Potentiostat

Key takeaways

Potentiostat belongs to chemistry; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Potentiostat to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Potentiostat from memory before moving on to harder problems.

Reference excerpt

A potentiostat is the electronic hardware required to control a three electrode cell and run most electroanalytical experiments. A Bipotentiostat and polypotentiostat are potentiostats capable of controlling two working electrodes and more than two working electrodes, respectively. The system functions by maintaining the potential of the working electrode at a constant level with respect to the reference electrode by adjusting the current at an auxiliary electrode. The heart of the different potentiostatic electronic circuits is an operational amplifier (op amp). It consists of an electric circuit which is usually described in terms of simple op amps.

Primary use This equipment is fundamental to modern electrochemical studies using three electrode systems for investigations of reaction mechanisms related to redox chemistry and other chemical phenomena. The dimensions of the resulting data depend on the experiment. In voltammetry, electric current in amps is plotted against electric potential in voltage. In a bulk electrolysis total coulombs passed (total electric charge) is plotted against time in seconds even though the experiment measures electric current (amperes) over time. This is done to show that the experiment is approaching an expected number of coulombs. Most early potentiostats could function independently, providing data output through a physical data trace. Modern potentiostats are designed to interface with a personal computer and operate through a dedicated software package. The automated software allows the user rapidly to shift between experiments and experimental conditions. The computer allows data to be stored and analyzed more effectively, rapidly, and accurately than the earlier standalone devices.

Basic relationships A potentiostat is a control and measuring device. It comprises an electric circuit which controls the potential across the cell by sensing changes in its resistance, varying accordingly the current supplied to the system: a higher resistance will result in a decreased current, while a lower resistance will result in an increased current, in order to keep the voltage constant as described by Ohm's law.

R = E I {\displaystyle {R}={E \over I}}

As a result, the variable system resistance and the controlled current are inversely proportional

I o = E c R v {\displaystyle I_{o}={E_{c} \over R_{v}}}

I o {\displaystyle I_{o}} is the output electric current of the potentiostat

E c {\displaystyle E_{c}} is the voltage that is kept constant

R v {\displaystyle R_{v}} is the electrical resistance that varies.

Principles of operation Since 1942, when the English electrochemist Archie Hickling (University of Leicester) built the first three electrode potentiostat, substantial progress has been made to improve the instrument. Hickling's device used a third electrode, the reference electrode to control the cell potential automatically. Up until the present day his principle has remained in use. At a glance, a potentiostat measures the potential difference between the working and the reference electrode, applies the current through the counter electrode and measures the current as an i {\displaystyle i} R {\displaystyle R} voltage drop over a series resistor ( R m {\displaystyle R_{\textrm {m}}} in Fig. 1). The control amplifier (CA) is responsible for maintaining the voltage between the reference and the working electrode as closely as possible to the voltage of the input source E i {\displaystyle E_{\textrm {i}}} . It adjusts its output to automatically control the cell current so that a condition of equilibrium is satisfied. The theory of operation is best understood using the equations below. Prior to observing the following equations, one may note that, from an electrical point of view, the electrochemical cell and the current measurement resistor R m {\displaystyle R_{\textrm {m}}} may be regarded as two impedances (Fig. 2). Z 1 {\displaystyle Z_{1}} includes R m {\displaystyle R_{\textrm {m}}} in series with the interfacial impedance of the counter electrode and the solution resistance between the counter and the reference. Z 2 {\displaystyle Z_{2}}

represents the interfacial impedance of the working electrode in series with the solution resistance between the working and the reference electrodes.

The role of the control amplifier is to amplify the potential difference between the positive (or noninverting) input and the negative (or inverting) input. This may be translated mathematically into the following equation:

… excerpt ends here. Continue reading the full article.

Illustrations

Potentiostat: Fig. 1 : Schematic of a potentiostat. — Fig. 1 : Schematic of a potentiostat.

Potentiostat: Fig. 2 : Schematic of a potentiostat, with electrochemical cell replaced by two impedances. — Fig. 2 : Schematic of a potentiostat, with electrochemical cell replaced by two impedances.

Worked examples

Example 1 — a first encounter with Potentiostat

Start with the simplest possible case. Write down what Potentiostat claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In chemistry, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Potentiostat before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Potentiostat ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Potentiostat

In research: Potentiostat appears in chemistry research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Potentiostat in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Potentiostat is common in secondary-school and first-year university syllabi. It links to neighbouring topics Electroanalytical chemistry devices, Electronic engineering, so understanding it makes those chapters shorter.
In everyday life: Look for Potentiostat outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

How to study Potentiostat in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Potentiostat means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Potentiostat out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Potentiostat in simple terms?

A potentiostat is the electronic hardware required to control a three electrode cell and run most electroanalytical experiments. A Bipotentiostat and polypotentiostat are potentiostats capable of controlling two working electrodes and more than two working electrodes, respectively.

Why does Potentiostat matter?

Because it connects several chemistry ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Potentiostat?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Potentiostat.