In the realm of alternative energy sources, wind power, hydropower, solar power, and nuclear power have garnered significant attention and investment. However, hydrogen, despite its immense potential, has remained relatively obscure and lacks widespread recognition. But the tides are turning. The November 2021 Shanghai Import Expo disrupted this narrative when Japan's Toyota unveiled the second-generation Mirai hydrogen fuel cell passenger car in China. Boasting an impressive range of 850 kilometers, it surpassed the majority of lithium-powered electric vehicles in a single stride.
Today, "hydrogen-powered vehicles" typically refer to hydrogen fuel cell cars. Unlike lithium-ion batteries, hydrogen fuel cells are devices that generate electrical energy through a chemical reaction between hydrogen and oxygen. The sole byproduct of this reaction is water, setting it apart from conventional fuel vehicles that emit harmful substances like carbon oxides, nitrogen oxides, and sulfur oxides. Consequently, hydrogen is hailed as an energy source capable of achieving "zero emissions."
Titanium plays a vital role in hydrogen fuel cells. Titanium-based bipolar plates within these cells possess thinness, excellent conductivity, favorable thermal properties, high mechanical strength, and efficient gas isolation. These characteristics enhance the power density of the cell. Toyota's MIRAI fuel cell vehicle utilizes titanium bipolar plates. Furthermore, the gas diffusion layer (GDL or PTL), constituting 17% of the electrolyzer's cost, employs high-performance industrial-grade titanium as the anode base material, enabling maximum activity.
The fundamental working principle of hydrogen fuel cells involves hydrogen passing through the catalyst (platinum) at the cell's positive electrode, where it decomposes into electrons and hydrogen ions. The hydrogen ions then traverse a proton exchange membrane to reach the negative electrode, where they react with oxygen to produce water and heat. Simultaneously, electrons flow from the positive electrode through an external circuit to the negative electrode, generating electric energy.
In essence, hydrogen and oxygen combine within the fuel cell, generating electricity and water. The electricity powers the vehicle, while water is the sole byproduct expelled from the vehicle.
From this operational principle, hydrogen fuel cells offer significant advantages:
Firstly, cleanliness: Water is the only byproduct, eliminating carbon dioxide emissions.
Secondly, safety: The electrochemical process powering hydrogen fuel cells reduces the risks of spontaneous combustion or explosions associated with combustion-based systems.
Thirdly, convenience: Hydrogen gas can be compressed, facilitating transportation and storage.
It's worth noting that the fuel cell in hydrogen-powered vehicles differs from traditional chemical batteries. A fuel cell enables an electrochemical reaction between hydrogen and oxygen without combustion, producing water as a byproduct and releasing electrical energy.
In hydrogen fuel cell vehicles, electrical energy is generated instantaneously through the reaction between stored hydrogen and atmospheric oxygen within the fuel cell stack. This distinguishes them from electric vehicles, which store energy from an external grid before utilization. Thus, despite the name "fuel cell" in hydrogen vehicles, their energy release process resembles internal combustion engines (reacting gasoline with external oxygen) more closely than the energy storage process in electric vehicles.
Similar to internal combustion engine vehicles, the most expensive component in a hydrogen fuel cell vehicle is the energy generation device rather than the energy storage device (as seen in electric vehicles, where the battery is the costliest component). Specifically, the fuel cell stack holds this distinction, rather than the hydrogen storage tank.
Due to the relatively high cost of hydrogen fuel cell systems, especially the fuel cell stack, current production costs of hydrogen vehicles exceed those of pure electric vehicles and traditional combustion engine vehicles. This cost factor remains a significant challenge in the development of the hydrogen fuel cell vehicle industry.
