Comprehensive review and future perspectives on the photocatalytic hydrogen production


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Received: 29 March 2019 Revised: 13 June 2019 Accepted article published: 19 June 2019 Published online in Wiley Online Library: 23 July 2019

(wileyonlinelibrary.com) DOI 10.1002/jctb.6123

Comprehensive review and future perspectives
on the photocatalytic hydrogen production
Juan Corredor,a María J Rivero,a Carmen M Rangel,b Frederic Gloaguenc

and Inmaculada Ortiza*

Abstract

Hydrogen represents a renewable energy alternative that may positively contribute to get over the global energy crisis while
at the same time reducing its environmental burden. Overcoming the challenge of reaching this potential could be helped
by careful choice of hydrogen (H2 ) sources. Photocatalytic generation of H2 , although a minor alternative, appears to be a
very good option at the time that liquid wastes are being degraded; therefore, this approach has given rise to an increasing
number of interesting studies. Here, we aim to provide an integrated overview of the different photocatalytic, heterogeneous,
homogeneous and hybrid systems. First, we categorize the units and mechanisms that take part in the photocatalytic process,
and secondly we analyze their role and draw comparative conclusions. Thus, we analyze the role of (i) the electron source to
carry out proton reduction, (ii) the proton source, which can be free protons in the medium or a proton donor compound,
(iii) the catalyst nature and concentration, and (iv) the photosensitizer nature and concentration. We also provide an analysis
of the influence of the solvent, especially in homogenous systems as well as the influence of pH. We provide a comparison
of the photocatalytic performance, highlighting the advantages and disadvantages, of different systems. Thus, this review is,
on the one hand, an update on the state of the art of photocatalytic generation of H2 from a full perspective that integrates
homogeneous, heterogeneous and hybrid systems, and, on the other, a source of useful information for future research.
© 2019 Society of Chemical Industry

Keywords: photocatalytic hydrogen production; homogeneous, heterogeneous and hybrid systems; comparative performance

STATE OF THE ART OF PHOTOCATALYTIC
GENERATION OF HYDROGEN
Increased emissions of greenhouse gases to the atmosphere due
to fossil fuel combustion pose a serious threat to the environment.
Hydrogen (H2 )-based energy comes out as a clean alternative
because its direct combustion does not generate pollutants or
greenhouse gases.1–5 Nowadays, 95% of H2 is obtained by steam
reforming of fossil fuels, mainly methane. This process operates at
high temperatures and pressures, and thus is energy-intensive.6–8

Water (H2 O) electrolysis is one of the most promising H2 produc-
tion alternatives, especially, for storage of surplus electricity; a
variety of commercial electrolysers for large-scale applications is
available on the market.9,10 However, the energy consumption
associated with electrolysis must be significantly reduced before
this process becomes competitive at large scales. Photocatalytic
generation of H2 from organic solutions or H2 O, although con-
sidered a minor source in terms of produced H2 volume, appears
to be a complementary and renewable way for simultaneous H2
generation and wastewater remediation.11–16

In 1972, Fujishima and Honda reported the first heterogeneous
photocatalytic H2 production, HETPHP, by water splitting.

3,17 HET-
PHPs are assisted by a semiconductor that acts as catalyst and
light harvester. Five years later, Lehn et al. (1977) published the
first homogeneous photocatalytic H2 production, HOMPHP, from
triethanolamine (TEOA).18 Typical HOMPHPs involve the use of
an organometallic complex as catalyst and a second organic
or organometalic compound as photosensitizer. More recently,
hybrid photocatalytic H2 production systems, HYBPHPs, have been

developed making use of the system units of both HETPHPs and
HOMPHPs, homogeneous catalysts and heterogeneous photosen-
sitizer semiconductors.19

More recently, interesting reviews have addressed separately
each of the three system categories20–26 but there is no inte-
grated and comparative analysis of the three systems. The present
review provides such an integrated overview of the photocat-
alytic generation of H2 , and the influence of the photocatalytic
units and process variables on H2 production rate and stability.
This comparison has been made in terms of H2 production per
unit time per gram of catalyst (molH2·gcat−1·time−1 ) for HETPHPs,
turnover Frequency (TOF) for HOMPHPs and HYBPHPs, and moles
of H2 per mole of catalyst, turnover number (TON), as defined in
Eqns (1) and (2).

The stability of the photocatalytic system, and the process effi-
ciency are determined through the ‘Quantum Yield’ (QY) and
‘apparent Quantum Yield’ (AQY) Eqns (3) and (4),23–27 as indicators

∗ Correspondence to: I Ortiz, Department of Chemical and Biomolecular Engi-
neering, ETSIIT, University of Cantabria, Avda. de los Castros s/n, 39005, San-
tander, Spain. E-mail: inmaculada.ortiz@unican.es

a Department of Chemical and Biomolecular Engineering, ETSIIT, University of
Cantabria, Santander, Spain

b Laboratório Nacional de Energia e Geologia, Lisbon, Portugal

c UMR 6521, CNRS, Université de Bretagne Occidentale, Brest, France

J Chem Technol Biotechnol 2019; 94: 3049 – 3063 www.soci.org © 2019 Society of Chemical Industry

https://orcid.org/0000-0001-9661-2930
mailto:inmaculada.ortiz@unican.es

	A20_OrtizRangel_JChemTechandBiotech2019