A low-power, tethered, hydrogen lofted dirigible (blimp) for monitoring emergency or environmental conditions. Some example usage cases might be to provide extra "eyes in the sky" in relatively remote locations to lifeguard stations or firemen battling unpredictable wildfires. The airship would need a neutral or low buoyancy hull constructed, perhaps, from an aluminized Mylar party balloon. Hydrogen gas (or even helium), being a small molecule, will slowly leak out of the balloon over long periods of time, so would need to be replenished. (Think of those sad deflated, one-fancy balloons a week after the party.) Unlike helium, sources of hydrogen, such as water, are abundant in our environment. Hydrogen gas may be synthesized by the electrolytic decomposition (or "splitting") of water. The slow leak of hydrogen could, perhaps, be replenished by harnessing the sunlight via solar cells to drive the electrolysis cell, from which the hydrogen gas is collected at the cathode (negative side) and the "waste" pure oxygen is emitted into the atmosphere. This solar-powered lifting gas generating system and control electronics would be anchored on the ground or a floating buoy. A tether, consisting of a lightweight lifting gas transport tube, electrical power, and communication wires would sustain the long-operation of the craft and electronic monitoring systems, while sensor data can be collected and relayed via wireless transmitter onboard the anchor.
An electrical power source is connected to two electrodes, or two plates (typically made from some inert metal such as platinum or stainless steel) which are placed in the water. Hydrogen will appear at the cathode (the negatively charged electrode, where electrons enter the water), and oxygen will appear at the anode (the positively charged electrode). Assuming ideal faradaic efficiency, the amount of hydrogen generated is twice the number of moles of oxygen, and both are proportional to the total electrical charge conducted by the solution. However, in many cells competing side reactions dominate, resulting in different products and less than ideal faradaic efficiency.
Electrolysis of pure water requires excess energy in the form of overpotential to overcome various activation barriers. Without the excess energy the electrolysis of pure water occurs very slowly or not at all. This is in part due to the limited self-ionization of water. Pure water has an electrical conductivity about one millionth that of seawater. Many electrolytic cells may also lack the requisite electrocatalysts. >The efficiency of electrolysis is increased through the addition of an electrolyte (such as a salt, an acid or a base) and the use of electrocatalysts.
Currently the electrolytic process is rarely used in industrial applications since hydrogen can currently be produced more affordably from fossil fuels.[1]
Energy requirements
In order to calculate the energy required to generate enough H2 for a balloon, we'll need to use Faraday's Laws of Electrolysis.
Below is quoted from the wikipedia entry on hydrogen safety:
The flammability limits based on the volume percent of hydrogen in air at 14.7 psia (1 atm, 101 kPa) are 4.0 and 75.0. The flammability limits based on the volume percent of hydrogen in oxygen at 14.7 psia (1 atm, 101 kPa) are 4.0 and 94.0. Explosive limits of hydrogen in air are 18.3 to 59 percent by volume
Flames in and around a collection of pipes or structures can create turbulence that causes a deflagration to evolve into a detonation, even in the absence of gross confinement. (For comparison: Deflagration limit of gasoline in air: 1.4–7.6%; of acetylene in air,[4] 2.5% to 82%)
Background
A low-power, tethered, hydrogen lofted dirigible (blimp) for monitoring emergency or environmental conditions. Some example usage cases might be to provide extra "eyes in the sky" in relatively remote locations to lifeguard stations or firemen battling unpredictable wildfires. The airship would need a neutral or low buoyancy hull constructed, perhaps, from an aluminized Mylar party balloon. Hydrogen gas (or even helium), being a small molecule, will slowly leak out of the balloon over long periods of time, so would need to be replenished. (Think of those sad deflated, one-fancy balloons a week after the party.) Unlike helium, sources of hydrogen, such as water, are abundant in our environment. Hydrogen gas may be synthesized by the electrolytic decomposition (or "splitting") of water. The slow leak of hydrogen could, perhaps, be replenished by harnessing the sunlight via solar cells to drive the electrolysis cell, from which the hydrogen gas is collected at the cathode (negative side) and the "waste" pure oxygen is emitted into the atmosphere. This solar-powered lifting gas generating system and control electronics would be anchored on the ground or a floating buoy. A tether, consisting of a lightweight lifting gas transport tube, electrical power, and communication wires would sustain the long-operation of the craft and electronic monitoring systems, while sensor data can be collected and relayed via wireless transmitter onboard the anchor.
Solar-powered balloons
Hydrogen-based balloons
Electrolysis
In order to calculate the energy required to generate enough H2 for a balloon, we'll need to use Faraday's Laws of Electrolysis.
Energy generation methods
Concerns over H2 Flammability
Below is quoted from the wikipedia entry on hydrogen safety: