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Studying the ORR activity of platinum-based electrocatalysts is an urgent task in the development of materials for proton-exchange membrane fuel cells. The catalytic ink composition and the formation technique of a thin layer at the RDE play a significant role in studying ORR activity. The use of a polymer ionomer in the catalytic ink provides viscosity as well as proton conductivity. Nafion is widely used as an ionomer for research both at the RDE and in the MEA. The search for ionomers is a priority task in the development of the MEA components to replace Nafion. The study also considers the possibility of using the LF4-SK polymer as an alternative ionomer. The comparative results on the composition and techniques of applying the catalytic layer using LF4-SK and Nafion ionomers are presented, and the influence of the catalytic ink composition on the electrochemical characteristics of commercial platinum–carbon catalysts and a highly efficient platinum catalyst based on an N-doped carbon support is assessed. [ABSTRACT FROM AUTHOR]

The use of platinum-free (Pt) cathode electrocatalysts for oxygen reduction reactions (ORRs) has been significantly studied over the past decade, improving slow reaction mechanisms. For many significant energy conversion and storage technologies, including fuel cells and metal–air batteries, the ORR is a crucial process. These have motivated the development of highly active and long-lasting platinum-free electrocatalysts, which cost less than proton exchange membrane fuel cells (PEMFCs). Researchers have identified a novel, non-precious carbon-based electrocatalyst material as the most effective substitute for platinum (Pt) electrocatalysts. Rich sources, outstanding electrical conductivity, adaptable molecular structures, and environmental compatibility are just a few of its benefits. Additionally, the increased surface area and the simplicity of regulating its structure can significantly improve the electrocatalyst's reactive sites and mass transport. Other benefits include the use of heteroatoms and single or multiple metal atoms, which are capable of acting as extremely effective ORR electrocatalysts. The rapid innovations in non-precious carbon-based nanomaterials in the ORR electrocatalyst field are the main topics of this review. As a result, this review provides an overview of the basic ORR reaction and the mechanism of the active sites in non-precious carbon-based electrocatalysts. Further analysis of the development, performance, and evaluation of these systems is provided in more detail. Furthermore, the significance of doping is highlighted and discussed, which shows how researchers can enhance the properties of electrocatalysts. Finally, this review discusses the existing challenges and expectations for the development of highly efficient and inexpensive electrocatalysts that are linked to crucial technologies in this expanding field. [ABSTRACT FROM AUTHOR]

Sluggish oxygen reduction reaction (ORR) of electrodes is one of the main challenges in fuel cell systems. This study explored the kinetics of the ORR reaction mechanism, which enables us to understand clearly the electrochemical activity of the electrode. In this research, electrocatalysts were synthesized from platinum (Pt) catalyst with multi-walled carbon nanotubes (MWCNTs) coated by three polymers (polybenzimidazole (PBI), sulfonated tetrafluoroethylene (Nafion), and polytetrafluoroethylene (PTFE)) as the supporting materials by the polyol method while hexachloroplatinic acid (H2PtCl6) was used as a catalyst precursor. The oxygen reduction current of the synthesized electrocatalysts increased that endorsed by linear sweep voltammetry (LSV) curves while increasing the rotation rates of the disk electrode. Additionally, MWCNT-PBI-Pt was attributed to the maximum oxygen reduction current densities at −1.45 mA/cm2 while the minimum oxygen reduction current densities of MWCNT-Pt were obtained at −0.96 mAcm2. However, the ring current densities increased steadily from potential 0.6 V to 0.0 V due to their encounter with the hydrogen peroxide species generated by the oxygen reduction reactions. The kinetic limiting current densities (JK) increased gradually with the applied potential from 1.0 V to 0.0 V. It recommends that the ORR consists of a single step that refers to the first-order reaction. In addition, modified MWCNT-supported Pt electrocatalysts exhibited high electrochemically active surface areas (ECSA) at 24.31 m2/g of MWCNT-PBI-Pt, 22.48 m2/g of MWCNT-Nafion-Pt, and 20.85 m2/g of MWCNT-PTFE-Pt, compared to pristine MWCNT-Pt (17.66 m2/g). Therefore, it can be concluded that the additional ionomer phase conducting the ionic species to oxygen reduction in the catalyst layer could be favorable for the ORR reaction. [ABSTRACT FROM AUTHOR]

The combined effect of oxygen and nitrogen functional groups on highly crystalline carbon supports like multiwalled carbon nanotubes (MWCNT) and MWCNT-few layer graphene hybrid structures (MWCNT+FLG) have been investigated towards oxygen reduction reaction (ORR) performance and carbon corrosion durability in polymer electrolyte membrane fuel cell (PEMFC) applications. The pristine carbon supports were modified with oxygen and nitrogen functionalities by treating with concentrated mineral acids and subsequent nitrogen plasma treatment assisted with R.F. magnetron sputtering. Pt nanoparticles were dispersed over these chemically modified carbon supports by polyol reduction method. The physicochemical properties of as synthesized electrocatalysts were studied by different techniques such as XRD, TEM, FTIR, Raman and XPS. Electrochemical properties were investigated by cyclic voltammetry and linear sweep voltammetry in 0.1M HClO4 medium. Compared to commercial Pt/C catalysts, durability show ∼30 % enhancement for the as prepared electrocatalysts due to the presence of large amount of pyrrolic nitrogen and highly oriented graphitic nature of the catalyst supports. The ORR performance were comparable with Pt/C (TEC10E30E) in terms of MSA, 259, 270, 252 A g−1 for Pt/C, Pt/N-f-MWCNT, Pt/N-f-(MWCNT+FLG) respectively. [ABSTRACT FROM AUTHOR]

[Display omitted] • Development in oxygen reduction reaction (ORR) electrocatalysts for fuel cells. • Non-precious metals electrocatalysts with high-electrocatalytic performance. • Carbon-based nanostructures with high surface area and increased active sites for ORR. • Metal-organic framework (MOF) derived electrocatalyst for ORR. • Single atom-based catalysts (SACs) are studied as efficient ORR electrocatalyst. The problem of renewable energy is appealing owing to cumulative power demand, the randomness of the increasing oil costs, and environmental issues. Amongst the numerous renewable energy sources, the fuel cell is acquiring more attractiveness owing to their higher efficiency, cleanliness, and cost-effective supply of power required by the clients. The key issue in the extensive commercial applications of polymer electrolyte membrane fuel cell is the usage of platinum based catalyst that is essentially required for the feasible oxygen reduction reaction. The enhancement of ORR performance, stability, and low cost are the main concerns of the non-precious metals catalyst. This review is focused on the development in non-precious nanomaterial-based electrocatalysts and emphasis to the several kinds of non-noble electrocatalysts with enhanced ORR efficiency. Future prospective and directions are suggested in this review for the further improvement in the strategy to the design and development of highly efficient and low-cost electrocatalyst for polymer electrolyte membrane fuel cells. [ABSTRACT FROM AUTHOR]

Ceria coated carbon nanotubes (CeO 2 @CNTs) were prepared as a versatile support material to improve both the activity and stability of platinum (Pt)-based catalysts. We demonstrated that the CeO 2 nanoparticles (NPs) had an extrinsically remote functionalization effect on the Pt electrocatalysis. The CeO 2 modulated the electronic structure, and facilitated the O 2 adsorption property of Pt without any intrinsic chemical doping or Pt-alloying. This led to d -band electron filling in Pt, and delivery of active oxygens (O−) to the Pt surface via oxygen spillover at the Pt-CeO x interface, thus enhancing the ORR activity. Furthermore, due to the unique redox behavior between Ce3+ and Ce4+, the dissolved Ce ions could also participate in the radical scavenge reaction, which prevents the chemical degradation of polymeric components in the cell. A single cell using the Pt NPs supported on CeO 2 @CNT as a cathode catalyst delivered a superior electrochemical performance and a retained durability compared to the cells with pristine CNT supported Pt NPs. • The ceria functionalized Pt/CNT (Pt@CeO 2 @CNT) was used as PEM fuel cell catalysts. • Ceria improves the ORR activity of adjacent Pt nanoparticles catalyst. • Dissolved Ce ions effectively scavenge the oxidative free radicals. • Pt@CeO 2 @CNT exhibits outstanding activity and stability in PEM fuel cells.. [ABSTRACT FROM AUTHOR]