Pulsed electrolysis for CO2 reduction: Techno-economic perspectives

Summary Pulsed electrolysis has emerged as a promising approach to CO2 reduction, offering a simple method to adjust product selectivity and enhance operational stability. However, conceptually applying the dynamic pulse operation process on a large scale highlights its differences when compared to conventional electrolysis processes, impacting the economic feasibility of the process. We discuss the influence of pulsed electrolysis on surface reaction mechanisms and the simulation of changes at both the continuum and smaller scales through computational modeling. Additionally, we point out considerations for applying pulsed CO2 electrolysis to a large-scale process and assess their economic implications, comparing pulsed electrolysis with constant electrolysis.


Pulsed CO2 electrolysis techno-economic analysis 1) Process modeling
The purpose of this process is to observe the change in ethylene's MSP according to variables (e.g., duty cycle, selectivity, catalyst lifetime) when the power is fixed.Other parameters are fixed based on other CO2 electrolysis techno economic analysis study. 1,2(Table S1) The production rate is calculated under the given conditions, and simulations are conducted using Aspen Plus simulators.Based on the obtained heat and mass balances, an economic evaluation is performed.This modeling and analysis process is conducted based on Na et al. 3 Charge loss=total electrolyzer work*charge loss ratio*(1-duty cycle) (Equation S1) Duty cycle= cathodic length cathodic length+anodic length (Equation S2) In pulsed electrolysis, product is not produced while the anodic potential is applied.Therefore, this must be accounted for in the process model.To address this, the stream coming out of the electrolyzer is split in the simulation to only pass on the amount produced in pulsed electrolysis to the downstream process.The electricity and feed of the electrolyzer are reflected in the operating cost only when the cathodic potential is applied.Additionally, charge loss due to anodic potential is accounted for using (Equation S1).The cost of the pulse generator is reflected as a ratio of the electrolyzer cost, referring to a power supply system that applies a constant voltage.Generally, as the power capacity increases, the proportion of the power supply increases, accounting for 20-40%. 4,5Therefore, assuming the pulse generator price is 20% of the electrolyzer, optimistic and pessimistic scenarios are set at 10% and 30%, respectively.In the downstream process, for the cathode, as ethylene is a gas product, it consists of gas/liquid separation (flash drum) for electrolyte separation, CO2 capture (CCS), and pressure swing adsorption (PSA) for H2 separation.For the anode, there is gas/liquid separation for O2  S1.Process assumptions for Pulsed CO2 electrolyzer, Related to Figure 12.

2) Techno-economic analysis
We provide an example of producing ethylene through pulsed CO2 electrolysis.Chemical stoichiometric numerical simulations are conducted using the production rates calculated via PV-EC calculations.Based on the DOE H2A analysis for the current central, the stack cost is set at $550/kW. 4 The reference electrolyzer operates at 1.75 V and 0.4 A/cm 2 , with an installation factor of 1.12.Using these conditions, the electrolyzer cost is estimated by Na et al. 3 methodology.These values are then utilized for techno-economic analysis, with the framework based on Seider et al. 6 The examples of capital and operating costs are results from base condition pulsed CO2 electrolysis.Additionally, the balance of plant is included in the electrolyzer cost.

<PV-EC calculation>
Actual amount of produced electricity from photovoltaic system (PV power=100 MW): Total required electrolyzer cell area Acell: The production rate of C2H4: Cash flow analysis is performed with a plant lifespan of 25 years, a construction period of 2 years, 7-year MACRS depreciation, a 10% nominal interest rate, and a 40% income tax rate to calculate the net present value (NPV).The MSP of the product is calculated to achieve an NPV of 0. As a result, the MSP of ethylene produced by pulsed CO2 electrolysis under the base conditions is calculated to be $5.53/kg, indicating a considerably high value.In terms of capital cost, the electrolyzer accounts for approximately 70%, followed by the pulse generator at 15%.
Additionally, it can be observed that the proportion of electricity cost relative to static is reduced due to the duty cycle.MEA replacement cost is calculated to be high due to the low catalyst lifespan of 30 days.

Figure S1 .
Figure S1.Change in ethylene MSP, Related to Figure 12.MSP change according to (A) duty cycle and (B) MEA replacement.Blue line represents the pulse optimistic case, the gray line represents the pulse base case.

Figure S2 .
Figure S2.The cost breakdown of each unit to CAPEX and OPEX in terms of ratio, based on pulsed CO2 electrolysis base conditions, Related to Figure 12.

Figure S3 .
Figure S3.Pulsed CO2 electrolysis process flow diagram in Aspen plus, Related to Figure