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The catalytic performance of Mo3P nanoparticles is tested in the hydrogen evolution reaction (HER), indicating an onset potential of as low as 21 mV, H2 formation rate, and exchange current density of 214.7 μmol/(s·g) cat (at only 100 mV overpotential) and 279.07 μA/cm 2, respectively, which are among the closest values yet observed to platinum.
In acidic conditions, the hydrogen evolution reaction follows the formula: [6] 2 H + + 2 e − → H 2. In neutral or alkaline conditions, the reaction follows the formula: [6] 4 H 2 O + 4 e − → 2 H 2 + 4 HO −. Both of these mechanisms can be seen in industrial practices at the cathode side of the electrolyzer where hydrogen evolution occurs.
For example, hydrogen is oxidized and protons are reduced readily at the platinum surface of a standard hydrogen electrode in aqueous solution, in a Hydrogen Evolution Reaction. Substituting an electrocatalytically inert glassy carbon electrode for the platinum electrode produces irreversible reduction and oxidation peaks with large overpotentials.
The data below tabulates standard electrode potentials (E°), in volts relative to the standard hydrogen electrode (SHE), at: Temperature 298.15 K (25.00 °C; 77.00 °F); Effective concentration (activity) 1 mol/L for each aqueous or amalgamated (mercury-alloyed) species; Unit activity for each solvent and pure solid or liquid species; and
The net cell reaction yields hydrogen and oxygen gases. The reactions for one mole of water are shown below, with oxidation of oxide ions occurring at the anode and reduction of water occurring at the cathode. Anode: 2 O 2− → O 2 + 4 e −. Cathode: H 2 O + 2 e − → H 2 + O 2−. Net Reaction: 2 H 2 O → 2 H 2 + O 2
However, the total cell potential (difference between oxidation and reduction half cell potentials) will remain 1.23 V. This potential can be related to Gibbs free energy (ΔG) by: ΔG°cell = −nFE°cell Where n is the number of electrons per mole products and F is the Faraday constant. Therefore, it takes 475 kJ of energy to make one mole of ...
The values below are standard apparent reduction potentials (E°') for electro-biochemical half-reactions measured at 25 °C, 1 atmosphere and a pH of 7 in aqueous solution. [1] [2] The actual physiological potential depends on the ratio of the reduced (Red) and oxidized (Ox) forms according to the Nernst equation and the thermal voltage.
In electrochemistry, the Nernst equation is a chemical thermodynamical relationship that permits the calculation of the reduction potential of a reaction (half-cell or full cell reaction) from the standard electrode potential, absolute temperature, the number of electrons involved in the redox reaction, and activities (often approximated by concentrations) of the chemical species undergoing ...