Testing Artificial Photosynthesis Systems Using Microfluidics

Researchers at Lawrence Berkeley National Laboratory have developed a testing platform for solar-driven electrochemical systems using microfluidics, which allows small-scale screening of anode and cathode materials for applications like hydrogen generation and water oxidation. The research has been published in Physical Chemistry Chemical Physics (PCCP).

Schematic of a photocatalytic electrochemical system for splitting water into hydrogen and oxygen. The gases can be compressed and stored to use later to generate electricity in fuel cells. Image credit: Berkeley Lab.

In theory, solar power seems like the best way to solve the issue of our increasing demand for energy - it is the single most abundant source of energy on the planet, with enough energy falling on the surface of the earth every hour to power the world for a year.

The problem with this arises when we convert that energy into more useful forms, however - many of the processes we have for using solar energy directly are inefficient, costly, or often both. A huge amount of research effort is beginning to solve these problems in the realm of photovoltaic electricity generation, but relatively little attention has been paid to solar-driven electrochemical processes - often dubbed "artificial photosynthesis" - which could use the sun's energy to generate oxygen and storable fuels like hydrogen and hydrocarbons.

Joel Ager, one of the Berkeley team working at the Joint Center for Artificial Photosynthesis (JCAP) who published their work in PCCP, said:

"The operating principles of artificial photosynthetic systems are similar to redox flow batteries and fuel cells in that charge-carriers need to be transported to electrodes, reactants need to be fed to catalytic centers, products need to be extracted, and ionic transport both from the electrolyte to catalytic centers and across channels needs to occur.

"While there have been a number of artificial photosynthesis demonstrations that have achieved attractive solar to hydrogen conversion efficiencies, relatively few have included all of the operating principles, especially the chemical isolation of the cathode and anode."

As with photovoltaics, nanotechnology is providing a wealth of solutions for researchers investigating the artificial photosynthesis problem. Now the researchers at Berkeley Lab have used the rapidly growing field of microfluidics to create a test-bed for photoelectrochemical systems which might be suitable candidates for industrial scale solar-powered chemical factories, producing fuels from air and water.

The microfluidic system they have designed has a series of parallel microscopic channels, which effectively form the skeleton of an electrochemical cell. These are then connected to various photoelectrocatalyst materials via macroscopic contact points on the outside of the cell.

The products of the parallel electrochemical reactions can be collected separately, so that the performance of the candidate materials can be compared directly.

In this investigation, the JCAP team set up the system for photocatalytic splitting of water into molecular hydrogen and oxygen, but the nature of microfluidics makes the cell highly cusomizable, as lead author Miguel Modestino explains:

"In our experimental realization of the design, a series of 19 parallel channels were fabricated in each device, with a total active area of eight square millimeters. As the microfabricated chips are relatively easy to make, we can readily change dimensions and materials to optimize performance."

The Berkeley Lab's stated mission is to "address the world's most urgent challenges" by tackling issues in materials technology and sustainable energy - this team of researchers are certainly living up to this goal. It seems that this new approach will have a huge impact on this field of research, bringing us ever closer to the goal of complete independence from non-renewable resources.

Source: Testing Artificial Photosynthesis - Berkeley Lab News Center

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