**Author details**

Consequently, the movement in d*-*band center ought to be ideal in a manner that to balance

band center is optimum for Pt3TM (TM = Fe, Co, Ni) electrocatalysts in such a way that to give high ORR activity as compared to other Pt-TM alloys or pure Pt [45]. Also the uniform dispersion of catalyst particles with appropriate particle size (~3–5 nm) again enhances the

The formation of an atomic charge density and asymmetry in spin density on nitrogen-doped graphene system encourages the charge exchange from the carbon support to the adsorbing

tates the O–O bond and helps for its easy dissociation. In other words nitrogen doping helps for the 4e<sup>−</sup> transfer reaction rather than 2e<sup>−</sup> transfer reaction in ORR reaction [38]. Moreover, the doping of nitrogen atoms into the graphene lattice reinforces the bonding between the catalysts nanoparticles and the support that not just aides in a uniform dispersion of catalyst particles on the carbon support additionally prevents their self-agglomeration during long PEMFC operation [47]. In nitrogen-doped (graphene-MWNT) hybrid structures, the nitro‐ gen doping also increases the electrical conductivity of graphene support materials along with

The gathering of many unique properties of graphene-related 2D nanomaterials such as large surface area, excellent conductivity, good mechanical, and chemical stability along with low cost and accessibility for mass production has opened up a new research area in the field of materials science. Chemical modification of graphene-related materials especially by nitro‐ gen doping and incorporation of Pt and Pt alloys can significantly increase the catalytic activity and durability toward oxygen electro-reduction. Even though the following things need to be investigated in depth forfuture studies such as (a) the exact nature of electrocatalytically active sites facilitating theORRin N-dopedgraphene andorigin oftheir catalytic reactivity, (b) design of facile and large-scale synthesis approaches, for N-doped graphene and their hybrids with metals and alloy nanoparticles. With respect to N-doped graphene synthesis, the technique should be capable of the large incorporation of electrochemically active N functional groups to the support. Regarding N-doped graphene hybrids, the method should ensure the precise tuning of the size, morphology and compositions of electrocatalyst particles for getting high ORR catalytic activity and strong bonding between N-doped support and catalyst nanoparti‐ cles for long-term durability, and (c) investigation of alloying effect of Pt with 3d transition metals (Co, Fe, Ni, Cu, etc.) supported on N-doped graphene towards ORR by DFT model‐

B.P. Vinayan acknowledges the Alexander von Humboldt Foundation for research funding.

blocking species. The shift in *d*-

•–) [25, 46]. This debili‐

the solid adsorption of oxygen and weak adsorption by OH<sup>−</sup>

oxygen molecule and results in the creation of an superoxide ion (O2

ORR activity of the electrocatalysts.

190 Recent Advances in Graphene Research

highly conductive carbon nanotubes [25].

**3. Future outlook and challenges**

ing and electrochemical experiments.

**Acknowledgements**

Bhaghavathi Parambath Vinayan

Address all correspondence to: vinayan.parambath@kit.edu

Helmholtz Institute Ulm for Electrochemical Energy Storage (HIU), Ulm, Germany

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