+ – AEC
+ – AEM
+ – PEM
+ – SOE
H (plus CO)
Air plus O
O
O
O
H
H
H
-
-
+
-
OH
OH
H
O
H O as water
H O as water
H O as water
Air
H O as water (plus CO )
Anion exchange membrane/alkaline electrolyte membrane (AEM) Cathode: Ni / Ni al loys Anode: Fe, Ni, Co oxides
Polymer electrolyte membrane/proton exchange membrane (PEM/PEMEC)
Alkaline electrolysis cell (AEC)
Solid oxide electrolysis cell (SOE/SOEC)
Cathode: Pt/Pd Anode: lrO 2 i RuO 2
Cathode: Ni, Co or Fe Anode: Ni Lye: 25-30% potassium hydroxide solution in water 100% electrical power
Electrode material
Cathode: Ni Anode: La/Sr/MnO (LSM) or La/Sr/Co/FeO (LSCF) Zirconium oxide with ~8% yttrium oxide ~25% heat from steam, ~75% electrical power Up to 0.5 A/cm 2 Hydrogen (or syngas if fed with steam and CO 2 ) Close to atmospheric ~750 to 850°C
Anion exchange ionomer (e.g. AS-4)
Electrolyte
Fluoropolymer ionomer (e.g. Nation, a DuPont brand) 100% electrical power
100% electrical power
Energy source
0.2-1 A/cm 2 Hydrogen
Up to 3 A/cm 2 Hydrogen Up to 40 bar ~60°C
Up to 0.5 A/cm 2 Hydrogen
Current density Hydrogen or syngas product Gas outlet pressure Cell temperature
Up to 35 bar H 2 , 1 bar 0 2 ~60°C
Up to 40 bar ~80°C
Figure 2 Electrolysis technologies for hydrogen or syngas production
liquid hydrocarbons is through electrolysis. This can be using a solid oxide electrolyser cell (SOEC) system with CO₂ feed to yield syngas, a conventional polymer electrolyte membrane (PEM), or an alkaline electrolyser to make hydrogen and then convert it to hydrocarbons with the addition of CO₂ and further processing. For example, hydrogen and CO₂ can be converted to methanol using a hydrogenation process over copper and zinc-oxide catalysts. Alternatively, the CO₂ can be reduced to carbon monoxide (CO) to form syngas in combination with hydrogen. In the case of electrolysis, significant amounts of electrical power must be consumed. For the process to be carbon neutral, this must be
renewable power from solar, wind, or hydro schemes. Nuclear power is low-carbon, but the debate is open as to whether it is a ‘sustainable’ mode of power generation or not. These are effectively the Scope 1 emissions. For the CO₂ feed to the e-fuels process, implementation of BECCS on major biomass power generation facilities can provide abundant raw material. For example, the Drax power plant, which opened in 1974 in North Yorkshire, is the largest thermal power plant in the UK. It was previously coal-fired and has switched to burning imported wood pellets in recent years. It is still the UK’s largest single CO₂ emitter but is regarded as carbon-neutral because it burns biomass.
www.decarbonisationtechnology.com
41
Powered by FlippingBook