Tuning the Electronic Structure of a Ni-Vacancy-Enriched AuNi Spherical Nanoalloy via Electrochemical Etching for Water Oxidation Studies in Alkaline and Neutral Media

Abstract

Internal Ni-vacancy-enriched spherical AuNi nanoalloys (AuNi1–2-T) have been prepared via a noble electrochemical etching method. AuNi1.5-T showed the highest oxygen evolution reaction (OER) activity compared to bare AuNi1.5, and it demands only 239 mV overpotential, which was 134 mV lesser than the overpotential required by commercial RuO2 at 10 mA cm–2 current density in a 1 M KOH solution (pH = 14). The calculated turnover frequency (TOF) value for AuNi1.5-T (0.0229 s–1) was 11.74 times higher than that of AuNi1.5 (0.00195 s–1). Also, the electrochemically activated AuNi1.5-T showed superior neutral water oxidation activity by demanding only 335 mV overpotential with a TOF value of 0.000135 s–1 in a 1 M Na2SO4 solution (pH = 7) at 10 mA cm–2. The long-term stability studies (over 60 h) reveal the excellent robustness of an electrochemically treated alloy system. Density functional theory based electronic structure calculations showed that in the case of AuNi and AuNi1.5, Au d, Au s, and Ni d orbitals have significant contributions, whereas in the Ni-vacant systems, the density of states is mainly governed by d orbitals of Au and Ni. Also, the Ni-vacant system possesses a work function value of 4.96 eV, which is lower than that of the pristine system (5.27 eV) and thereby favored OH– binding with an optimum adsorption energy. This result is in reasonable agreement with the experimental outcome of an accelerated OER in a vacancy-enriched Ni-rich AuNi alloy system. Also, mechanistic analysis reveals that the creation of a Ni vacancy can effectively alter the overall mechanism of the OER and thereby facilitate the same with a lower applied energy.

Atmospheric-Water-Induced Reversible Structural Transformation of a Two-Dimensional Ni(II)-Based Ferromagnetic MOF: A Highly Efficient Water Oxidation Electrocatalyst and Colorimetric Water Sensor

“…The observed potential data were obtained by using the Ag/AgCl reference electrode, and the corresponding data were changed to the reference of a reversal hydrogen electrode ( E RHE ) by using the Nernst equation E RHE = E Ag/AgCl + 0.0591 × pH + 0.197. The overpotential (η) calculation is based on the equation η = E RHE – 1.23 V . The Tafel slope was estimated from the fitting of the overpotential versus log j following the Tafel equation η = b log­( j / j 0 ), where b corresponds to the expected slope, j 0 designates the exchange current density, and j is the current density .…”

Exploring the linear relationship between potential dynamics and interfacial capacitance: implications for enhancing the turnover frequency in electrochemical water splitting

“…Eqn (1) is the most common one used to calculate the TOF value of an electrocatalystwhere J is the current density at a defined overpotential value; N A is Avogadro's number; F is Faraday's constant (96 485 C mol −1 ); n is the number of electron transfer; and τ is the electrochemically active sites (ECAS). 11–15…”

Ultrafine IrRu Nanoparticles toward Efficient Oxygen Evolution Reaction in Acidic Media

“…Water electrolysis has been regarded as one of the most promising strategies for widespread hydrogen production. PEMWEs and alkaline water electrolyzers (AWEs) represent two major hydrogen production technologies. − PEMWEs can produce much purer hydrogen at a larger current density and a higher energy efficiency as compared to AWEs. However, a grand challenge of PEMWEs is the slow kinetics of acidic OER, which involves multiple electron transfer and a high reaction energy barrier .…”