Page 134 - Multifunctional Photocatalytic Materials for Energy

120 Multifunctional Photocatalytic Materials for Energy

6.4 Carbon nitride for other energy applications

The dehydrogenation reaction of organic substrate together with carbon nitride opens
up another pathway for hydrogen energy production. Via polycondensation, Wu and
coworkers [82] employed melamine as a small pitch for repairing the amino and cyano
defects that were residuals on the surface of mesoporous carbon nitride. The ninhy-
drin test results revealed that the defects could be effectively repaired after introducing
melamine into the precursor of mesoporous carbon nitride. The remedied carbon nitride
was innovatively applied in the dehydrogenation of 1,4-dihydro-2,6-dimethylpyridine-
3,5-dicarboxylate, which could produce the bioactive compounds. The repaired carbon
nitride showed a H 2 production rate 6.5 times greater than that of unmodified meso-
porous carbon nitride; the corresponding scheme is shown in Fig. 6.6B. In addition to
hydrogen generation, hydrogen storage is also a problem that is receiving major atten-
tion. Nair et al. [85] incorporated palladium into the matrix of carbon nitride and investi-
gated its performance in hydrogen storage. The hydrogen adsorption/desorption studies
demonstrated that the hydrogen storage capacity of Pb-doped carbon nitride achieved
up to 3.4 wt% at 25°C and 4 MPa because of the spillover mechanism, and exhibited
excellent potential as an effective hydrogen storage medium.
In addition to the production and storage of hydrogen energy, the storage of elec-
tric power in Li-ion batteries shows a promising future. To exploit a stable anode
material for Li-ion batteries, Subramaniyam and coworkers [86] constructed a 3D
structure consisting of exfoliated carbon nitride nanosheets and reduced graphene
oxide layers via a hydrothermal method. The obtained sandwiched carbon nitride
−1
composite showed a robust capacity of 970 mAh g after 300 cycles, which was 15-
fold higher than that of pristine g-C 3 N 4 . In a similar work, Tao et al. [87] prepared a
N, P dual-doped carbon fiber/carbon nitride composite and applied it as an anode in
both lithium and sodium ion batteries. For the Li-ion battery, the carbon nitride-based
−1
heterojunction showed excellent activities with reversible capacities of 1030 mAh g
−1
−1
−1
after 1000 cycles at 1 A g and 360 mAh g after 4000 cycles at 10 A g . Moreover,
−1
as an anode for the Na ion battery, the reversible capacities reached 345 mAh g after
−1
−1
−1
380 cycles at 0.1 A g and 110 mAh g after 4000 cycles at 1 A g .
It can be observed that apart from hydrogen evolution reaction, carbon nitride based
catalyst can also be applied into many other energy production reactions. Therefore,
broadening the application of carbon nitride in generating various renewable energy
resources still needs more efforts.
6.5 Conclusion and outlook

This chapter summarized recent developments in employing carbon nitride-based pho-
tocatalysts for alternative energy production, including hydrogen, hydrocarbon fuels,
and batteries. The photocatalytic performance of carbon nitride was found to improve
significantly via tuning polycondensation parameters, copolymerization, fabrication
of nanostructure, doping, hybridizing, and dye-sensitization. Despite the great pro-
gresses in boosting the activities of carbon nitride for energy storage and conversion,