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As of the increasing demand for sustainable energy, alkaline fuel cells (AFCs) are becoming increasingly popular.This fuel cell can not only save energy and reduce carbon, but also has a conversion efficiency of up to 70%, making it the focus of attention of all walks of life.Alkaline fuel cells use hydrogen and pure oxygen as raw materials to generate drinkable water, heat energy and electricity. Since the 1960s, they have been widely used by NASA in Apollo series of missions and space shuttles.
Alkaline fuel cells rely on redox reactions to generate energy through the interaction between hydrogen and oxygen.
The core operating principle of alkaline fuel cells involves the molecular reaction of hydrogen and oxygen.At the negative electrode, hydrogen is oxidized and the reaction is as described below:
H2 + 2OH- ⟶ 2H2O + 2e-
This process produces moisture and releases electrons, which flow to the positive electrode with the external circuit, where it undergoes a reduction reaction with oxygen:
O2 + 2H2O + 4e- ⟶ 4OH-
The entire reaction consumes one oxygen molecule and two hydrogen molecules, producing two water molecules, and simultaneously releases electricity and heat.
The electrolyte of an alkaline fuel cell is usually a saturated aqueous alkaline solution, such as potassium hydroxide (KOH).However, such systems are sensitive to carbon dioxide (CO2).If carbon dioxide is contained in the air, KOH may be converted to potassium carbonate (K2CO3), which affects the performance of fuel cells. Therefore, pure oxygen operation has become a common practice.Although CAD has argued about this, there is no agreement among academics.
Due to the complexity of the process, many researchers understand that the poisoning problem of alkaline fuel cells may be irreversible or recoverable, depending on the situation.
Alkaline fuel cells can be divided into two categories: static electrolytes and flow electrolytes.Static electrolytes usually use asbestos isolation layers with saturated potassium hydroxide, which can be recycled after water is formed.In contrast, flow electrolyte design allows the electrolyte to flow between electrodes, which can better manage water generation and removal.
The advantages of lithium hydroxide system design lies in its low cost and the ability to replace electrolytes, although it is currently mainly operated in a pure oxygen environment.Such a design reduces the cost of material selection because the catalyst required can be used with non-precious metals, and materials such as iron or copper can be effectively utilized.
The electrical efficiency of alkaline fuel cells is generally higher than that of acid electrolyte-based fuel cells, thanks to the advantages they bring to chemistry.
Compared with acidic fuel cells, alkaline fuel cells have better electrochemical kinetics within the operating temperature range (to 90°C).In the use of catalysts, since the alkaline environment can promote oxygen reduction reaction and accelerate fuel oxidation, the demand for catalysts reduces the threshold for selection and reduces production costs.
At present, alkaline fuel cells look quite good in commercial development, and many new products are constantly put into the market to strengthen the application of this technology.For example, some companies have developed a bipolar version of the technology, which has greatly improved performance.This laid the foundation for future applications, such as the first fuel cell-powered ship "Hydra", which uses the AFC system.
In addition, the emergence of solid alkaline fuel cells, using solid anion exchange membranes to replace liquid electrolytes, successfully solved the problem of poisoning, while expanding the safe range of operation, allowing them to effectively use hydrogen-rich carriers, such as liquid urea solutions or metal amine complexes.
However, with the advancement of alkaline fuel cell technology, we also need to reflect on the future of this technology.Can it gain a place in the future renewable energy market and become a more environmentally friendly and efficient energy option?
