In 1833, English experimental physicist Michael Faraday (1791–1867) presented his landmark paper “Experimental Researches in Electricity. Seventh Series” to the Royal Society of London, establishing the quantitative Laws of Electrolysis.

Faraday proved that the amount of chemical decomposition produced by an electric current is strictly proportional to the total electric charge passing through an electrolyte solution.

In collaboration with Cambridge polymath William Whewell, Faraday coined the universal terminology of modern electrochemistry—introducing the terms Electrolysis, Electrolyte, Electrode, Anode, Cathode, Ion, Cation, and Anion. Faraday’s laws yielded the Faraday Constant ($F = N_{\text{A}} e$), provided the first quantitative evidence for the quantization of electric charge, and underpins modern lithium-ion batteries and green hydrogen production.

Faraday’s Two Laws of Electrolysis

Through painstaking quantitative measurements using a self-designed gas-measuring Voltameter (Coulometer), Faraday established two fundamental laws governing electrochemical reactions:

1. Faraday’s First Law of Electrolysis

The mass ($m$) of a chemical substance liberated, deposited, or dissolved at an electrode during electrolysis is directly proportional to the total electric charge ($Q$) passed through the electrolyte:

$$m \propto Q \implies m = Z Q = Z I t$$

Where:

  • $Q = I t$ is total electrical charge in Coulombs ($\text{C}$), given electric current $I$ (Amperes) and duration $t$ (seconds).
  • $Z$ is the electrochemical equivalent of the substance ($\text{kg/C}$ or $\text{g/C}$).

2. Faraday’s Second Law of Electrolysis

When the same quantity of electric charge ($Q$) is passed through different electrolyte solutions, the masses ($m_1, m_2$) of different elements liberated at the electrodes are directly proportional to their respective chemical equivalent weights ($E = M / z$):

$$m \propto \frac{M}{z} \implies \frac{m_1}{m_2} = \frac{M_1 / z_1}{M_2 / z_2}$$

Where:

  • $M$ is the molar mass of the element ($\text{g/mol}$).
  • $z$ is the valence number (ionic charge number of the ion in solution).

The Universal Electrolysis Equation & Faraday Constant

Combining Faraday’s First and Second Laws into a single universal equation:

$$m = \left( \frac{M}{z F} \right) Q = \frac{M I t}{z F}$$

Where $F$ is the Faraday Constant—the total electric charge carried by one mole of single-charged valence electrons:

$$F = N_{\text{A}} e \approx 96,485.33219 \quad \text{Coulombs / mole}$$

Where: * $N_{\text{A}} \approx 6.02214 \times 10^{23}\,\text{mol}^{-1}$ is Avogadro’s constant. * $e \approx 1.6021766 \times 10^{-19}\,\text{Coulombs}$ is the elementary unit of electric charge.

The Quantization of Electricity: Prefiguring the Electron

Faraday’s Laws of Electrolysis provided the first compelling experimental proof that electricity is atomic and discrete in nature, rather than a continuous fluid.

In his 1881 Faraday Memorial Lecture, German physicist Hermann von Helmholtz pointed out the inescapable physical implication of Faraday’s 1833 work:

“If we accept the hypothesis that the elementary substances are composed of atoms, we cannot avoid concluding that electricity also, both positive and negative, is divided into definite elementary quanta, which behave like atoms of electricity.”

Ten years later, in 1891, Irish physicist George Johnstone Stoney coined the term “electron” to denote this fundamental unit of electric charge derived directly from Faraday’s electrochemical ratio $e = F / N_{\text{A}}$.

Coining the Vocabulary of Electrochemistry

To explain his experimental findings, Faraday consulted scholar William Whewell in 1834 to construct a precise Greek-derived scientific nomenclature:

  • Electrolysis: Chemical breakdown produced by electricity (electro + lysis = loosening by electricity).
  • Electrolyte: A liquid medium containing free mobile ions that conducts electric current.
  • Electrode: The conductor through which current enters or leaves an electrolyte.
  • Anode: The positive electrode where oxidation occurs (anodos = way up).
  • Cathode: The negative electrode where reduction occurs (kathodos = way down).
  • Ion: A charged atom or molecule carrying electric current through liquid (ion = wanderer).
  • Cation: A positively charged ion migrating toward the negative cathode ($\text{e.g., Na}^+, \text{Cu}^{2+}$).
  • Anion: A negatively charged ion migrating toward the positive anode ($\text{e.g., Cl}^-, \text{SO}_4^{2-}$).

Bridge to Quantum Electrochemistry & Green Energy Technologies

In modern physics and energy engineering, Faraday’s 1833 laws govern advanced electrochemical energy storage:

1. Lithium-Ion Battery Storage & Energy Density

In modern lithium-ion batteries powering electric vehicles and smartphones, $\text{Li}^+$ ions undergo reversible electrochemical intercalation into cathode ($\text{LiCoO}_2$) and anode ($\text{C}_6$) host lattices.

The theoretical specific charge capacity $C_{\text{theoretical}}$ ($\text{mAh/g}$) of any battery material is calculated directly from Faraday’s law:

$$C_{\text{theoretical}} = \frac{z F}{3.6 \times M_{\text{active}}}$$

Where $M_{\text{active}}$ is the molar mass of the active electrode material.

2. Green Hydrogen Electrocatalysis & Quantum DFT

The production of zero-carbon green hydrogen fuel by water splitting ($2\text{H}_2\text{O} \rightarrow 2\text{H}_2 + \text{O}_2$) obeys Faraday’s law of charge conservation.

Modern Quantum Electrochemistry uses Density Functional Theory (DFT) to calculate the Overpotential ($\eta$) and Gibbs free energy of adsorption ($\Delta G_{\text{H}^*}$) on catalyst surfaces (Pt, $\text{IrO}_2$), optimizing quantum electron transfer rates across the electrochemical double layer (Marcus-Hush theory).

Key Takeaways

  • Year: 1833
  • Key Figure: Michael Faraday (English Experimentalist & Physicist)
  • Core Discovery: Established Faraday’s Laws of Electrolysis ($m = \frac{M I t}{z F}$), linking electrical charge directly to chemical mass.
  • Fundamental Constant: Defined the Faraday constant $F = N_{\text{A}} e \approx 96,485\,\text{C/mol}$.
  • Vocabulary Invention: Coined the terms electrolyte, electrode, anode, cathode, ion, cation, anion with William Whewell.
  • Atomic Precursor: Provided the quantitative proof for discrete electric charge, leading Stoney to name the electron.
  • Modern Relevance: Underpins lithium-ion battery capacity design, fuel cells, and quantum electrocatalysis for green hydrogen production.