[MoS4]2--Intercalated NiCo-Layered Double Hydroxide Nanospikes: An Efficiently Synergized Material for Urine To Direct H2 Generation

Ayasha Nadeema; Varchaswal Kashyap; Rakshitha Gururaj; Sreekumar Kurungot

doi:10.1021/acsami.9b06545

[MoS₄]^2--Intercalated NiCo-Layered Double Hydroxide Nanospikes: An Efficiently Synergized Material for Urine To Direct H₂ Generation

ACS Appl Mater Interfaces. 2019 Jul 24;11(29):25917-25927. doi: 10.1021/acsami.9b06545. Epub 2019 Jul 11.

Authors

Ayasha Nadeema^{1

2}, Varchaswal Kashyap^{1

2}, Rakshitha Gururaj^{1

3}, Sreekumar Kurungot^{1

2}

Affiliations

¹ Physical and Materials Chemistry Division , CSIR-National Chemical Laboratory , Pune 411008 , India.
² Academy of Scientific and Innovative Research (AcSIR) , New Delhi 110001 , India.
³ Christ University , Bengaluru 560029 , India.

PMID: 31243949
DOI: 10.1021/acsami.9b06545

Abstract

Substituting the energy-uphill water oxidation half-cell with readily oxidizable urea-rich urine, a ground-breaking bridge is constructed, combining the energy-efficient hydrogen generation and environmental protection. Hence, designing a robust multifunctional electrocatalyst is desirable for widespread implementation of this waste to fuel technology. In this context, here, we report a simple tuning of the electrocatalytically favorable characteristics of NiCo-layered double hydroxide by introducing [MoS₄]^2- in its interlayer space. The [MoS₄]^2- insertion as well as its effect on the electronic structure tuning is thoroughly studied via X-ray photoelectron spectroscopy in combination with electrochemical analysis. This insertion induces overall electronic structure tuning of the hydroxide layer in such a way that the designed catalyst exhibited favorable kinetics toward all the required reactions of hydrogen generation. This is why our homemade catalyst, when utilized both as a cathode and anode to fabricate a urea electrolyzer, required a mere ∼1.37 V cell potential to generate sufficient H₂ by reaching the benchmark 10 mA cm^-2 in 1 M KOH/0.33 M urea along with long-lasting catalytic efficiency. Other indispensable reason of selecting [MoS₄]^2- is its high-valent nature making the catalyst highly selective and insensitive to common catalyst-poisoning toxins of urine. This is experimentally supported by performing the real urine electrolysis, where the nanospike-covered Ni foam-based catalyst showed a performance similar to that of synthetic urea, offering its industrial value. Other intuition of selecting [MoS₄]^2- was to provide a ligand-based mechanism for hydrogen evolution half-cell [hydrogen evolution reaction (HER)] to preclude the HER-competing oxygen reduction. Another crucial point of our work is its potential to avoid the mixing of two explosive product gases, that is, H₂ and O₂.

Keywords: hydrogen evolution reaction; layered double hydroxide; nickel oxyhydroxide; sewage denitrification; urea oxidation reaction; urine/urea electrolysis.