Daniel Esposito | Converting Sunlight into Storable Solar Fuels

Although the history of solar technology dates back more than 2,000 years, it was not until the mid-20th century that mankind first realized the potential of converting sunlight into electricity. Since that time, the science and engineering behind solar-conversion technologies has led to tremendous improvements in efficiency and cost-effectiveness.

Daniel Esposito
Daniel Esposito
Assistant Professor of Chemical Engineering
—Photo by Jeffrey Schifman

Solar energy is an attractive technology because of its global abundance and scalability. “In one hour, enough energy strikes the earth in the form of sunlight to fulfill all of mankind’s energy needs for an entire year!” exclaims Daniel Esposito, assistant professor of chemical engineering. “No other alternative energy source comes close to producing such large quantities of potentially harvestable energy.”

Energy from sunlight is typically harvested through the application of photovoltaic technology, which produces electricity when exposed to light. However, the primary weakness of conventional solar photovoltaic technologies is the inherently intermittent nature of sunlight. This leads to sporadic electricity production, which often conflicts with society’s relatively constant demand for electricity.

To solve the solar intermittency problem, Esposito’s research explores the ways in which sunlight and water can be converted into hydrogen gas, often referred to as a “solar fuel” when produced by this means. The special type of solar cells used for this process are known as photoelectrochemical (PEC) cells or PEC reactors, which have great potential to transform how solar energy is converted and stored. “Solar fuels can be used to store energy produced by the sun during the day, then converted into electricity with a fuel cell when the sun is not shining,” he explains. “By this means, we can effectively use sunlight to meet our energy needs 24/7, even when it is cloudy or nighttime.”

Successful PEC technologies rely strongly on two types of materials: semiconductors and catalysts. Just as in a conventional solar cell, the semiconductor within the PEC is the light absorber that creates a photovoltage. Meanwhile, the catalytic material uses energy harvested by the semiconductor to efficiently facilitate a chemical reaction such as water splitting for hydrogen production. In the most efficient PEC devices, platinum and iridium serve as catalysts, but the high price and limited supplies of these materials make it crucial to develop low cost, stable, and efficient catalytic materials.

Identifying and incorporating earth-abundant catalytic materials into photoelectrochemical devices is one objective of Esposito’s research. To do so, Esposito is excited about the opportunities to collaborate with colleagues in data science and big data analytics in order to identify more efficient, earth-abundant materials and device structures for solar applications.

“My current studies are deeply involved with those efforts, and seek to further improve the efficiency and durability of electrodes using earth-abundant catalysts while incorporating these electrodes into fully functioning reactor concepts that will be necessary for the commercialization of this technology,” says Esposito.

Prior to joining Columbia Engineering in summer 2014, Esposito was a postdoctoral fellow at the National Institute of Technology (NIST).

BS, Lehigh University, 2006; PhD, University of Delaware, 2012

—by Dave Meyers

500 W. 120th St., Mudd 510, New York, NY 10027    212-854-2993