Electrochemical Compression
Yunho Hwang, Reinhard Radermacher
Center for Environmental Energy Engineering
Department of Mechanical Engineering
University of MarylandCollege Park, MD 20742-3035

IEA HPT US Workshop at NIST, USA, November 12, 2019

Mechanical Compressors
Advantage:

Disadvantage:• Cost effective• Highly efficient• Highly reliable• Noise andvibration• Need forlubrication oil• Hard for cooling40

Dynamic

Centrifugal

Positive
Displacement

fixedmoving

20
0

Reciprocating

Rolling Piston

(20)
(40)
(60)

(40)

(20)

020

4060

2-Turn Rectangular Scroll Compressor
2

Axial

IEA HPT US Workshop at NIST, USA, November 12, 2019

ScrollScrew

Eletrochemical Compression• Electrochemical compression (EC) is a way to compress gas
through electrochemical reactions instead of moving
mechanical parts.
• The compressor configuration is proposed based on the ion
exchange membrane used in fuel cells.
• Works with natural, low-GWP and zero-ODP refrigerants
including hydrogen, water, carbon dioxide, and ammonia• Potential for efficient, oil less, noiseless, and vibration-freecompression for use in air conditioning, refrigeration andpower generation
3IEA HPT US Workshop at NIST, USA, November 12, 2019

CO2 EC Working Principle
Under external electric field, CO2
reacts with O2 and H2O on
cathode to form HCO3-/CO32• Highly selective catalyst
effectively absorb both CO2 andO2• Anion exchange membrane (AEM)
transfers HCO3-/CO32• CO2 and O2 reform at anode withhigher pressure• O2 can be separated by either
storage electrode, or throughphase separation•AnodeCathode• Pt based catalyst facilitates reaction with H2O,
CO2 and O2suction side: 𝑂2 + 2𝐻2 𝑂 + 4𝑒 − → 4𝑂𝐻−
4𝑂𝐻− + 4𝐶𝑂2 → 4𝐻𝐶𝑂3−• CaRuO3 based catalyst facilitates reaction with
CO2 and O2suction side: 2𝐶𝑂2 + 𝑂2 + 4𝑒 − → 2𝐶𝑂32−
4IEA HPT US Workshop at NIST, USA, November 12, 2019

CO2 EC Prototype
Stainless SteelAnion Exchange
Membrane and Carbon
Cloth Electrodes

Discharge Side Gas
Distribution Channel

CO2 EC Prototype• Stainless steel prevents corrosion caused by oxygen• Reduced cost by switching from graphite to stainless steel• Mechanically more durable
5IEA HPT US Workshop at NIST, USA, November 12, 2019

CO2 EC Test Facility

6IEA HPT US Workshop at NIST, USA, November 12, 2019

CO2 EC Discharge Side Gas Composition
Catalyst

Pt MEA
2 mg/cm2CaRuO3MEA
2 mg/cm2

Voltage CO2 Flowcharge [V] [sccm]
1.2
1.2
1.2
1.2
1.2
1.2
1.2
1.2

50
50
50
50
50
50
50
50

O2 Flow[sccm]
5050
50
50
50
50
50
50

Discharge side gas
composition
CO2O2
concentration concentration

0.88
0.73
0.88
0.61
0.88
0.86
0.89
0.88

0.24
0.21
0.23
0.41
0.44
0.44
0.4
0.4

−Pt catalyst EC discharge side: 𝟒𝑯𝑪𝑶−
𝟑 → 𝟒𝑪𝑶2+𝟒𝑶𝑯
𝟒𝑶𝑯− → 𝑶𝟐 + 𝟐𝑯𝟐 𝑶 + 𝟒𝒆−−CaRuO3 catalyst EC discharge side: 𝟐𝑪𝑶𝟐−
𝟑 → 𝟐𝑪𝑶2+𝑶2+𝟒𝒆7

IEA HPT US Workshop at NIST, USA, November 12, 2019

Concentrationratio
3.2
3.4
3.8
3.9
2.1
2.0
2.2
2.2

CO2 EC Compression Ratio••8

EC is operated under highvoltage
Highest compression ratio is 5.6,
at suction condition of 101 kPa(1 atm)IEA HPT US Workshop at NIST, USA, November 12, 2019

Advantages and Challenges

9Advantages

Challenges

EC generally appears to be more
efficient at high pressure ratios

Necessity for precious metals in
MEA catalyst layers

High pressure ratios have beenreportedDifficult to separate carrier gas
from working fluid

EC is likely better at rejecting heatthan mechanical compressor

Very large membrane area
requirements for high flow rates

IEA HPT US Workshop at NIST, USA, November 12, 2019

Conclusions• Eletrochemical compression is emerging from H2 compression.
• EC compression mechanisms for CO2 and NH3 were proposedand experimentally verified.
• Achieved compression ratios of 3 to 5.6• More material and experimental researches needed todetermine EC performance map and reliability• Challenges of EC in vapor compression cycle need more
researches

10IEA HPT US Workshop at NIST, USA, November 12, 2019

11IEA HPT US Workshop at NIST, USA, November 12, 2019Acknowledgement
I gratefully acknowledge the support of the Center for
Environmental Energy Engineering (CEEE) at theUniversity of Maryland.

12IEA HPT US Workshop at NIST, USA, November 12, 2019