PNNL-13501 - Pacific Northwest National Laboratory

Development of a Low-Cost Photoelectrochemical Device for Hydrogen Production via Water
Splitting by Sunlight
Study Control Number: PN00028/1435
Maciej S. Gutowski, John E. Jaffe, Peter M. Martin, Larry C. Olsen
The future vision for hydrogen is that it will be efficiently produced from renewable energy sources and made available
for widespread use as an energy carrier and fuel. The objective of this project is to develop a low-cost
photoelectrochemical device for hydrogen production via water splitting by sunlight.
Project Description
The purpose of this project is to develop an integrated
low-cost photovoltaic/electrolysis system that produces
hydrogen with a solar to hydrogen efficiency of greater
than 20%. Copper indium diselenide solar cells were
fabricated from substrates supplied by Siemens Solar
Industries. A panel consisting of six of these cells wired
in series was constructed for carrying out electrolysis
studies. An electrochemical cell was constructed that
consisted of two platinum electrodes immersed in an
electrolyte. Hydrogen was produced with an efficiency of
approximately 6%. Modeling calculations were
performed to determine thickness of the cadmium
telluride layer, which will be used in a two-cell tandem
structure with copper indium diselenide, and a literature
search was performed to identify low-cost electrode
materials. Theoretical investigations relevant to high
band gap materials were carried out. In particular,
benchmark calculations were performed for bulk total
energy, lattice constant, sublattice distortion for copper
indium diselenide, equation of state (except copper
indium diselenide), and band structure of ZnS, ZnSe,
ZnTe, CdTe, and copper indium diselenide. Fully relaxed
surface calculations were performed for the nonpolar
(110) and polar (111) surfaces of ZnSe. Calculations on
the copper indium diselenide nonpolar (110) surface with
relaxation but without reconstruction have been
completed. This project advanced our ability to produce
hydrogen via water splitting by sunlight using low-cost
materials.
Introduction
Progress in the production of hydrogen via water splitting
by sunlight has been limited by three factors (Khaselev
and Turner 1998): 1) corrosion of the semiconductors
immersed in aqueous solutions (thermodynamically, the
semiconductors with desired band gaps are
photochemically unstable in water), 2) high voltage
308 FY 2000 Laboratory Directed Research and Development Annual Report
required to dissociate water is not compatible with the
voltage produced by single cells, and 3) high cost of
materials for tandem solar cells that might produce
sufficiently high voltage. To overcome these obstacles,
we suggest three paths. First, we proposed to separate the
electrochemical part from the photovoltaic part to
eliminate the problem of corrosion of semiconductors in
aqueous solutions and to build a (modular but integrated)
photovoltaic/electrolysis device (see Figure 1). Second,
we proposed to develop a low-cost, thin-film solar cell
structure to convert solar to electrical energy to achieve
the required voltage for water splitting and high efficiency
of the solar energy conversion. This tandem solar cell
will be based on a Cu(In,Ga)(Se,S)2 copper indium
diselenide cell provided by Siemens Solar Industries, the
world’s leading thin-film solar cell manufacturer, and will
require development of one additional high-band gap cell.
We will consider cadmium telluride and copper- and
silver-based chalcopyrites as candidate materials for the
second cell. Third, in order to achieve a low-cost system,
materials other than platinum will be investigated for
electrodes of the electrochemical module. The benefit of
our approach is development of a low-cost
photovoltaic/electrolysis system that produces hydrogen
with a solar to hydrogen efficiency of greater than 20%.
Approach
The approach involves experimental and theoretical
studies being conducted in parallel. In order to eliminate
the problem of corrosion of semiconductors in aqueous
environments, we propose to separate the photovoltaic
and electrochemical elements (Figure 1). The voltage
from the photovoltaic module is passed to the electrochemical
module but the interaction of semiconductors
with water is eliminated. The experimental efforts were
focused on constructing a prototype photovoltaic/
electrolysis system. The theoretical efforts were focused
on electronic structure studies of bulk, interface, and
defect issues in the active materials used.