ABSTRACT
Nanomaterials have tremendous implications in various disciplines
of science and technology. The physical, chemical, and electrochem-
ical properties of these materials can be tuned by controlling their
size, shape, surface structure, and compositions (both surface and
bulk) though it is a difficult task at a nanoscale dimension. In
this chapter, nanomaterials, both precious and non-precious metal-
based, relevant to oxygen reduction reaction (ORR) are discussed
after a brief introduction to fuel cells and the mechanism of ORR.
Methods for estimating the ORR product selectivity (H2O/H2O2)
and the electrochemical surface area (ESA) are introduced followed
by the descriptor of activity. The evolution of electrocatalyst from
the unsupported to core-shell structure is presented. These include
precious metal black, carbon-supported alloys of precious metals
(Pt and Pd) with transition metals, shape-controlled, and core-shell
catalysts besides the non-precious metal catalysts. The main focus is
on the chemical synthesis of the above-mentionedmaterials, surface
cleaning, and their activity toward ORR. The origin of the ORR
activity improvement is summarized. The chapter is concluded with
emphasis on the need for further research efforts towards enhancing
the electrocatalytic activity, long-term stability, and reduction of the
cost. Overall, the investigations on ORR significantly contribute to
the better understanding of the electrochemistry of nanomaterials.
Fuel cell is an electrochemical energy conversion device that directly
converts chemical energy of the fuel into electrical energy. The
electrochemical energy conversion process is considered to be very
efficient since it does not involve Carnot efficiency limitations.
Any fuel cell device consists of an anode, where the fuel gets
electrochemically oxidized; a cathode, where the oxidant, air or
oxygen, gets reduced; and an electrolyte that transports the ions
either from the anode to the cathode (cationic electrolytes) or from
the cathode to the anode (anionic electrolytes). Depending on the
type of the ions conducted by the electrolyte medium, fuel cells
operate at low, medium, or high temperature ranges. The low-
temperature fuel cells use proton-conducting polymer electrolyte
membranes (PEMs) or cation exchange membranes as the ion
transport medium. These ion-conducting membranes also function
as a separator between the anode and the cathode avoiding any
short circuit and preventing the direct contact between the fuel and
the oxidant. Among various fuel cells available, low-temperature
fuel cells have attracted significant research attention due to
their possible applications in mobile and transport sectors. Thus,
significant research efforts have been expended on the development
of low-temperature fuel cells.
