scholarly journals Understanding Potential-dependent Competition Between Electrocatalytic Dinitrogen and Proton Reduction Reactions

2021 ◽  
Author(s):  
Changhyeok Choi ◽  
Geun Ho Gu ◽  
Juhwan Noh ◽  
Hyun S. Park ◽  
Yousung Jung
Keyword(s):  
Charge Transfer ◽  
Heterogeneous Catalysts ◽  
Early Stage ◽  
Side Reaction ◽  
Potential Method ◽  
Reaction Rates ◽  
Reduction Reaction ◽  
Metal Catalyst ◽  
Proton Reduction ◽  
Catalyst Surfaces

Abstract One of the key challenges to practical electrochemical N2 reduction reaction (NRR) is to lower the overpotential and suppression of the side reaction known as the hydrogen evolution reaction (HER) during the NRR. The experimental NRR activity has been consistently shown to reach a maximum at early stage before reaching the mass-transfer limit and decreases with large overpotentials for many heterogeneous catalysts. Though the volcano-type current-potential relationship shown for NRR is unusual with limited reaction rates at higher overpotentials, the mechanistic origin has not been clearly explained, making the design principles for practical NRR still lacking. Herein, we investigate the potential-dependent reaction activity of NRR and HER using the constant electrode potential method and microkinetic modeling. It manifests the dominating proton adsorption over dinitrogen at small overpotentials leading to the inadequate reaction selectivity towards NRR at many metal catalyst surfaces. A clear potential-dependent competition between the N2 adsorption and *H formation is characterized by the degree of charge transfer in the adsorption process. It is also demonstrated that the larger charge transfer in *H formation is a general phenomenon applied to all heterogeneous catalyst surfaces considered here, that poses a fundamental challenge to realize practical electrochemical NRR. We suggest several strategies to overcome the latter challenges based on the present understandings.

scholarly journals Understanding potential-dependent competition between electrocatalytic dinitrogen and proton reduction reactions

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Changhyeok Choi ◽  
Geun Ho Gu ◽  
Juhwan Noh ◽  
Hyun S. Park ◽  
Yousung Jung
Keyword(s):  
Mass Transfer ◽  
Charge Transfer ◽  
Hydrogen Evolution Reaction ◽  
Electrode Potential ◽  
Heterogeneous Catalysts ◽  
Potential Model ◽  
Reduction Reaction ◽  
General Phenomenon ◽  
Proton Reduction ◽  
Fundamental Challenge

AbstractA key challenge to realizing practical electrochemical N2 reduction reaction (NRR) is the decrease in the NRR activity before reaching the mass-transfer limit as overpotential increases. While the hydrogen evolution reaction (HER) has been suggested to be responsible for this phenomenon, the mechanistic origin has not been clearly explained. Herein, we investigate the potential-dependent competition between NRR and HER using the constant electrode potential model and microkinetic modeling. We find that the H coverage and N2 coverage crossover leads to the premature decrease of NRR activity. The coverage crossover originates from the larger charge transfer in H+ adsorption than N2 adsorption. The larger charge transfer in H+ adsorption, which potentially leads to the coverage crossover, is a general phenomenon seen in various heterogeneous catalysts, posing a fundamental challenge to realize practical electrochemical NRR. We suggest several strategies to overcome the challenge based on the present understandings.

Microporous cobaloxime–graphene composite: a reloadable non-noble metal catalyst platform for the proton reduction reaction

2017 ◽  
Vol 5 (5) ◽  
pp. 1957-1961 ◽  
Author(s):  
Ahmed B. Soliman ◽  
Rana R. Haikal ◽  
Arwa A. Abugable ◽  
Mohamed H. Alkordi
Keyword(s):  
Heterogeneous Catalyst ◽  
Noble Metal ◽  
Reduction Reaction ◽  
Metal Catalyst ◽  
Graphene Sheets ◽  
Noble Metal Catalyst ◽  
Proton Reduction ◽  
One Pot ◽  
Graphene Composite

A heterogeneous catalyst for the proton reduction reaction was constructed through immobilization of cobaloxime, in a microporous solid, atop unmodified graphene sheets through a one-pot reaction.

Electrolyte Based Modeling of Corrosion Processes in Sulfuric Acid Mixtures – Part 1: Non-Oxidizing Conditions

CORROSION ◽  
10.5006/3872 ◽  
2021 ◽  
Author(s):  
Narasi Sridhar ◽  
Andrzej Anderko
Keyword(s):  
Sulfuric Acid ◽  
Corrosion Rate ◽  
Weight Percent ◽  
Reaction Rates ◽  
Reduction Reaction ◽  
Proton Reduction ◽  
Mole Percent ◽  
Active Dissolution ◽  
Experimental Values ◽  
Electrochemical Model

The corrosion behavior of stainless steels and Ni-base alloys in non-oxidizing sulfuric acid mixtures at concentrations below approximately 30 moles/Kg H2O is modeled. The redox potential in sulfuric acid across a broad concentration range, from 0 to 80 mole percent (0 to 95.6 weight percent), is determined by the proton reduction reaction. Thus, in the absence of other oxidizing species, sulfuric acid behaves as a non-oxidizing (reducing) acid. The calculated corrosion rate, using an electrochemical model up to about 30 moles/Kg H2O (about 75 weight percent) is in agreement with experimental values. The predicted polarization curves of anodic and cathodic processes showed that the alloys in these environments are in active dissolution regime, consistent with experimental data. The model predictions of corrosion rates in H2SO4+HCl, H2SO4+HF, and H2SO4+HCl+HF mixtures are in agreement with weight-loss corrosion data. The corrosion rate of alloys in the non-oxidizing sulfuric acid mixtures correlated to an equivalent alloy composition given by (Ni0.7-Cr0.1+Mo+0.5W). The effect of alloying elements under these conditions may be related to their beneficial effect on active dissolution and proton reduction reaction rates.

What catalysis needs from the electron microscopist

1988 ◽  
Vol 46 ◽  
pp. 694-695
Author(s):  
Alexis T. Bell
Keyword(s):  
Active Sites ◽  
Heterogeneous Catalysts ◽  
Catalyst Deactivation ◽  
Surface Composition ◽  
Internal Surface ◽  
Active Phase ◽  
Atomic Scale ◽  
Metal Catalyst ◽  
Internal Surface Area ◽  
Porous Support

Heterogeneous catalysts, used in industry for the production of fuels and chemicals, are microporous solids characterized by a high internal surface area. The catalyticly active sites may occur at the surface of the bulk solid or of small crystallites deposited on a porous support. An example of the former case would be a zeolite, and of the latter, a supported metal catalyst. Since the activity and selectivity of a catalyst are known to be a function of surface composition and structure, it is highly desirable to characterize catalyst surfaces with atomic scale resolution. Where the active phase is dispersed on a support, it is also important to know the dispersion of the deposited phase, as well as its structural and compositional uniformity, the latter characteristics being particularly important in the case of multicomponent catalysts. Knowledge of the pore size and shape is also important, since these can influence the transport of reactants and products through a catalyst and the dynamics of catalyst deactivation.

Promoting interfacial charge transfer by B/N co-doping enable efficient ORR catalysis of carbon encapsulated Fe2N

2022 ◽  
Author(s):  
Zhi Xie ◽  
Qiaoling Li ◽  
Xingkai Peng ◽  
Xuewei Wang ◽  
Lingli Guo ◽  
...  
Keyword(s):  
Charge Transfer ◽  
Oxygen Reduction Reaction ◽  
Oxygen Reduction ◽  
Porous Carbon ◽  
High Efficiency ◽  
Reduction Reaction ◽  
Carbon Shell ◽  
Co Doping ◽  
Interfacial Charge ◽  
Electrochemical Catalysts

High efficiency and durability are two key targets for developing electrochemical catalysts for oxygen reduction reaction (ORR). Here, B/N co-doping porous carbon shell encapsulated Fe2N nanoparticles (NPs) was synthesized as...

On the Kinetics and Mechanism of Spontaneous Intramolecular Reduction of the Central Metal Ion in K2[Mn(IV)-2-α-hydroxyethyl isochlorin e4] Acetate in Aqueous Alkaline Solutions and its Relation to the Binding Sites of Manganese in Photosynthesis

1975 ◽  
Vol 30 (5-6) ◽  
pp. 327-332 ◽  
Author(s):  
Gerhard Vierke ◽  
Manfred Müller
Keyword(s):  
Electron Transfer ◽  
Metal Ion ◽  
Reaction Rates ◽  
Bimolecular Reaction ◽  
Reduction Reaction ◽  
Alkaline Solutions ◽  
Central Metal ◽  
Pseudo First Order Reaction ◽  
Spontaneous Reduction ◽  
Acid Base Equilibrium

Abstract Spectrophotometric investigation of the kinetics of the spontaneous reduction of the central metal ion in K2[Mn (IV)-2-α-hydroxyethyl-isochlorine e4] acetate in aqueous alkaline solution in the absence of any reducing agent reveals that it is a pseudo-first order reaction which is specifically hydroxide ion catalyzed. The pKα-value of the acid-base equilibrium has been estimated to be 14.4. Electron transfer to the central metal ion is the rate limiting step. The measurements of its temperature dependence yields an activation enthalpy of ∆H‡ = 12 kcal/mol and an entropy of activation ∆S‡ = - 30 e.u. thus indicating that the electron transfer step is a bimolecular reaction. The most likely reactant is water. The reduction reaction does not take place with appreciable reaction rates at physiological pH. Thus, when bound to a suitable ligand of the chlorin type, Mn (IV)-compounds are sufficiently stable with respect to autoxidation to play some role in biological redox reactions as postulated recently for the photoreactivation process of the water splitting system in photosynthesis.

Sign in / Sign up

Export Citation Format

Share Document