Splitting water is a two-step process, and in a new study, researchers have performed one of these steps (reduction) with
100% efficiency. The results shatter the previous record of 60% for hydrogen production with visible light, and
emphasize that future research should focus on the other step (oxidation) in order to realize practical overall water
splitting. The main application of splitting water into its components of oxygen and hydrogen is that the hydrogen can
then be used to deliver energy to fuel cells for powering vehicles and electronic devices.
work shows that it is possible to obtain a perfect 100% photon-to-hydrogen production efficiency, under visible
light illumination, for the photocatalytic water splitting reduction half-reaction. These results shatter the previous
benchmarks for all systems, and leave little to no room for improvement for this particular half-reaction. With a stable
system and a turnover frequency of 360,000 moles of hydrogen per hour per mole of catalyst, the potential here is real."
When an H2O molecule splits apart, the three atoms don't simply separate from each other. The full reaction requires
two H2O molecules to begin with, and then proceeds by two separate half-reactions. In the oxidation half-reaction, four
individual hydrogen atoms are produced along with an O2 molecule (which is discarded). In the reduction half-reaction,
the four hydrogen atoms are paired up into two H2 molecules by adding electrons, which produces the useful form of
hydrogen: H2 gas.
The 100% efficiency refers to the photon-to-hydrogen conversion efficiency, and it means that virtually all of the photons
that reach the photocatalyst generate an electron, and every two electrons produce one H2 molecule. At 100% yield, the
half-reaction produces about 100 H2 molecules per second (or one every 10 milliseconds) on each nanorod, and a
typical sample contains about 600 trillion nanorods.
One of the keys to achieving the perfect efficiency was identifying the bottleneck of the process, which was the need to
quickly separate the electrons and holes (the vacant places in the semiconductor left after the electrons leave), and
remove the holes from the photocatalyst. To improve the charge separation, the researchers redesigned the nanorods to
have just one platinum catalyst instead of two. The researchers found that the efficiency increased from 58.5% with two
platinum catalysts to 100% with only one.
Going forward, the researchers plan to further improve the system. The current demonstration requires a very high pH,
but such strong basic conditions are not always ideal in practice. Another concern is that the cadmium sulfide (CdS)
used in the nanorod becomes corroded under prolonged light exposure in pure water. The researchers are already
addressing these challenges with the goal to realize practical solar-to-fuel technology in the future.
published by: Philip Kalisman, Yifat Nakibli, and Lilac Amrivan
for paper published click here
100% efficiency. The results shatter the previous record of 60% for hydrogen production with visible light, and
emphasize that future research should focus on the other step (oxidation) in order to realize practical overall water
splitting. The main application of splitting water into its components of oxygen and hydrogen is that the hydrogen can
then be used to deliver energy to fuel cells for powering vehicles and electronic devices.
work shows that it is possible to obtain a perfect 100% photon-to-hydrogen production efficiency, under visible
light illumination, for the photocatalytic water splitting reduction half-reaction. These results shatter the previous
benchmarks for all systems, and leave little to no room for improvement for this particular half-reaction. With a stable
system and a turnover frequency of 360,000 moles of hydrogen per hour per mole of catalyst, the potential here is real."
When an H2O molecule splits apart, the three atoms don't simply separate from each other. The full reaction requires
two H2O molecules to begin with, and then proceeds by two separate half-reactions. In the oxidation half-reaction, four
individual hydrogen atoms are produced along with an O2 molecule (which is discarded). In the reduction half-reaction,
the four hydrogen atoms are paired up into two H2 molecules by adding electrons, which produces the useful form of
hydrogen: H2 gas.
The 100% efficiency refers to the photon-to-hydrogen conversion efficiency, and it means that virtually all of the photons
that reach the photocatalyst generate an electron, and every two electrons produce one H2 molecule. At 100% yield, the
half-reaction produces about 100 H2 molecules per second (or one every 10 milliseconds) on each nanorod, and a
typical sample contains about 600 trillion nanorods.
One of the keys to achieving the perfect efficiency was identifying the bottleneck of the process, which was the need to
quickly separate the electrons and holes (the vacant places in the semiconductor left after the electrons leave), and
remove the holes from the photocatalyst. To improve the charge separation, the researchers redesigned the nanorods to
have just one platinum catalyst instead of two. The researchers found that the efficiency increased from 58.5% with two
platinum catalysts to 100% with only one.
Going forward, the researchers plan to further improve the system. The current demonstration requires a very high pH,
but such strong basic conditions are not always ideal in practice. Another concern is that the cadmium sulfide (CdS)
used in the nanorod becomes corroded under prolonged light exposure in pure water. The researchers are already
addressing these challenges with the goal to realize practical solar-to-fuel technology in the future.
published by: Philip Kalisman, Yifat Nakibli, and Lilac Amrivan
for paper published click here