graphene oxide alloy catalysts for enhanced oxygen reduction reaction activity Fereshteh Dehghani Sanij, a Prabhuraj Balakrishnan, a Huaneng Su, a Lindiwe Khotseng b and Qian Xu * a Designing advanced nanocatalysts for effectively catalyzing the oxygen reduction reaction (ORR) is of great importance for practical applications of direct methanol fuel cells (DMFCs). In this work, the reduced graphene oxide (rGO)-supported palladium–nickel (Pd–Ni/rGO) alloy modified by the novel polyoxometalate (POM) with Keggin structure (Pd–Ni/rGO-POM) is efficiently fabricated via an impregnation technique. The physical characterizations such as X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy, inductively coupled plasma optical emission spectroscopy (ICP-OES), field emission scanning electron microscopy coupled with energy dispersive X- ray spectroscopy (FESEM-EDX), and transmission electron microscopy (TEM) are utilized to confirm the structure, morphology, and chemical composition of the fabricated samples. The XRD results verify the formation of the POM-modified Pd 8 Ni 2 /rGO alloy electro-catalyst with the face-centered-cubic (fcc) structure and average crystallite size of 5.54 nm. The electro-catalytic activities of the nanocatalysts towards ORR in alkaline conditions are evaluated by cyclic voltammetry (CV), rotating disk electrode (RDE), and chronoamperometry (CA) analyses. The synthesized Pd 8 Ni 2 /rGO-POM nanomaterial shows remarkably greater ORR catalytic activity and better methanol resistance compared with the Pd 8 Ni 2 /rGO and Pd/rGO electro-catalysts. The promoted ORR activity of the Pd 8 Ni 2 /rGO-POM sample is attributed to the alloying of Pd and Ni components, the uniform scattering of Pd–Ni nanoparticles on rGO, and the alloyed catalyst being modified with POM. Moreover, these findings demonstrate that the resultant Pd 8 Ni 2 /rGO-POM material is attractive as a suitable and cost-effective cathodic catalyst for DMFCs, in which the decorated POMs play a vital role for the enhancement in the catalytic abilities of the nanocatalyst. 1. Introduction Direct methanol fuel cells (DMFCs) have aroused great interest for energy conversion and storage in recent years due to the marked benets, including high efficiency, simple construc- tion, ease of charging, and non-polluting nature. 1–3 Nonethe- less, the practical development of DMFC technologies is hampered by some challenges such as the exorbitant price of platinum (Pt) electro-catalysts, slow kinetics of the oxygen reduction reaction (ORR), and inevitable crossover of methanol through the membrane. 4–6 Hence, developing cost-effective, efficient, and methanol-resistant catalysts for the ORR is of tremendous signicance. In this context, palladium (Pd)-containing electro-catalysts, as attractive potential substitutes, have been actively explored for oxygen reduction in DMFC systems since Pd nanomaterials possess comparatively higher ORR activity compared with that of Pt electro-catalyst, but they are considerably cheaper than platinum. 7,8 Besides, to promote the ORR performance of nanoparticulated Pd catalysts, diverse alloyed materials, alter- native substrates, and modied nanocatalysts have been developed. 9–12 With the continuing growth of nanotechnologies, various investigations have reported that Pd-based alloy mate- rials are becoming appealing nanocatalysts. A variety of alloyed materials like PdCu, 13 PdFe, 8,14,15 PdAg, 16 PdCo, 17,18 and PdAu 19 have been investigated on account of their greater catalytic activity and cost-effectiveness. Pd-containing bimetallic alloyed catalysts, especially Pd–Ni alloys, indicate better electro- catalytic capabilities compared with monometallic systems. 20,21 On the other hand, to enhance the electro-catalytic ability and support the nanocatalysts, different kinds of carbon substrates such as carbon black, 10 carbon nanotubes (CNTs), 22,23 a Institute for Energy Research, Jiangsu University, Zhenjiang 212013, China. E-mail: xuqian@ujs.edu.cn b Department of Chemistry, University of the Western Cape, Cape Town 7535, South Africa Cite this: RSC Adv. , 2021, 11, 39118 Received 16th September 2021 Accepted 29th November 2021 DOI: 10.1039/d1ra06936e rsc.li/rsc-advances 39118 | RSC Adv. , 2021, 11, 39118–39129 © 2021 The Author(s). Published by the Royal Society of Chemistry RSC Advances PAPER Open Access Article. Published on 07 December 2021. Downloaded on 3/5/2022 2:35:09 PM. This article is licensed under a Creative Commons Attribution 3.0 Unported Licence. View Article Online View Journal | View Issue