SR12 - Product Processing & Biomining

Complete the boxes

What are requirements to capture and purifiy water

• No chem. contamination

• No microbial contamination

• Specific pH range

• Removal of e.g. Cu, Mo, Ag, Cd, Sn, P for PEM electrolysis (to avoid electrode poisoning

Set up the redox-reaction occuring in a H2O-Electrolysis. What is its minimum p.d. ?

What are strengths/results of using zero-gap setup over a classical (Alkaline) electrolysis setup

→ results in larger current densities & higher cell efficiencies

What are the drawbacks of zero-gap setups? How does the dual-membrane approach correct this ?

→ Zero Gap: Maintenance of gas phase seperation by porous electrodes and transport layer

Dual Membrane: Aims to improve gas phase seperation

What is the main difference of a Proton Exchange Membrane (PEM) Electrolysis to a classical Alkaline (liquid) electrolyte ?

→ Employs a polymer electrolyte membrane instead of a liquid electrolyte, operates at higher pressure & higher current density

BUT requires corrosion-resistant iridium or platinum electrodes

Define the term … Reversible Potential (E_rev)

→ Minimum potential to apply between two electrodes to make the water dissociation reaction occur

Define the term … Activation Overpotential at anode and cathode (E_act,an and E_act,cat)

→ Kinetics of the electronic charge transfer reactions

Define the term … Ohmic Overpotential (E_ohm)

→ Caused by non-infinite conductivity of the electrolysis cell

Define the term … Diffusion Overpotential (E_diff)

→ For high current densities, the reaction is no longer controlled by electronic transfer but by matter transfer

Define the term … Bubble Overpotential (E_bub)

→ Increased resistance due to non-conductive bubbles covering parts of the electrodes

What are the characteristics of Solid Oxide Electrolysis (SOE)

• High-temperature process (650-1000°C) that employs a solid electrolyte

• Efficiencies of around 80% achievable

• uses a porous cathode to allow H2O vapour to react to H2 and oxygen ions

• Problem: Anode delamination due to O2 pressure buildup

How do AEL,PEM and SOE differ in terms of charge carrier & transport direction ?

• AEL → Hydroxide ions (OH-) carry the charge from cathode to anode

• PEM → Protons (H+) carry the charge from anode to cathode

• SOE → Oxide ions (O2-) carry the charge from cathode to anode

What is the main problem of H2O-Electrolysis for space application and what countermeasure could be enforced ?

Problem:

• Reduced buoyancy and bubble detachement induces overpotentials due to increased ohmic resistance

Countermeasure:

• Nanopattering

• UV irradiation

• Pressure swings

• Vibration

other issues: Gas-Liquid phase seperation → can be counteracted by centrifugal pumps, porous membranes

What are the characteristics of “Solide Oxide Electrolysis” (SOE) Process for CO2 Electrolysis ?

• Heated CO2 (800°C) flows over the nickel-catalysed cathode surface under an applied electric potential CO2 + 2e- → CO + O²-

• CO and any unreacted CO2 are exhausted through an outlet tube

• O²- ions are electrochem. driven through the solid oxide electrolyte to the anode and combine there to produce the gaseous O2 that is relased from the anode cavity at a rate proportional to the current

What are the risks involved with electrode coking ?

Principal Reactions:

(1) CO2 + electricity → CO + 0.5 O2

(2) CO + electricity → C + 0.5 O2

If carbon is produced it will coat the electrodesm interferring with electrolysis process. Nickel in cathode a well-known catalyst for that

What does the Safe Voltage Zone represent ?

→ Represents Zone of NO electrode coking

What are challenges faced with Biomining in space

• Survival of bacteria in space environment (main factor is radiation)

• Requires Water

What primary bacteria is used for biomining in space ?

Acidithiobacillus ferroxidans uses elementary sulfur, tetrathionate and ferrous iron as electron donors

+able to grow anaerobically

+able to solubilise metals from lunar & martian regolith

What is the correlation between lunar regolith & terrestrial plant growth

→ More mature regolith provides poorer substrate for plant growth than immature regolith (higher surface area, higher nanophase iron content)

On lunar regolith simulants, plantrs grow comparatively well