1D Pd-Based Nanomaterials as Efficient Electrocatalysts for Fuel Cells - Low-cost Nanomaterials: Toward Greener and More Efficient Energy Applications - page 317

is also discussed here due to their importance in fuel cells. Finally, a brief conclusion
and an outlook will be given on the future research directions of 1D Pd-based
nanomaterial as efficient electrocatalysts and hydrogen storage materials.

2 One-Dimensional Pd-Based Nanomaterials as Effective
Cathode Electrocatalysts

From the previous studies, the ORR is considered to proceed by the efficient four-
electron pathway or the less efficient two-step pathway, depending on the elec-
trolyte and the catalytic activity of the cathode materials [ 95 ].
A. Direct 4-electron pathway:
In alkaline solutions

O 2 þ 2H 2 O þ 4e ! 4OH ð 1 Þ

Acid solutions.

O 2 þ 4H þ þ 4e ! 2H 2 O ð 2 Þ

B. Peroxide pathway:
In alkaline solutions

O 2 þ H 2 O þ 2e ! HO 2 þ OH

ð 3 Þ

followed by either the further reduction reaction

HO 2 þ H 2 O þ 2e ! 3OH

ð 4 Þ

or the decomposition reaction

2HO 2 ! 2OH þ O 2 ð 5 Þ

In acid solutions

O 2 þ 2H þ þ 2e ! H 2 O 2 ð 6 Þ

followed by either

H 2 O 2 þ 2H þ þ 2e ! 2H 2 O ð 7 Þ

or

2H 2 O 2 ! 2H 2 O þ O 2 ð 8 Þ