Fuel cells are considered one of the most promising technologies for replacing fossil fuels as energy source in many branches of industry. They use the chemical energy of hydrogen or other fuels to cleanly and efficiently produce electricity. Fuel cells can work with a wide range of fuels and feedstocks and produce power for large systems such as utility power stations. They consist of a negative electrode and a positive electrode placed on both sides of an electrolyte. The fuel is fed to the negative electrode, and air is fed to the positive electrode. One of the most common forms of fuel cells are hydrogen fuel cells. There, a catalyst at the negative electrode separates hydrogen molecules into protons and electrons, which then take different paths to the cathode. The electrons pass through an external circuit, creating a flow of electricity. However, while hydrogen is a very abundant chemical element in the universe, it must be derived from substances, often natural gas and fossil fuels, but also water (“green hydrogen), because it occurs naturally only in compound form with other elements in liquids, gases or solids. The necessary extraction makes the production of hydrogen fuel cells expensive as well as, in the case of fossil fuels, has a negative impact on the environment. Moreover, hydrogen used in fuel cells is a compressed gas, which creates its own set of challenges for storage and transportation. There have been attempts to design fuel cells from other materials too, such as ethanol, which can alleviate some of the problems encountered in hydrogen fuel cells. Ethanol which is made from corn or other agricultural-based feeds, is a liquid and therefore safer and easier to transport than hydrogen.
Now (2022), scientists at the Clemson Nanomaterials Institute (CNI) and their fellow researchers at the Sri Sathya Sai Institute of Higher Learning (SSSIHL) in India have found a method to combine curcumin contained in turmeric and gold nanoparticles to create an electrode which needs much less energy to efficiently convert ethanol into electricity.
The researchers concentrated their studies on the anode of the fuel cell, where the ethanol or other feed source is oxidised. Gold was used as a catalyst. Instead of conducting polymers, metal-organic frameworks, or other complex materials which are commonly employed to deposit the gold on the surface of the electrode, the researchers chose curcumin because of its structural uniqueness. Curcumin was used to decorate the gold nanoparticles and stabilise them by forming a porous network around the nanoparticles. The scientists were able to deposit the curcumin gold nanoparticles on the surface of the electrode at a 100 times lower electric current than in previous studies. They also found that without the curcumin coating, the performance was poor because the gold nanoparticles agglomerated because the surface area exposed to the chemical reaction was reduced. The coating was needed to stabilise the framework and create a porous environment around the nanoparticles.
Replacing expensive platinum as the main constituent of fuel-cell electrodes has long been a chief interest of scientific research. In 2017, scientists designed composites consisting of zinc and cobalt, Zn/Co-N/C and Zn/Co-Fe/N/C, which they had both gained from the single zeolitic imidazolate framework (ZIF) precursor Zn/Co-ZIF containing equivalent quantities of zinc and cobalt metal sites. The composites were produced by pyrolysing the precursor at 700°C in an inert gas atmosphere as such and after mixing it with iron salt and 1,10-phenontraline in ethanol. Catalytic tests for oxygen reduction reaction (ORR) in an electrochemical cell showed good results for potential application in platinum-free catalysts for low temperature fuel cells.
Image: TEM images of Zn/Co-ZIF (A) and Zn/Co-Fe/N/C materials. The scale bar corresponds to 200 nm.
Source: Tatiana Lastovina, Julia Pimonova and Andriy Budnyk/ Platinum-free catalysts for low temperature fuel cells/ Journal of Physics: Conference Series, Volume 829, Applied Nanotechnology and Nanoscience International Conference 2016 (ANNIC 2016) 9–11 November 2016, University Pompeu Fabra (Balmes building), Barcelona, Spain/ doi:10.1088/1742-6596/829/1/012007/ Open Access This article is licensed under a Creative Commons Attribution 3.0 licence
In 2020, scientists created a platinum-free catalyst made of ruthenium and nickel, Ru7Ni3/C, which showed very good hydrogen oxidation reaction activity in rotating disk electrode as well as membrane electrode assembly measurements. The hydrogen oxidation reaction mass activity and specific activity of Ru7Ni3/C in the rotating disk experiments was many times greater than in conventional platinum catalysts. The hydroxide exchange membrane fuel cell with Ru7Ni3/C anode was able to produce a high peak power density and good durability over 100 h of operation. Because of the weakened hydrogen binding of Ru through alloying with Ni and enhanced water adsorption through the presence of surface Ni oxides, a high hydrogen oxidation reaction activity of Ru7Ni3/C was achieved. Using the Ru7Ni3/C catalyst, costs reductions were estimated at 85% less compared to common state-of-the-art platinum catalysts, which made it a highly promising candidate for economical hydroxide exchange membrane fuel cells.
Image: Characterizations of the Ru7Ni3/C catalysts: a Transmission electron microscopy (TEM) image of the as-Ru7Ni3 NPs (scale bar, 100 nm). b TEM image of the Ru7Ni3/C catalyst (scale bars, 100 nm). c The X-ray powder diffraction (XRD) patterns of the as-Ru7Ni3 NPs and Ru7Ni3/C. d High-resolution TEM (HRTEM) images of the Ru7Ni3/C (scale bar, 5 nm). Inset shows the corresponding red box region (scale bar, 1 nm). e High-angle annular dark-field (HAADF) scanning TEM (STEM) image and corresponding energy-dispersive X-ray spectrometry (EDX) mapping showing the distribution of Ru and Ni of a nanoparticle in Ru7Ni3/C (scale bar, 10 nm). f EDX line-scanning profile of a nanoparticle in Ru7Ni3/C. Inset shows the HAADF-STEM image of the corresponding nanoparticle.
Source: Yanrong Xue, Lin Shi, Xuerui Liu, Jinjie Fang, Xingdong Wang, Brian P. Setzler, Wei Zhu, Yushan Yan & Zhongbin Zhuang/ A highly-active, stable and low-cost platinum-free anode catalyst based on RuNi for hydroxide exchange membrane fuel cells/ Nature Communications volume 11, Article number: 5651 (2020), 06 November 2020/ doi.org/10.1038/s41467-020-19413-5/ Open Access This article is licensed under a Attribution 4.0 International (CC BY 4.0)
Designing ethanol fuel cells using gold and turmeric has many advantages: electrodes made from these materials are very efficient. They are not expensive to produce because they do not consist of synthetic polymeric substrates and other elaborate materials. They are also eco-friendly. Moreover, the gold curcumin nanocomposite exhibited excellent stability (~200 cycles), easy electron transfer ability, high catalytic activity, and low activation energy towards electrooxidation of ethanol and methanol in an alkaline medium. Its oxidation kinetics can be compared to those of the gold-polymer composites.
The next step in the research will be to scale up the process and collaborate with an industrial partner who can produce the fuel cells and build stacks of fuel cells for real application. Moreover, the research could not only be significant for the energy industry, but also for other scientific branches: the unique properties of the electrode might be used for future applications in sensors, supercapacitors and the like. In collaboration with the SSSIHL research team, the team of scientists were testing the electrode as a sensor to identify changes in the level of dopamine in urine samples, which might prove useful in the treatment of Parkinson's disease and attention deficit hyperactivity disorder. If everything goes according to plan, a new type of fuel cell will soon be available to promote the energy transition.