Solar hydrogen: Better photoelectrodes through flash heating
Date:
April 4, 2022
Source:
Helmholtz-Zentrum Berlin fu"r Materialien und Energie
Summary:
Producing low-cost metal-oxide thin films with high electronic
quality for solar water splitting is not an easy task. Especially
since quality improvements of the upper metal oxide thin films
need thermal processing at high temperatures, which would melt
the underlying glass substrate.
Now, a team has solved this dilemma: A high intensity and rapid
light pulse directly heats the semiconducting metal-oxide thin
film, allowing it to reach the optimal temperature without damaging
the substrate.
FULL STORY ========================================================================== Solar energy can directly drive electrochemical reactions at the surface
of photoelectrodes. Photoelectrodes consist of semiconducting thin
films on transparent conductive-glass substrates that convert light
into electricity.
Most photoelectrochemical studies have focused on water splitting, a thermodynamically uphill reaction that could offer an attractive pathway
for the long-term capture and storage of solar energy by producing
'green' hydrogen.
========================================================================== Metal-oxide thin film photoelectrodes are particularly promising for
these diverse functions. They comprise abundant elements, potentially
offering infinite tunability to achieve the desired properties -- at potentially low costs.
Made from plasma At the HZB Institute for Solar Fuels, several teams
focus on developing such photoelectrodes. The usual method to produce
them is pulsed laser deposition: an intense laser pulse hits a target containing the material and ablates it into a highly energetic plasma
deposited on a substrate.
Quality needs heat Further steps are needed to improve the quality
of the deposited thin film. In particular thermal processing of the
metal-oxide thin-film reduces defects and imperfections. However, this
creates a dilemma: Reducing atomic defects concentration and improvements
in crystalline order of the metal-oxide thin films would require thermal processing temperatures between 850 and 1000 degrees Celsius -- but the
problem is that the glass substrate melts at 550 degrees Celsius.
Flash-heating the thin film Dr. Ronen Gottesman from the HZB Institute
for Solar Fuels has now solved this problem: After deposition, using high-powered lamps, he flash-heats the metal- oxide thin film. This
heats it up to 850 degrees Celsius without melting the underlying glass substrate.
"The heat efficiently reduces structural defects, trap states,
grain boundaries, and phase impurities, which would become more
challenging to mitigate with an increasing number of elements in
the metal-oxides. Therefore, new innovative synthesis approaches are
essential. We have now demonstrated this on photoelectrodes made of
Ta2O5, TiO2, and WO3, which we heated to 850 DEGC without damaging the substrates," says Gottesman.
Record performance for a-SnWO4 The new method was also successful with
a photoelectrode material that is considered a very good candidate for
solar water splitting: a-SnWO4.
Conventional furnace heating leaves behind phase impurities. Rapid thermal processing (RTP) heating improved crystallinity, electronic properties,
and performance, leading to a new record performance of 1 mA/cm2 for
this material, higher by 25% than the previous record.
"This is also interesting for the production of quantum dots or halide perovskites, which are also temperature-sensitive," explains Gottesman.
========================================================================== Story Source: Materials provided by Helmholtz-Zentrum_Berlin_fu"r_Materialien_und_Energie.
Note: Content may be edited for style and length.
========================================================================== Journal Reference:
1. Ronen Gottesman, Isabella Peracchi, Jason L. Gerke, Rowshanak Irani,
Fatwa F. Abdi, Roel van de Krol. Shining a Hot Light on Emerging
Photoabsorber Materials: The Power of Rapid Radiative Heating in
Developing Oxide Thin-Film Photoelectrodes. ACS Energy Letters,
2022; 7 (1): 514 DOI: 10.1021/acsenergylett.1c02220 ==========================================================================
Link to news story:
https://www.sciencedaily.com/releases/2022/04/220404120534.htm
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