PhD research sets world record for solar-to-hydrogen efficiency

Even as power grids and passenger vehicles transition to renewable energy, the fact remains that one third the world’s CO2 emission comes from more energy-intensive industries for which a clean energy alternative has yet to emerge.

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Written by: ANU School of Engineering
6 Apr 2022

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Dr Astha Sharma
Dr Astha Sharma

“Direct solar-to-hydrogen is going to change that,” said Dr Astha Sharma, a Research Fellow at the ANU College of Engineering and Computer Science. “Hydrogen has much larger energy content compared to fossil fuels. And hydrogen is an energy carrier, not an energy generator. So, you can store and transport hydrogen energy more efficiently.”

Hydrogen can be produced through electrolysis — the splitting of water into hydrogen and oxygen. “Instead of creating greenhouse gasses, hydrogen energy produces only water, or water vapour, as a by-product when used,” Sharma said.

The problem is that most of the hydrogen being produced today relies heavily on fossil fuels, generating a lot of greenhouse gases. Only 4% is from electrolysis while steam methane reforming and coal gasification make up the rest. And if the electricty that initiates the water splitting process comes from fossil fuels, then electrolysis has a carbon footprint of its own.

“So, our research set out to achieve high performance direct solar hydrogen generation via a low-cost method,” Sharma said. “We use solar energy for water splitting to create and store hydrogen.”

Setting a record, raising the bar

The United States Department of Energy (DOE) had announced a solar-to-hydrogen efficiency standard of 20% — meaning one fifth of the sun’s energy must be converted to hydrogen energy to make the process scalable and economically viable as a replacement for fossil fuels.

Sharma’s PhD research would comprise a team that would be the first to meet that standard, with Dr Fiona Beck, Dr Kylie Catchpole, Dr Siva Karuturi and Dr Heping Shen serving as her PhD supervisors.

They started with the world’s most efficient perovskite-silicon tandem solar cells, which were developed by Dr The Duong and Catchpole. Silicon solar cells have been in use for decades, but the ANU team achieved a world record 26.4% efficiency by adding perovskite to capture bands of the solar spectrum that are not absorbed by silicon.

Sunlight, now converted to electricity, would fuel catalyst-coated electrodes to stimulate the water-splitting process. If 80% of that electricity could be converted to hydrogen energy, they would meet the U.S. DOE standard.

The next piece of the puzzle was to find the right catalyst, which they did using low-cost, earth-abundant materials such as NiMo (nickel-molybdenum) and NiFe (Nickel-Iron), developed in collaboration with UNSW researchers Dr Chuan Zhao and Dr Yuan (Helena) Wang.

A computer simulation developed by Sharma and Beck helped to identify maximum efficiencies and design improvements for semiconductors and catalyst current matching.

The solar hydrogen process they designed met the U.S. DOE standard, and set a world record for solar-to-hydrogen efficiency.

“Because the high efficiency we produced was using a low-cost system, it has provided a pathway towards large-scale renewable hydrogen,” Sharma said.

The global scientific community is “now a step closer” to a renewable energy source that can replace fossil fuels in industries like heavy freight and steel production. The breakthrough has also opened the door to massive economic expansion for Australia.

“It’s a way to export renewable energy around the world,” Sharma said. “Australia is very interested in exporting hydrogen instead of coal. When we do that, we will reduce the carbon footprint of the entire Asian Pacific region.”

Leaving her home to save her home

Sharma grew up in India, where vulnerability to heat waves increased by 15% between 1990 and 2019. Since 2015, drought conditions have plagued 600 million people in India with high-to-extreme water stress, and endangered farming and food production as well.

“That was my first encounter with increasing extreme climate events.” Sharma said. “Growing up, we used to have severe heat wave issues and water scarcity due to drought every few years.”

She recalls that while one region of India was flooding due to heavy rains, other regions were facing droughts. And the frequency of catastrophic climate events seemed to be increasing. She began to make sense of this during high school when she joined an Eco Club, which introduced her to climate change studies.

“I chose to go into renewable energy research as a way to work towards solving the problem,” she said. “From the start, I was intrigued by the idea of working on solar cells.”

She completed her bachelor’s and master’s degrees in Physics at Fergusson College in Pune, India. During that time, she devoured research papers by Beck and Catchpole, recognised world leaders in solar cells.

“That was the thing I was specifically looking for,” Sharma said. “The solar photovoltaic group at the Australian National University is one of the best groups in the world and it was the cutting-edge research they were doing that prompted me to apply here.”

A freak accident delayed her arrival by more than a year. She had been awarded one of India’s most prestigious scholarships and planned to use it to come to ANU to work with Beck for the summer in 2016. Her goal was to distinguish herself during the internship and then apply to the PhD program.

But not long before her day of departure, she ruptured tendons in her ankle while delivering a birthday cake to a friend. She was confined to a bed for months and forced to remain in India for the duration of the scholarship.

But all was not lost. Sharma had made a good impression on Beck while communicating about the ill-fated internship. The following year, Beck invited Sharma to apply to ANU as her PhD student. Sharma was thrilled.

“I thought to myself, Oh, I’m going to get two really great supervisors!” Sharma said, referring to Beck and Catchpole, whose work she had been following for years. “Kylie [Catchpole] was my supervisor’s supervisor [Beck’s] during her PhD.”

Sharma said that before she arrived in Australia, she knew that she would be working on solar hydrogen. Another of her soon-to-be PhD supervisors, Karuturi, “had been working on hydrogen generation since his own PhD days” and had become a world leader on catalyst engineering and integrated systems for direct solar hydrogen generation.

When Sharma arrived in Australia in May of 2017, Karaturi, Beck, and Catchpole were in the process of applying for funding from the Australian Renewable Energy Agency (ARENA) for what would become the Efficient Solar Hydrogen Generation project.

They described the project to Sharma, and suggested that her PhD research should focus on meeting the goals set out in the grant proposal.

In August of 2018, Karaturi, Beck, and Catchpole began work as principal investigators on the Efficient Solar Hydrogen Generation project in partnership with Shenzhen Kohodo Hydrogen Energy and the University of New South Wales.

Sharma became the first student to join the project. Her record-breaking PhD research grew out of it, and, after she received her PhD in October 2021, she was invited to join the project as a Research Fellow.

“I was happy to stay because I want to see it through,” Sharma said. “Rather than just working on something, I want to understand the big picture story, how feasible it is when we are thinking of scaling it up.”

After brushing up on her chemistry to complete her PhD and working closely with researchers at the ANU School of Physics, Sharma is now collaborating with ANU economists to expand on the techno-economic analysis from her PhD.

Like a second family

On 7 February, 2022, Sharma’s family in India gathered to watch via livestream as she donned her cap and gown and crossed the stage at the majestic Llewellyn Hall. She was the first in her family to receive a PhD.

“My parents, sister, grandma and few other relatives watched it at my parents’ place [in Indore],” she said. “My fiancé and his family watched it together in Pune.”

Sharma has not been able to see her family or her fiancé for more than two years.

When she left Indore for her undergraduate studies in Pune, home was only “an overnight bus ride” away, and she returned once a month. After her arrival in Australia, she had planned to return home once a year, and did so in 2018 and 2019. Then the global pandemic made overseas travel all but impossible.

Sharma said she has missed seeing her family, but that even without their presence, her graduation was still a meaningful day for her. Australia opened its borders to international travel a few weeks after the ceremony, and Sharma said she looks forward to a visit from her fiancé, and her mom and dad, “so that they can see where I live, where I work and all those things”.

Sharma has not felt alone or isolated in Australia. “I still had people around who were taking care of me and making sure that I’m okay,” she said.

For starters, her roommate was also from India and also a PhD candidate. They went through many of the same challenges together, like searching for an area of focus that was not already being pursued elsewhere.

“I got a lot of really good career advice from Fiona and Kylie,” Sharma said. “They taught me how to build a professional and personal life simultaneously without burning myself out.”

Karuturi was very supportive as well. “He is aware of the issues women in STEM face,” Sharma said. “And he comes from an Asian background, so, he helped me settle into a new culture and all the new things. All this is apart from the research help, of course. None of it would have been possible without my supervisors and mentors at ANU.”

Beck and Sharma recently co-authored a chapter for The Climate Doomsday Book, a hybrid print-digital device to be exhibited publicly in both Australia and the UK, with a video written by Sharma included in the installation.

Sharma and her colleagues are now in the process of setting up a new lab to continue solar-to-hydrogen research. One of their next steps is to scale up to a fullsize solar panel using the actual sun, rather than a solar simulator. They believe they can increase the efficiency of their process to 25%, which is the goal the U.S. DOE has set for 2025.

Sharma is happy that she chose ANU for her PhD, and is open to staying for the long term.

“It’s not just about the lab or the research, but also about the people around you, the kind of involvement you get, the kind of people you live with,” she said. “I definitely made the right decision in coming here.”

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