H2 gNanotechnologies / Materials

10

Environmental remediation, Disinfection, Energy production

Fig. 22061218
Photoirradiation time (h)240Time change in the amounts of H2 prosunlight irradiation (λ >420 nm) (H2 is contin

Sunlight-driven photocatalytic production of H2 from H2O2

selectivity is almost constant).
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Division of Chemical Engineering/Research Center for Solar Energy Chemistry, Graduate school of Engineering Science
Associate Professor Yasuhiro Shiraishi
Researchmap https://researchmap.jp/read0054695▍ Significance of the research and Future perspective
Energy carriers are considered to be the key material for realizing a non-fossil fuel dependent society. H2O2 is a promising candidate but cannot be used for H2 generation. H2O2, therefore, hasbeen considered to be unusable as a hydrogen carrier. Our results
indicated that the use of H3PO4 and an inexpensive metal-free photocatalyst facilitates H2 generation by sunlight. Although it is essential to improve the selectivity and H2 production activity, the results
open a new possibility towards sustainable energy society using
H2O2 as a hydrogen/energy carrier.

Hhv

O6

H2O2–H3PO4 complex

e–H+g-C3N4

H 2 O2VB

H 2 O2h+0V③H+ reduction
2H+ + 2e– → H2

1.14 V ④H2O2 reduction
H2O2 + H+ + e– → H2O + •OH
H2O2 + 2H+ + 2e– → H2O
1.76 V. 1 Mechanism for H2 generation from H2O2 (H3PO4 stabilizes H2O2 by hydrogen
Fig. 1FigMechanism
for H2 generation from H2O2 (H3PO4 stabilizes H2O2 by hybonding interaction with H2O2 and suppresses the reduction by excited electrons)
drogenbonding interaction with H2O2 and suppresses the reduction by excitedelectrons)
362341202061218
光照射時間 (h)24064H2 selectivity (%)= percent H2 generated out of H2O2 decomposed

For the social implementation of H2O2 as an energy carrier, it
is indispensable also to use it as a hydrogen carrier. That is, as
shown in Fig. 1, the on-site generation of H2 from H2O2 (H2O2 → H2+ O2, ΔGº = + 131 kJ mol–1, equation (1)) is necessary. However,
the reduction of H2O2 (H2O2 + H+ + e– → H2O + • OH, H2O2 + 2H+ +2e– → H2O, equation ④) proceeds in preference to the H+ reduction (equation ③) Furthermore, typical metal/metal oxide semiconductor, when used as a photocatalyst, promotes the decompositionof H2O2 on the surface (H2O2 → H2O + 1/2O2, ΔGº = –117 kJ mol–1,equation ⑤). Therefore, there has been no example of generating
H2 from an H2O2 solution.
We made a meta-free photocatalyst consisting of graphitic carbon nitride (g-C3N4) organic semiconductor and graphene quantum dots (GQDs) cocatalysts. We found that sunlight (visible light)
irradiation of an H2O2 solution containing the catalyst and phosphoric acid (H3PO4) successfully produces H2 (Fig. 2). The metal-free catalyst scarcely promote the H2O2 decomposition (equation⑤), and the hydrogen bonding interaction between H 2O 2 andH3PO4 forms a stabilized complex (Fig. 1, right) to suppress theH2O2 reduction(equation ④), thus promoting H+ reduction (equation ③). H3PO4 has long been added to commercially available
aqueous H2O2 solutions as a stabilizer. Therefore, the H2O2 solution
containing H3PO4 obtained after the reaction can be stored andtransported and can be used for on-site H2 generation on an inexpensive metal-free photocatalyst. This may open a new possibility
for the use of H2O2 as a new hydrogen/energy carrier.

GQDe–

H 2 O2②H2O2 oxidation
H2O2 + 2h+ → O2 + 2H+PH

H2 選択率 (%)= 分解されたH2O2のうち生成したH2の割合

Nanotechnologies / Materials▍

Background & Results

H 2 O2CB

0.68 VHOCBV vs NHEOOO⑤ H2O2 decomposition
H2O2 → H2O + 1/2O2(ΔG° = –117 kJ mol–1)H2 生成量 (μmol)

Hydrogen peroxide (H2O2) is an important chemical used forbleaching and disinfection, and is a promising energy carrier as afuel for fuel cell power generation. It is, however, difficult to generate hydrogen gas (H2), and has been considered not to be used asa hydrogen carrier. In this research, we succeeded in generating
H2 from H2O2 by adding phosphoric acid (H3PO4) and a metal-freepowder photocatalyst to an H2O2 solution under sunlight irradiation.
Social implementation can be expected toward the realization of a
new energy society with H2O2 as a hydrogen/energy carrier.

HO①H2 generation from H2O2
H2O2 → H2 + O2 (ΔG° = +131 kJ mol–1)

H2 generated (μmol)

Abstract

図 2 疑似太陽光照射（λ >420nm）による照射時間と H2 生成量および H2 選択率の関係（H2は光照射にともない継続的に生成し、H2 選択率もほぼ一定である）

10206
1218
Photoirradiation time (h)240Fig.
Fig2. Time
2 Tchange
ime cinhathengamounts
e in theofaHm2 oproduced
unts ofandH2 theproHd2 uselectivity
ced and the H2during simulated sunlight irradiation (λ >420 nm) (H2 is continuously generatedselectivitybysu
photoirradiation,nlight irradand
iatHio2 n(λ >4is2almost0 nmconstant).
) (H is continuously generated
2

selectivity is almost constant).
１2. ご自身の顔写真のご提供

P a t e n t Japanese Patent No. 6765132
Shiraishi, Yasuhiro; Takii, Takahiro et al. Resorcinol-Formaldehyde Resins as Metal-Free Semiconductor Photocatalysts for Solar-to-Hydrogen Peroxide
Energy Conversion. Nat. Mater. 2019; 18(9): 985-993. doi: 10.1038/s41563-019-0398-0
Tr e a t i s e
Shiraishi, Yasuhiro; Ueda, Yuki et al. Photocatalytic Hydrogen Peroxide Splitting on Metal-Free Powders assisted by Phosphoric Acid as a Stabilizer, Nat.
Commun. 2020; 11(1): 3386. doi: 10.1038/s41467-020-17216-2
UR
L https://resou.osaka-u.ac.jp/ja/research/2020/20200707_1
K e y w o r d photocatalyst, sunlight, hydrogen peroxide