Uncovering the Change in Catalytic Activity during Electro-oxidation of Urea: Answering Overisolation of the Relaxation Phenomenon

Bibhudatta Malik, Kalimuthu Vijaya Sankar, S. K.Tarik Aziz, Sumit Majumder, Yoed Tsur, Gilbert D. Nessim

Research output: Contribution to journalArticlepeer-review

8 Scopus citations

Abstract

Electro-oxidation of urea offers tremendous opportunity for the economical hydrogen production option owing to its lower thermodynamic potential barriers. Slower reaction rate and multiple gas desorption steps hinder the implementation of urea-based fuel cells, and thus understanding the urea oxidation process is key for the commercialization of this technology. In this report, we systematically examined the electrocatalytic urea oxidation activity of nickel-based model catalysts such as Ni12P5and Ni(OH)2in an alkaline medium at a fixed urea concentration of 0.33 M using electrochemical impedance spectroscopy (EIS). Ni12P5and Ni(OH)2require potentials of 0.51 and 0.54 V vs Hg/HgO, respectively, to achieve a current density of 10 mA cm-2. The origin of the catalytic activity difference of the urea oxidation reaction (UOR) between these two Ni catalysts is briefly analyzed using nondestructive in situ EIS. We measured the electrochemical impedance spectra of both the catalysts at their faradic potentials, and the obtained Nyquist plots suggest that the depressed arcs possess more than one time constant. We used the impedance spectroscopy genetic programing (ISGP) method to obtain the distribution function of relaxation times (DFRTs). DFRTs show the existence of three relaxation processes that occur during the anodic UOR, which are the effect of pores or active material (P1), charge transfer resistance related to oxidation of Ni (P2), and charge transfer resistance associated with oxidation of urea (P3). The location of P2 and P3 at higher frequencies for Ni12P5compared to its counterpart Ni(OH)2confirms that Ni12P5can be a better catalyst.

Original languageEnglish
Pages (from-to)23126-23132
Number of pages7
JournalJournal of Physical Chemistry C
Volume125
Issue number42
DOIs
StatePublished - 28 Oct 2021

Bibliographical note

Publisher Copyright:
© 2021 American Chemical Society

Funding

The authors acknowledge the support of the Planning and Budgeting Committee, Israel Council for Higher Education, and the Fuel Choice Initiative within the framework of the Israel National Research Center for Electrochemical Propulsion (INREP) for funding this study.

FundersFunder number
Fuel Choice Initiative
Council for Higher Education
Israel National Research Center for Electrochemical Propulsion

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