Counter Electrode Separation in Electrochemistry: A Practical Guide to Divided Cells

Your platinum counter electrode is dissolving. Your glassy carbon CE is generating CO. And both of these things are reaching your working electrode. We covered the mechanisms behind this in a previous article. If you have not read it, that is the right starting point.

This article is about what to do about it. The answer, in most cases, is physical separation of the counter electrode compartment. Here is when it is necessary, what type of separation to use, and which standard divided electrochemical cells are available for it.

When Counter Electrode Separation Is Not Optional

The contamination risk depends entirely on what reaction is happening at the counter electrode. In a three-electrode setup, the CE potential adjusts spontaneously to pass the same current as the working electrode. When the WE performs a reductive reaction — HER, ORR, CO₂RR — the CE must perform an oxidation.

In inert-gas-saturated electrolyte, the most accessible anodic reactions are OER and, depending on the CE material, Pt dissolution or carbon oxidation to CO and CO₂. These processes generate species — dissolved Pt²⁺, CO, carbon particles — that migrate through the electrolyte and reach the working electrode.

Cui and Sheng (ACS Catalysis, 2023, DOI: 10.1021/acscatal.2c05145) demonstrated this with ICP-MS measurements: in N₂-saturated electrolyte with an unseparated Pt CE, dissolved Pt redeposits on the working electrode and artificially enhances its apparent HER activity. In H₂-saturated electrolyte — where the CE can drive HOR at ~0 V vs. RHE instead — Pt concentration in the electrolyte remains below the detection limit. But in inert-atmosphere conditions, there is no clean alternative anodic reaction available at the CE, and separation becomes the only reliable solution.

The practical rule:

Reaction at WE	Atmosphere	Separation needed?
HER, ORR, CO₂RR	Inert gas (N₂, Ar)	Yes
HER	H₂-saturated, Pt CE ≥10× WE area	Generally no
OER, organic oxidation	Any	Generally no
Corrosion (standard setup)	Any	Usually no

For CO₂RR specifically, separation is also standard practice in three-electrode configurations because the strongly negative cathode potential drives the CE to particularly high anodic potentials. Hika and Woldu (Discover Applied Sciences, 2021, DOI: 10.1007/s42452-021-04796-x) confirmed that Pt CE contamination influences product selectivity in CO₂RR on gold, with dissolved Pt redepositing on the catalyst surface and altering the reaction pathway.

What Type of Separation to Use

The barrier between compartments needs to maintain ionic conductivity while slowing the diffusion of dissolved contaminants. Three main options exist:

• Glass frit is the most straightforward choice for standard aqueous electrocatalysis. Jerkiewicz (ACS Catalysis, 2022, DOI: 10.1021/acscatal.1c06040) recommends it explicitly over Nafion when a Pt CE is used, noting that Nafion membranes are not fully effective at blocking Pt²⁺ migration. Frit porosity is a trade-off: finer pores reduce diffusion more effectively but add ionic resistance.
• Ion exchange membranes — Nafion for acidic media, anion exchange membranes for alkaline — are standard for CO₂RR configurations and setups where separating anolyte from catholyte is also required for product analysis.
• PTFE or ceramic diaphragms appear in cells designed for strongly alkaline or organic solvent systems where glass or Nafion may not be compatible.

One important nuance: separation does not eliminate the CE contamination problem, it contains it. Dissolved Pt or CO accumulates in the CE compartment rather than reaching the WE. The CE itself still undergoes the same reactions — which matters in long-duration experiments or when electrolyte purity needs to be tracked.

Divided Cells Available on ElectroSeek

The following standard cells include built-in CE compartment separation and are available directly through the platform.

H-cell and two-compartment format

The BE H-Cell 50 mL is a straightforward two-compartment H-cell format for standard aqueous experiments where a compact separated configuration is needed without additional features.

The 2-CEC 50 mL Two-compartment Electrochemical Cell is a compact gas-tight two-compartment cell with a built-in CE compartment, glass/PEEK construction, compatible with organic electrolytes.

The H-Cell with Membrane Holder provides 50 mL per compartment with gas-tight fittings and a membrane holder, adaptable to different membrane types depending on the application.

The H-Cell with Glass Frit Separator uses a porous glass frit (4–5 µm) as the separation element — the directly recommended configuration when a Pt CE is used and glass frit is preferred over ion exchange membrane.

The Electrochemical H-Cell is a general-purpose two-compartment option for standard aqueous electrochemistry applications.

Membrane-separated CE — standard three-electrode format

The Standard Electrochemical Dual Holder Cell includes a dedicated membrane-separated CE compartment in a 350–1000 mL glass/PEEK body, compatible with aqueous and organic electrolytes. Available in jacketed version for temperature-controlled experiments.

The Standard Electrochemical Triple Holder Cell separates both the CE and RE compartments from the working electrode solution. Relevant when the reference electrode filling solution — typically KCl from an Ag/AgCl RE — could also contaminate the working electrolyte, for example in chloride-sensitive reactions or non-aqueous systems. Also available jacketed.

A Note on the Reference Electrode

In some cases the RE compartment also needs isolation — not only the CE. Ag/AgCl reference electrodes introduce chloride through the junction frit into the working solution. In non-aqueous systems, chloride-sensitive reactions, or when working with catalysts where even trace chloride affects activity, this matters. The Triple Holder Cell above addresses this.

We will cover reference electrode isolation — and when a pseudo-reference is acceptable — in a future article. Subscribe to the newsletter if you want to be notified when it is published.

The counter electrode is not inert, and what happens in its compartment reaches your working electrode. The structural fix — a divided cell with a glass frit or membrane — is available as standard equipment. No custom fabrication required.

If you are unsure which configuration fits your experiment or need custom solution, feel free to reach out. We will help you identify the right cell for your setup, free of charge.