Scientists develop method for producing green hydrogen

Engineers at the University of Illinois at Chicago (UIC) have developed a method for producing hydrogen gas from water, using only solar energy and agricultural waste such as manure or shells. The method reduces the energy required to extract hydrogen from water by 600%, creating opportunities for sustainable production.

Hydrogen-based fuels are one of the most promising sources of clean energy. However, producing pure hydrogen is an energy-intensive process, often requiring coal or natural gas and large amounts of electricity.

In a paper published in the journal Cell Reports Physical Science, a multi-institutional team led by UIC engineer Meenesh Singh reveals the new process for producing green hydrogen.

The method uses a carbon-rich substance called biochar to reduce the amount of electricity needed to convert water into hydrogen. By using renewable energy sources, such as solar or wind power, and capturing byproducts for other uses, the process can reduce greenhouse gas emissions to zero.

Electrolysis, the process of splitting water into hydrogen and oxygen, requires an electrical current. On an industrial scale, fossil fuels are typically required to generate this electricity.

Recently, scientists lowered the voltage required for water splitting by introducing a carbon source to the reaction. However, this process also uses coal or expensive chemicals and releases carbon dioxide as a byproduct.

Singh and his colleagues modified this process to use biomass from common waste products. By mixing sulfuric acid with agricultural waste, animal waste or sewage, they created a paste-like substance called biochar, rich in carbon.

The team experimented with different types of biochar made from sugar cane hulls, hemp waste, waste paper and cow manure. When added to the electrolysis chamber, all biochar varieties reduced the energy required to convert water to hydrogen. The best performance was from cattle manure, which reduced the electrical need by six times to approximately one-fifth of a volt.

The energy requirements were so low that the researchers were able to power the reaction with a standard silicon solar cell generating about 15 milliamps of current at 0,5 volts. This is less than the amount of power produced by an AA battery.

Orochem Technologies Inc., which sponsored the research, has filed patent applications on its biochar and hydrogen production processes, and the UIC team plans to test the methods on a large scale.

The researchers' article received the following summary:

Slow water oxidation reactions limit the electrolysis of water to produce H2, which can be alleviated by using carbon-based materials such as agricultural waste as reducing agents. Biochar from this biomass can reduce the equilibrium potentials of cells under standard conditions from 1,23 V to 0,21 V, avoiding direct water splitting at the anode. However, some challenges impede biochar oxidation, including poor biochar binding, electrode agglomeration, and surface passivation. We found that the improved C/O ratio, crystallinity, and negative zeta potential improve biochar oxidation kinetics at moderate temperatures. Smaller particle sizes and better mixing prevent electrode agglomeration, improving biochar stability. Here, we report sub-volt biochar-coupled H2 production, often referred to as biochar-assisted water electrolysis (BAWE), producing ∼250 mA/gcat H2 current with 100% Faradaic efficiency. Current greater than 1 mA was observed at a cell potential close to the equilibrium cell potential of 0,2 V. Using a single-junction solar cell powered BAWE, ∼15 mA H2 is generated at 1 Sun, resulting in ∼4,8 % solar efficiency for hydrogen, equivalent to ∼35% when the energy of H2 relative to H2O (without biochar) is assumed.

The full text can be read at doi.org/10.1016/j.xcrp.2024.102013