This behavior strongly suggests that your electrochemical cell is hitting a limit, either of the instrument or the cell itself, which prevents the potentiostat from controlling the potential as programmed. Let’s break down the possible causes and solutions in detail.

Core Problem: Loss of Potential Control

The heart of the issue is that your potentiostat is losing its ability to control the potential across the two electrodes. In a two-electrode setup, the potentiostat applies a current (I) between the working electrode (WE) and the counter electrode (CE) and measures the resulting voltage difference (E=EWE−ECE​). To sweep the potential from 1.4V to 1.5V, it must carefully adjust the current.

When you see the voltage suddenly jump to the maximum value (the “compliance voltage” of your instrument, ~3V in your case), it means the potentiostat is trying to apply the required current to reach the next potential step in the sweep, but it can’t. The system’s impedance becomes so low (or the required current becomes so high) that the instrument maxes out its current output. Even at maximum current, it can’t achieve the target potential, and the voltage reading shoots up to the system’s limit.

Most Likely Causes and Detailed Solutions

Here are the most probable reasons for this behavior, especially in a zinc-air battery system.

1. You Are Not in the Non-Faradaic Region

This is the most likely culprit. The potential window you’ve selected, 1.4V to 1.5V, is very likely NOT a non-faradaic region for a zinc-air battery. It is, in fact, the region where significant faradaic reactions occur.

• What is a Non-Faradaic Region? This is a potential range where no electron-transfer (redox) reactions happen at the electrode surface. The only current flowing should be the non-faradaic “capacitive current,” which is due to the charging and discharging of the electrical double-layer at the electrode-electrolyte interface. This current is typically very small. On a CV plot, this region looks like a flat, featureless rectangle with very low current.
• What Happens in a Zinc-Air Battery?The standard potential (E0) for the overall reaction (2Zn+O2→2ZnO) is around 1.65V. The practical open-circuit voltage (OCV) is typically around 1.35V to 1.45V. When you apply a potential above the OCV, you are charging the battery. The relevant reactions are the Oxygen Evolution Reaction (OER) at the air electrode and Zinc deposition at the zinc electrode. OER: 4OH−→O2+2H2O+4e− (in alkaline electrolyte) The OER has a high overpotential and typically begins in earnest around 1.4-1.5V vs. Zn/ZnO.
• Your Experiment: By sweeping from 1.4V to 1.5V, you are pushing the system deep into the OER region. This is a vigorous faradaic reaction that consumes a massive amount of current. Your potentiostat tries to supply this current to raise the potential, hits its maximum current limit, and loses control. The E vs. t curve shows exactly this: the potential is stable until it hits the OER onset, at which point the current demand becomes infinite from the potentiostat’s perspective, and the voltage reading jumps to the rail.

Solution:

2. Scan Rate is Too High

Even in a quasi-non-faradaic region, a very high scan rate can lead to large capacitive currents (Ic=Cdl×(dV/dt)​). If your scan rate is too high (e.g., >100 mV/s), the required capacitive current might still exceed the limits of your potentiostat, especially if your electrode has a very high surface area.

Solution:

• Start with a low scan rate (e.g., 5, 10, 20 mV/s).
• For non-faradaic capacitance measurements, you typically perform CVs at multiple scan rates (e.g., 10, 20, 40, 60, 80, 100 mV/s) and plot the current vs. scan rate. This plot should be a straight line, the slope of which is related to the capacitance. If your instrument can’t handle 100 mV/s, use a lower range.

3. Instrument Settings (Compliance Limits)

Your potentiostat has safety limits for current and voltage to protect itself and the cell.

• Current Range/Compliance Current: The potentiostat might be set to a low current range. When the massive OER current starts to flow, it immediately hits this limit.
• Compliance Voltage: As mentioned, ~3V sounds like a compliance voltage limit. This is the maximum voltage the instrument’s amplifier can output.

Solution:

• Check your software settings. There is often a parameter for “Max Current” or “Current Range”. For investigating a faradaic process like OER, you would need to set this to a high value (e.g., 100 mA or 1A, depending on your cell).
• HOWEVER, for your stated goal of non-faradaic analysis, you should NOT increase the current limit. Instead, you should fix the potential window (Problem #1) so that the current stays naturally low. Increasing the current limit while scanning in the faradaic region will just pump huge currents into your cell, potentially damaging the electrodes or electrolyte, and it won’t give you the non-faradaic data you want.

4. Cell Assembly and Connections (Less Likely but Possible)

A poor connection or an internal short-circuit could cause abnormally high currents.

• Poor Connection: A loose cable (especially the sense leads if you were using a 4-probe setup, which you aren’t in a 2-electrode system) can cause erratic readings.
• Internal Short: If your zinc electrode and air electrode are touching, or if a zinc dendrite has grown to short the cell, the resistance would be near zero. The potentiostat would try to apply a voltage, see a massive current flow, and immediately hit its limit.

Solution:

• Double-check that all your cable connections to the EC-cell are tight and making good contact.
• Disassemble and inspect your cell. Look for any signs of short-circuiting. Ensure the separator is properly placed and intact.

Summary and Recommended Action Plan

Here is a step-by-step plan to solve your problem:

By following these steps, you will be correctly measuring the non-faradaic response of your system, and the issue of the voltage sweep going to 3V should be resolved. The key takeaway is that the potential window must be chosen based on the actual electrochemical behavior of your specific cell, not on arbitrary values.

Thank you so much, sir, for your valuable answer and an elaborate explanation.

I will implement it and get back to you.

thank you once again

Hello sir

I tried even at after reaching 1.8V it stopped because it sweep to higher current and voltage. i tried to do with 1.37V to 1.39V as my ocv is 1.38V, even it stops due to high current and voltage.

Let’s break down the problem in detail, explore the likely causes, and outline a systematic troubleshooting plan.

Understanding the Core Problem: Voltage Overload due to Current Overload

What you are observing is a protective feature of your potentiostat. Here is the sequence of events:

The E vs. t plot confirms this: you see the potential tracking correctly up to a point (e.g., 1.38V or 1.5V), and then it suddenly shoots up to 3V. The root cause is not the voltage control itself, but an unexpectedly high current demand from your cell.

Why is Your Cell Drawing So Much Current?

You are trying to measure in the “non-Faradaic region,” which should, by definition, have very low current (dominated by double-layer capacitance). The fact that you’re seeing huge currents indicates that you are, in fact, triggering a very strong Faradaic reaction.

Here are the most likely reasons for this in a Zinc-Air battery system:

1. Misinterpretation of the “Non-Faradaic” Window (Most Likely Cause)

• OCV is the Point of Zero Net Current: The Open Circuit Voltage (OCV) of ~1.38V is the potential where the rate of oxidation equals the rate of reduction. It is the thermodynamic equilibrium potential.
• Any Deviation from OCV is Faradaic: As soon as you apply a potential different from the OCV, you are driving a Faradaic reaction.Potential > OCV (e.g., 1.39V, 1.5V): You are applying an anodic (charging) potential. This drives the Oxygen Evolution Reaction (OER) on the air electrode and zinc deposition on the zinc electrode. These are highly efficient Faradaic processes. Potential < OCV (e.g., 1.37V): You are applying a cathodic (discharging) potential. This drives the Oxygen Reduction Reaction (ORR) on the air electrode and zinc dissolution on the zinc electrode.
• The “Non-Faradaic” region for a battery is infinitesimally small right around the OCV. In a real, functioning battery, the kinetics are often so fast that even a tiny deviation of a few millivolts from OCV can produce a significant current. What you are attempting is not measuring a capacitive region, but rather initiating the full charge/discharge reaction of the battery.

2. Short Circuit in the Cell

This is a very common issue in coin cells or custom-built cells.

• Cause: The separator might have a tear, a puncture, or might be too thin. A zinc dendrite from a previous experiment could have pierced the separator. A gasket might be misaligned, allowing the zinc anode to touch the air cathode case.
• Symptom: The OCV might be lower than expected or decay rapidly. When you apply any potential, you are essentially passing current through a low-resistance short, leading to a massive current flow and immediate instrument overload.

3. Incorrect Two-Electrode Setup or Connections

• Working/Sense Leads: In a two-electrode setup, the Working Electrode (WE) and Working Sense (S1) leads are typically shorted together and connected to one electrode (e.g., the Air Cathode).
• Counter/Reference Leads: The Counter Electrode (CE) and Reference Electrode (RE) leads are shorted together and connected to the other electrode (e.g., the Zinc Anode).
• Mistake: If the connections are swapped (e.g., you connect the Zinc anode to the WE leads), the potentiostat will try to control the potential in the wrong direction, which can lead to instability and overload. Ensure the Zinc Anode (which is oxidized during discharge) is connected to the CE/RE leads (negative terminal) and the Air Cathode is connected to the WE/S1 leads (positive terminal).

Systematic Troubleshooting Plan

Follow these steps methodically to diagnose and solve the problem.

Step 1: Verify the Cell Integrity

Step 2: Re-evaluate Your Experimental Goal and Parameters

This is the most critical step. You cannot measure a wide non-Faradaic window on a full battery cell. You need to change your experiment.

• If your goal is to study capacitance: You are using the wrong system. Capacitance measurements are typically done on a single electrode (e.g., the air cathode) in a three-electrode setup against a stable reference electrode (like Ag/AgCl or Hg/HgO) in a potential region where that specific electrode is electrochemically inert. You cannot do this in a two-electrode full battery configuration.
• If your goal is to study the charge/discharge behavior (ORR/OER): This is what your experiment is actually doing. In this case, your potential window and scan rate are the problem.Drastically Reduce the Potential Window: Instead of 1.4V to 1.5V (a 100 mV window), try a much smaller window around the OCV. Start with ±10 mV: Set your window from 1.37V to 1.39V (assuming OCV is 1.38V). If that works, expand slowly: Try 1.36V to 1.40V. Drastically Reduce the Scan Rate: A fast scan rate demands a fast change in current. Your system can’t keep up. Start very slow: 1 mV/s or even 0.5 mV/s. This gives the system more time to respond without drawing a massive instantaneous current. Set Manual Current Limits: In your potentiostat software (e.g., EC-Lab, Nova, Aftermath), you can almost always set safety or range limits. Set a maximum current: Set the “Max Current” or “Current Range” to a reasonable value for your cell, for example, 10 mA or 50 mA. This will force the potentiostat to stop before it overloads its own hardware, giving you a more controlled result (the CV will look “clipped” at the top).

Step 3: A Recommended Experiment to Start

Here is a concrete set of parameters to try for a Linear Sweep Voltammetry (LSV) or a single Cyclic Voltammetry (CV) cycle on your two-electrode Zinc-Air cell:

Run this experiment. You should get a very narrow, tilted ellipse-like shape. The current going up from OCV is the charging current (OER), and the current going down from OCV is the discharging current (ORR). This is your battery’s polarization curve near equilibrium. From here, you can slowly expand the potential window and increase the scan rate to probe the kinetics further.

By taking these steps, you will move from a state of instrument overload to collecting meaningful data about your battery’s electrochemical behavior.