An Electrochemical Impedance Study of Alkaline Water Splitting Using Fe Doped NiO Nanosheets

Abstract

Mixed nickel-iron (Ni-Fe) compounds have recently emerged as promising non-precious electrocatalysts for alkaline water splitting. The understanding of the charge-transfer mechanism involved in the multi-step Faradic reaction, however, is still limited for the overall electrochemical process. In this paper, electrochemical impedance spectroscopy (EIS) measurements of Fe incorporated Ni oxide nanosheets were used to study the reaction kinetics for both hydrogen (HER) and oxygen (OER) evolution reactions in alkaline media. Our results showed that Fe incorporation improves the catalytic property of NiO nanosheets because of the lower reaction resistance and faster intermediate transformations. Detailed EIS modeling enables a separation of the surface coverage relaxation from the charge transfer resistance, with an inductive behavior observed in the low-frequency range for HER, holding important information on the dominating reaction mechanism. For OER, the good agreement between the EIS experimental results and a model with an inductance loop indicated that similar inductive behavior would be determining the EIS response at very low frequencies. The physical significance of the elementary steps gives insight into the governing reaction mechanisms involved in the electron and hole charge transfer, as well as the inherent properties of catalysts and their surface coverage relaxation.

Unveiling the Potential of Covalent Organic Framework Electrocatalyst for Enhanced Oxygen Evolution

“…The loop C PED -R D in the low-frequency region is associated with OER kinetics, where R D is the resistance associated with charge transfer during the adsorption−desorption process. 35 In comparison to the other COFs, the PT-30 COF has the lowest R D , which suggests faster OER kinetics (Figure 3f). The Tafel slope was used to assess the material's intrinsic catalytic activity.…”

“…In comparison to the Pristine-COF, the smaller semicircle of post-functionalized COFs exhibits greater electrocatalytic activity and a quicker rate of charge transfer for OER. The loop C PED -R D in the low-frequency region is associated with OER kinetics, where R D is the resistance associated with charge transfer during the adsorption–desorption process . In comparison to the other COFs, the PT-30 COF has the lowest R D , which suggests faster OER kinetics (Figure f).…”

Molecular-Scale Manipulation of Layer Sequence in Heteroassembled Nanosheet Films toward Oxygen Evolution Electrocatalysts

“…Notably, RuO 2.1 /LDH Td/Oh delivered the best performance with the smallest overpotential of 309 mV at a current density of 10 mA cm –2 ito and R ct value of 3.2 Ω at 1.70 V vs RHE, superior to those of LDH Td/Oh /RuO 2.1 (365 mV, 4.6 Ω) as well as rGO/LDH Td/Oh (322 mV, 3.6 Ω). Moreover, due to the special adsorption or catalytic reaction of the LDH Td/Oh monolayer films in the catalytic process, − impedance spectra for LDH Td/Oh and bilayer films of rGO/LDH Td/Oh , RuO 2.1 /LDH Td/Oh , and LDH Td/Oh /RuO 2.1 display a small induction loop in the low-frequency region. Corresponding equivalent circuit analyses are provided in Figure S9b and Table S5.…”