Hydrogen Production Science and Technology

Thermodynamic and Economic Potential of Glycerol Oxidation to Replace Oxygen Evolution in Water Electrolysis

“…Negative values mean that these reactions would run in a galvanic mode (i.e., spontaneous reaction converting the chemical energy into electricity) unless the overpotential losses lead to positive operating voltages in total (which is observed in experiments). We may also call this mode as a “fuel cell mode” according to the definition of a fuel cell [e.g., Lipman et al “Electrochemical device converting the chemical energy (Gibbs free energy) stored in a [···] fuel [···] into work of electrical energy (direct current electricity) at constant temperature”].…”

“…The “reversible voltage” E rev (also known as “equilibrium” or “theoretical” open-circuit voltage) is the minimal amount of electricity to reversibly drive the reaction, i.e., without any losses, at a given temperature (isothermal conditions) (see derivation in the Supporting Information). For calculating it at system temperature T , pressure p , and activity a i , the Nernst equation is commonly used E normalr normale normalv ( T , p , a i ) = E normalr normale normalv θ ( T , p ) − R T z F ∑ i = 1 n ν i ln ( a i ) It describes the difference between the standard reversible voltage with unit activities as a reference state E rev θ , with θ denoting an arbitrary reference condition, and the activities of the system species a i at operating concentrations …”

“…The specific reference states used in this study as well as what that means in terms of an actual electrolyzer are explained in section Regarding Reference States. Moreover, the reversible voltage is reaction-dependent and proportional to the molar-based Gibbs free energy of reaction Δ R G divided by the number of electrons transferred z E normalr normale normalv θ ( T , p ) = Δ R G θ ( T , p ) z F Depending on the available data, the Gibbs free energy of reaction, for any state thus dropping the superscript θ here, can be calculated either by summing over the individual species Gibbs free energies of formation Δ f G i (multiplied by the stoichiometric coefficients ν i ) or alternatively directly by the enthalpy of reaction Δ R H , the entropy of reaction Δ R S , and the reaction temperature T Δ R G ( T , p ) = ∑ i = 1 N ν i Δ f G i ( T , p ) = Δ R H ( T , p ) − T Δ R S ( T , p ) where Δ f G i ( T , p ) = Δ f H i ( …”

“…In fact, typically the overpotentials more than cover the difference between the reversible voltage and the thermoneutral voltage, and electrolyzers require cooling . The standard thermoneutral voltage can be calculated analogously to the standard reversible voltage E normalt normalh θ ( T , p ) = Δ R H θ ( T , p ) z F where the enthalpy of reaction is either directly available or calculated from the individual enthalpies of formation Δ R H θ ( T , p ) = ∑ i = 1 N ν i Δ f H i θ ( T , p ) Note that the standard thermoneutral voltage E th θ ( T 0 , p 0 ) is only applicable, i.e., only has physical meaning as representing isothermal and adiabatic operation, if the entropy of reaction Δ R S θ ( T 0 , p 0 ) is positive. Else, isothermal and adiabatic operation would imply entropy destruction by entropy balance, which is impossible by the second law of thermodynamics.…”

Nanomaterials: paving the way for the hydrogen energy frontier

“…While platinum nanoparticles have demonstrated efficacy in hydrogen fuel cells, their cost and limited availability impede large-scale applications. Consequently, researchers explore alternative nanomaterials, such as iron, nickel, and cobalt nanoparticles, as potential catalysts for hydrogen fuel cells [ 10 , 12 ]. Beyond storage and catalysis, nanomaterials are actively investigated for their role in hydrogen transport and delivery.…”