Nature
has provided scientists and engineers with tremendous inspirations
and resources to design new materials, architectures, and devices.
Inspired by the transportation of water and ions in trees, a natural
freestanding wood carbon (WC) electrode with vertically well-aligned
channels and pit pores on the channel walls was adopted as a convection-enhanced
electrode for aqueous vanadium redox flow batteries (VRFBs). In addition,
carboxylic groups were introduced on WC via nitric acid treatment
(A-WC) to improve its wettability and electrochemical catalytic activity.
The large specific surface area (542.28 m2 g–1) after functionalization afforded sufficient electrochemical reaction
sites. Negatively charged A-WC with a zeta potential of −50.6
mV provides an extra driving force for the adsorption of vanadium
cations toward the electrode surface. The discharge capacity retention
for the A-WC electrode full cell is 83.58% after 100 cycles at 100
mA cm–2, whereas the WC electrode full cell only
has a capacity retention of 57.21% after 100 cycles at 100 mA cm–2. Moreover, the A-WC electrode has a predominant effect
on the positive side of the VRFB, and it has a voltage efficiency
of 92.10% and an energy efficiency of 88.23% at a current density
of 40 mA cm–2. Notably, the positive half-cell has
a discharge capacity retention of 90.19% after 100 cycles at 100 mA
cm–2. This work opens a new strategy to apply nature-derived
structures and materials in the flow battery field.
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