Linear sweep
One-way sweep to a diffusion-limited plateau.
One sweep, one direction: the current rises through a wave to a diffusion-limited plateau. From that single curve come the onset potential, the Tafel slope, and the exchange current density, the working vocabulary of electrocatalysis and stability screening.
What it measures
LSV sweeps potential in one direction at a fixed rate and records the current response. Each region of the resulting wave carries a different parameter:
- Onset potential: where faradaic current departs from baseline, defined honestly only against a stated current-density criterion.
- Tafel region: η = a + b·log i. The slope b reads the mechanism: ~60 mV/decade and ~120 mV/decade point at different rate-determining steps. The intercept yields the exchange current density i₀, the intrinsic activity, with the transfer coefficient α from the same fit.
- Limiting plateau: current capped by how fast species reach the electrode. On a rotating disk electrode the Levich equation, i_lim = 0.620 · n F A D²ᐟ³ ω¹ᐟ² ν⁻¹ᐟ⁶ C, ties the plateau to rotation rate ω; the Koutecky-Levich form, 1/i = 1/i_k + 1/i_lim, separates kinetic from transport current.
How to read the output
Read the curve in order. The foot tells you when chemistry starts: for a catalyst that is activity; for an electrolyte it is the breakdown limit. The Tafel slope tells you how the reaction gets faster with overpotential, and is only meaningful fit over a clean decade of current, below the onset of transport limitation. The plateau tells you about supply, not kinetics: if it scales with √ω on an RDE, it is genuine mass transport. For catalyst comparisons, the overpotential at a benchmark current density , 10 mA/cm² for OER and HER, is the single number that travels between labs, and it is only comparable when iR compensation is applied and stated.
A real use case
An electrolyte team is screening additive packages for a high-voltage NMC cell that must charge to 4.4 V. LSV on each formulation, swept anodically on an inert electrode, puts the oxidation onset on one axis: the baseline formulation shows oxidation current rising from ~4.3 V, inside the operating window, while two of five additive packages push onset past 4.55 V. Defined against a fixed current criterion rather than read by eye, those onsets rank the formulations defensibly, and only the two survivors advance to full cell builds. One sweep per formulation, minutes each, replaces weeks of cycling to discover the same ranking.
Common mistakes
- Skipping iR compensation. Uncompensated solution resistance inflates every potential reading and makes Tafel slopes and benchmark overpotentials incomparable.
- Reading onset “by eye.” Without a stated current-density criterion, onset is whatever the reader wants it to be.
- Fitting a Tafel slope over less than a decade of current, or into the transport-limited region, both produce slopes that look plausible and mean nothing.
- Sweeping too fast. Capacitive background scales with scan rate and buries the faradaic foot of the wave.
- Comparing catalysts at different loadings or without normalizing to the same area basis, geometric versus ECSA changes the ranking.
From raw sweep to ranked readout
Niobia ingests LSV data from BioLogic, PalmSense, Gamry, and generic instrument exports, plots the polarization curve, and extracts the working numbers: onset potential against an explicit criterion, Tafel slope and exchange current density from a validated fitting region, and the transfer coefficient. For rotating disk data it runs the Levich and Koutecky-Levich constructions to separate kinetics from transport, and it computes overpotential at benchmark current densities, 10 mA/cm² for OER/HER, with iR-compensation guidance so the numbers compare across experiments. Multi-sample sweeps come back as an overlay with the extracted parameters tabulated, which is what turns a screening study into a ranking.
Frequently asked
When is LSV the right choice over cyclic voltammetry?
When the question is one-directional: onset of a reaction, catalyst polarization, electrolyte breakdown. CV’s return sweep adds reversibility information; LSV trades it for a cleaner read of a single wave.
What does the Tafel slope actually tell you?
The mechanism’s rate-determining step. Slopes near 60 mV/decade versus 120 mV/decade implicate different limiting steps, and a slope that drifts with potential usually means the fit window strayed out of kinetic control.
Why does everyone quote overpotential at 10 mA/cm²?
It is the community benchmark for solar-fuel-relevant current densities in OER/HER work, a fixed operating point that makes catalysts comparable across labs, provided iR compensation and area normalization are stated.