Let there be light

Let there be light

9:58 AM, 27th December 2017
Ajay Pisat, Doctoral Candidate, Materials Science and Engineering, Carnegie Mellon University.
Ajay Pisat, Doctoral Candidate, Materials Science and Engineering, Carnegie Mellon University.

In an interview, Ajay Pisat, Doctoral Candidate, Materials Science and Engineering, Carnegie Mellon University with Chemical Today Magazine talks at length about his research on improving the efficiency of photocatalytic water splitting process on perovskite family. 

Advisors: Gregory Rohrer (Department Head and Professor of Materials Science & Engineering) and Paul Salvador (Professor of Materials Science & Engineering) from Carnegie Mellon University.

Research Insight.

My current project broadly focuses on improving the efficiency of the photocatalytic water splitting process. Photocatalysis, in general, means using light to make a chemical reaction happen or speed it up. The photocatalyst absorbs light of a certain energy range and gives this energy to its electrons to make them available for reaction. In this process, electrons want to try to go to the non-excited states. There are six factors to having a good photocatalyst, and my research focuses on two of them. Those are preventing electrons from going back to non-excited states and separating different types of reactions on different areas of the photocatalyst. 

Research benefits.

Most materials which are being researched today for solar water splitting belong to the family of ceramics, and more specifically, to the class of oxides.

I am researching the above phenomena on SrTiO3, which is an archetypal material of the perovskite family of materials. SrTiO3 can absorb only the ultraviolet spectrum of sunlight, which is not an ideal property for efficient photocatalysis. However, it is a very widely studied material and hence, any progress made through our research is envisioned to be applied to other materials of the perovskite family which absorb a broader range of the solar light spectrum. Also, many oxides are very stable for photocatalysis which is an added advantage of this class of materials.

Multiple approaches to improve the process of solar water splitting are being studied all over the world by scientists. My research is just one such approach. However, because it is a study on a mechanism which is material independent to a large extent, it can be applied, in principle, to any material which has favourable attributes for photocatalytic water splitting. This flexibility is the key advantage of my approach.

Hydrogen power applications benefiting from the research.

Given that my research is on improving photocatalysts in general, technology in multiple sectors can be potentially improved. For example, water purification, self-sanitizing surfaces can be improved. If we focus on the hydrogen production aspect, then the power generation sector will have serious competition. There is potential for gridless power ecosystem to develop. By this, I mean that each house will be capable of producing its power requirements on site and hence there will be no need for power transmission lines. Any breakthrough in this field is expected to revolutionize the clean energy sector. This is because compared to solar cells which require batteries to store (which are expensive), solar energy captured as hydrogen can be compressed into gas tanks and stored easily. The initial investment will be considerable but prices should come down eventually, as is the case now with solar cells. Also, agricultural fertilizer which requires hydrogen for its production should benefit. 

Future research plans.

In the future, I would work more on the applied part of photocatalytic hydrogen production, involving material aspects into my research. Also, I plan to build a system based on my current project with favourable materials to quantify the improvement of my process.

Challenges preventing photocatalysis from producing its maximum potential of hydrogen.

 Broadly, the requirements for a good photocatalyst are as follows:

  • Capturing maximum part of the solar spectrum (visible light from 400 to 700 nm)
  • Stable in operation (should not degrade during hydrogen production)
  • Preventing electrons from losing their energy as heat
  • Cost

Even though the requirements are well documented, getting a material which satisfies all of these simultaneously is the barrier to solar hydrogen production.

Comparing the research with ongoing works.

Other groups have made photocatalytic systems which have a reasonable solar-to-hydrogen efficiency but are plagued by problems like cost and instability of materials. Our research is focused on improving inexpensive and stable photocatalysts. Also, the work is complementary to the actual hydrogen production system.

Commercializing the technology.

Commercialization of my research is unlikely because studying the fundamental aspects of photocatalytic hydrogen production through which we envision increase in performance of catalysts by 30 times (maximum).

Research benefits for emerging markets.

Climate change being a global phenomenon, the nature of the economy should not be a factor in the adaptation of this technology (ideally)! However, I believe developed economies have the extra resources to facilitate the change from coal/gas/oil powered energy ecosystems to cleaner hydrogen energy systems. In developing or emerging markets, it is difficult to justify the initial investment cost of setting up the photocatalytic systems to generate hydrogen, convert hydrogen to electricity using generators/fuel cells, and rewire existing infrastructure to engage this electricity when cheaper alternatives utilizing gas and oil exist widely.

Potential research areas for young researchers to explore.

Given that photocatalysis has widespread applications, it would be encouraging to see upcoming researchers translate this physical phenomena into commercially available technology. Hydrogen production through multiple approaches could be looked at:
a) Photobiological hydrogen production – using biological organisms in conjunction with light
b) Photoelectrochemical splitting – converting light to electricity using solar cells and then using the potential difference to split water

Also, utilization of the hydrogen produced has to be possible and efficient too. Hence, hydrogen generators and fuel cells could be researched. Separation of hydrogen and oxygen is a very big issue because the mixture is highly combustible and poses a safety hazard. Researching systems which do this naturally during the water-splitting process will be of immense importance once the production itself has been taken care of.

Challenges faced during the research.

Controlling material composition and characterizing materials at small length scales is one of the major challenges in my research. The length scale at which control is desired is of the order of a few Angstroms (10^-10 meters) to a few hundred nanometers (10^-8 meters). Reliable and reproducible characterization at these length scales is essential for the process to be robust and scalable towards utilizing it on other materials and later, for commercialization.

© Chemical Today Magazine


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