Issue 4, 2024

Hydrogen storage as liquid solar fuels

Abstract

Because hydrogen (H2) is an explosive gas and the volumetric energy density is quite low, it is highly desired to develop liquid or solid solar fuels as safe hydrogen storage alternatives. This review article focuses on catalytic interconversion between hydrogen and liquid or solid solar fuels using metal complexes as redox catalysts. The first candidate of a liquid solar fuel is formic acid (HCOOH), which is liquid at room temperature and has a fairly high volumetric density of 1.22 g cm−3. HCOOH is produced by hydrogenation of CO2 by H2 with various metal complex catalysts under mild conditions. HCOOH thus produced is used as a fuel in direct HCOOH fuel cells. Hydrogen peroxide that is produced from the catalytic reaction of H2 with O2 is used as a fuel in formate-peroxide fuel cells as well as direct H2O2 fuel cells. Cyclic alkanes and N-heterocyclic species have also been used as liquid organic hydrogen carriers (LOHCs) which can liberate H2 on demand using dehydrogenation catalysts and photocatalysts under photoirradiation, because dehydrogenation of organic molecules to release H2 is an uphill process. LOHCs are also used as fuels in direct liquid fuel cells (DLFCs). On the other hand, plastoquinol is used as an effective hydrogen carrier in natural photosynthesis. In the artificial system, hydroquinones (plastoquinol analogues) are much safer and easier to handle for storage as well as transportation, because hydroquinones unlike H2 are nonflammable and nontoxic and can be safely stored in liquids or as solids. Hydroquinones are produced by photocatalytic reduction of p-benzoquinones with water using a molecular functional model of photosystem II in photosynthesis. Hydrogen is produced by photocatalytic oxidation of hydroquinones using a molecular functional model of photosystem I in photosynthesis. In addition, direct hydroquinone/quinone fuel cells have been developed using anthrahydroquinone-2,7-disulfonic acid (AQDS) as an LOHC.

Graphical abstract: Hydrogen storage as liquid solar fuels

Article information

Article type
Review Article
Submitted
30 ⴽⵜⵓ 2023
Accepted
05 ⴷⵓⵊ 2023
First published
07 ⴷⵓⵊ 2023

Inorg. Chem. Front., 2024,11, 981-997

Hydrogen storage as liquid solar fuels

Y. H. Hong, Y. Lee, W. Nam and S. Fukuzumi, Inorg. Chem. Front., 2024, 11, 981 DOI: 10.1039/D3QI02239K

To request permission to reproduce material from this article, please go to the Copyright Clearance Center request page.

If you are an author contributing to an RSC publication, you do not need to request permission provided correct acknowledgement is given.

If you are the author of this article, you do not need to request permission to reproduce figures and diagrams provided correct acknowledgement is given. If you want to reproduce the whole article in a third-party publication (excluding your thesis/dissertation for which permission is not required) please go to the Copyright Clearance Center request page.

Read more about how to correctly acknowledge RSC content.

Social activity

Spotlight

Advertisements