Issue 19, 2020

The HER/OER mechanistic study of an FeCoNi-based electrocatalyst for alkaline water splitting

Abstract

Herein, the electrodeposited-film electrode CFeCoNiP was fabricated to serve as a bifunctional electrocatalyst for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Kinetic Tafel slope analysis suggests that the HER follows the Volmer–Tafel mechanism (29 mV dec−1), indicating that the recombination of the two adsorbed hydrogen atoms is the rate-determining step. The FeCoNi-based thick film (thickness: 168.3 μm) shows a metallic state favorable for electron transfer; on the other hand, in the case of the FeCoNi-based thin film (thickness: 389.2 nm), the in operando XAS investigation reveals that Fe3+-assisted water dissociation promotes the formation of Co2+–μ-H–Ni3+ (catalyst-Had) species, which subsequently undergoes reductive elimination to furnish H2 gas via the HER process. During the OER, the CoNi–oxide matrix acts as a chemical and electroconductive host to build/stabilize the key intermediate [Fe4+[double bond, length as m-dash]O/Fe3+–O˙] motifs; this subsequently triggers the catalytic O–O bond formation (30 mV dec−1) through the radical–radical coupling of the adjacent [Fe4+[double bond, length as m-dash]O/Fe3+–O˙] motifs or/and OH attack on the Fe4+-induced electrophilic oxygen center, leading to the release of O2. The mechanistic experiments provide advanced insights into the catalytic kinetics/intermediates and demonstrate that the electronically cooperative interplay among Fe/Co/Ni leads to enhanced alkaline water electrolysis. The CFeCoNiP catalyst exhibits an excellent HER activity (specific activity js = 0.227 mA cm−2) with a low charge transfer resistance (3.9 Ω) and an overpotential of 37 mV, achieving the current density of 10 mA cm2; moreover, it shows good OER activity (js = 1.798 mA cm−2) with low charge transfer resistance (2.1 Ω) and an overpotential of 250 mV, approaching a current density of 10 mA cm−2 in a 1 M NaOH aqueous solution. The CFeCoNiP/NF (electrodeposited on Ni foam) electrode-pair device achieved the current densities of 100 and 500 mA cm−2 at the voltages of 1.65 and 1.86 V, respectively, under alkaline conditions.

Graphical abstract: The HER/OER mechanistic study of an FeCoNi-based electrocatalyst for alkaline water splitting

Supplementary files

Article information

Article type
Paper
Submitted
17 feb. 2020
Accepted
16 apr. 2020
First published
17 apr. 2020

J. Mater. Chem. A, 2020,8, 9939-9950

The HER/OER mechanistic study of an FeCoNi-based electrocatalyst for alkaline water splitting

F. Tsai, Y. Deng, C. Pao, J. Chen, J. Lee, K. Lai and W. Liaw, J. Mater. Chem. A, 2020, 8, 9939 DOI: 10.1039/D0TA01877E

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