Developments in high rate,high selectivity, Li‐mediated 

nitrogen reduction to ammonia

Dr. Pavel Cherepanov / Dr. Bryan Suryanto

Monash University

Non ‐ Haber‐BoschProcess Flow Diagram

Electrochemical Ammonia Production (ambient T,P)

Power supply

Water

Air

Electrolyser

Air Separation Unit (ASU)

NH3 Separation Unit  NH3 (Ammonia) 

N2

The Challenge:

Nitrogen Reduction reaction (NRR):

N2 + 6H+ + 6e‐ 2NH3  (g) E° = +0.056 V vs. NHE

Competing Hydrogen Evolution Reaction (HER):

2H+ + 2e‐ H2 E° = 0 V vs. RHE

Can we suppress the Hydrogen Evolution Reaction to achieve high selectivity towards N2 to ammonia?

Suryanto et al Nature Catalysis 2019MacFarlane et al Adv Materials 2019

Electrochemical Ammonia Synthesis

Potential Direct Electrochemical Ammonia Production Modalities

“A Roadmap to the Ammonia Economy” Joule (2020)

Li – Mediated Ammonia Synthesis

cathode

e‐

anode

e‐

NH3 B‐

H+

proton source 

Li+ Li(s)  Li3N(s)

Li3N(s) + 3C2H5OH  3Li+ + 3C2H5O‐ + NH3

N2 HBproton carrier 

Constant Current Mode

J. Electroanal. Chem (1994)Selectivity: 42‐60 % (50 bar)

ChemElectroChem (2020)Selectivity: ca. 10% (ambient P)

Joule (2019), Nat. Catal. (2020)Selectivity: ca. 19‐35% (ambient P)

Cell voltage: up to 20 V 

WaterState of the Art: Salt (Mediator):  Li(CF3SO3)   (constant current mode)  Solvent:  (Tetrahydrofuran, THF)

Proton Source:  Ethanol       

0

0.1

0.2

0.3

0.4

0.5

8 16 24 32 40 48 56 64

0

10

20

30

40

50

60

70

80

8 16 24 32 40 48 56 64

Li – Mediated Ammonia Synthesis

Temperature

Pressure

Solvent

Mediator (Salt)

Proton source

Applied Voltage

Cathode materialAnode Material

Water content

Time

H‐conc.

Ref. el.

Stirring

OCP resting

Cycling

OPTIMISATION PARAMETERSFaradaic Efficiency, % (=selectivity)

NH3 formation rate, g m-2 s-1

Experiment run #

Identifying the inherent issues

Since the first report on Li-mediated NRR in 1993, the electrochemical cell has not evolved very much….

• THF is still the typical solvent of choice

• EtOH is still used as a proton source

• Cu as the cathode material

• Pt as the anode material

Electrolyte Engineering

cathode anode

NH3B‐

H+

H2

N2HBproton carrier 

Electrolyte development is the key!

Electrolyte Requirements:

• High ionic conductivity

• Low water solubility (hydrophobic)

• Chemically stable

• Non-sacrificial

e‐ e‐ e‐ e‐ e‐

H2O

H2

MyN

x

0 5 10 15 200

20

40

60

80

100

0

15

30

45

60

NH

3 Yie

ld ra

tes

(g m

-2 h

-1) Faradaic efficiency (%

)

2 ba

r

N2 Pressure (bar)

0

20

40

60

80

100

-1.05 -0.90 -0.75 -0.60 -0.45 -0.30 -0.150

15

30

45

60

75

NH

3 yi

eld

rate

s (g

m-2 h

-1)

Potential vs Li/Li+

Faradaic efficiency (%)

Li-eNRR in the MU-2020 Engineered Electrolyte

MU-2020

Highly conductive electrolyte

30x more conductive than conventional electrolyte

Performance overview

N2 pressure dependence Potential dependence @ 20 bar N2

Average cell voltage (V) 4.0 - 4.8 VMaximum NH3 selectivity (Faradaic efficiency %) 84% ± 11%Maximum NH3 production rate 48 ± 12 g m-2 h-1

0 8 16 24 32 40 48 1192 1200

-14

-12

-10

-8

-6

-4

-2

-25

-20

-15

-10

-5

0

MU-2020 State-of-art electrolyte

Cel

l vol

tage

(V)

Time (min)

Applied current density (mA cm

-2)

Applied current densitySystem overload

Electrochemical stability comparison to the conventional electrolyte

Conventional electrolyte (0.2 M LiBF4 + 0.17 M EtOH in THF)

Current density : 8 mA cm-2

Cell lifetime : 18 minutesCell voltage > 12 VNH3 Yield rate : 8.6 g m-2 h-1

NH3 Selectivity : 47.4%

MU-2020

Current density : 22.5 mA cm-2

Test duration > 1200 minutesCell voltage < 5 VNH3 Yield rate : 43.5 g m-2 h-1

NH3 Selectivity : 92% Energy efficiency : 25%

MU‐2020Conventional electrolyte

ARENA milestones, literature target & performance projection

60 g m-2 h-1

202052019419943Literature – Max EE = 2.8%

Target – Giddey et al (CSIRO)1

Target – DoE REFUEL2

ARENA ProjectOur work – highest recorded: 120 g m-2 h-1

Literature target(Giddey et al)

600 g m-2 h-1

FE = 90%EE = 60%

1 Int. J. Hydrogen Energy, 38, p.145762ARPA-E (2016). REFUEL.3J. Electroanal. Chem. (1994), 367, p. 183 4Joule (2019), 3, p. 11275Nature Catalysis (2020), 3, p. 463

Monash ARENAProject target

6.12x10‐2 6.12x10‐1 6.12x100 6.12x101 6.12x102 6.12x103

NH3 production rate (g m‐2 h‐1)

6 6 66 6 6

Our strategy to reach the DoE’ target for production rate

Development of high specific surface area electrodes •Metal foam•3D printed metal electrodes

Prototyping a 1 kW flow cell

Acknowledgement

The Hydrogen/Ammonia Team