Nanowires of Pd and Pd alloys for fuel cell applications: A review of the current state-of-the-art

Pd NPs have emerged as promising candidates to replace Pt since they are one of the most abundant metals in the Pt group, coupled with analogous properties that confer comparable catalytic activity. However, the intrinsic morphology of NPs causes challenges affecting the long-term viability and efficiency of fuel cell (FC) systems, including reduced electrochemical surface area, a profusion of low coordination atoms (LCAs), and susceptibility to dissolution, aggregation, and Ostwald ripening phenomena. Thus, this review addresses two primary strategies to mitigate these challenges: the integration of Pd with more oxophilic elements to form alloys and the morphological transformation of catalysts into nanowires (NWs). The latter strategy can be achieved through diverse methodologies such as hard template or templateless syntheses, chemical vapor or electrochemical depositions, laser-based techniques, self-assembly, and surfactant/surfactantless synthesis. NWs result in catalysts with preferential exposure to highly active crystal facets, a diminished number of LCAs, a high surface aspect ratio, and mass transport resistances. Consequently, NW-based catalysts exhibit enhanced stability and durability within FC systems. This comprehensive review surveys the contemporary applications of Pd and its alloy derivatives in FC systems, covering anode and cathode functions. The analysis is divided into three main sections: (i) the synthesis of Pd-based NWs, (ii) their implementation in anodic applications, and (iii) their use in cathodic contexts. Critical discussions on the addressed research papers are incorporated to highlight their contributions and limitations.