Enhanced Electrochemical Properties and OER Performances by Cu Substitution in NiCo2O4 Spinel Structure

Abstract

In order to improve the electrochemical performance of the NiCo2O4 material, Ni ions were partially substituted with Cu2+ ions having excellent reducing ability. All of the electrodes were fabricated by growing the Ni1−xCuxCo2O4 electrode spinel-structural active materials onto the graphite felt (GF). Five types of electrodes, NiCo2O4/GF, Ni0.875Cu0.125Co2O4/GF, Ni0.75Cu0.25Co2O4/GF, Ni0.625Cu0.375Co2O4/GF, and Ni0.5Cu0.5Co2O4/GF, were prepared for application to the oxygen evolution reaction (OER). As Cu2+ ions were substituted, the electrochemical performances of the NiCo2O4-based structures were improved, and eventually the OER activities were also greatly increased. In particular, the Ni0.75Cu0.25Co2O4/GF electrode exhibited the best OER activity in a 1.0 M KOH alkaline electrolyte: the cell voltage required to reach a current density of 10 mA cm−2 was only 1.74 V (η = 509 mV), and a low Tafel slope of 119 mV dec−1 was obtained. X-ray photoelectron spectroscopy (XPS) analysis of Ni1−xCuxCo2O4/GF before and after OER revealed that oxygen vacancies are formed around active metals by the insertion of Cu ions, which act as OH-adsorption sites, resulting in high OER activity. Additionally, the stability of the Ni0.75Cu0.25Co2O4/GF electrode was demonstrated through 1000th repeated OER acceleration stability tests with a high faradaic efficiency of 94.3%.

Photocatalytic and Electrocatalytic Properties of Cu-Loaded ZIF-67-Derivatized Bean Sprout-Like Co-TiO2/Ti Nanostructures

“…The onset potential showed no significant difference, with only <+0.02 V when Cu deposition was lower than 120 s. When Cu was deposited for 240 s, 480 s and 960 s, the onset potentials were observed to be +1.57 V, +1.59 V and +1.59 V (vs. RHE), respectively. These are in good agreement with the literature for ZIF-67-derivatized catalysts and Co (and/or Ni) oxide-based catalysts [ 13 , 28 ]. On the basis of the onset potentials (E RHE ) from the LSV curves ( Figure 9 a), the OER overpotential (η) was calculated using η = E RHE −1.23 V [ 11 ].…”

“…CO 2 reduction is a multielectron process, where electrons are either provided by photogeneration or are applied by potential electrochemistry. The generally important mechanism is demonstrated below [ 28 , 45 ]. Co-TiO 2 /Ti + hν → Co-TiO 2 /Ti (VB, h + ) + Co-TiO 2 /Ti (CB, e − ) under UV light H 2 O + h + → OH + H + OH + H 2 O + 3h + → O 2 + 3H + CO 2 + 2H + + 2e − → CO + H 2 O CO 2 + 8H + + 8e − → CH 4 + 2H 2 O CO 2 + 6H + + 6e − → CH 3 OH + H 2 O 2CO 2 + 10H + + 10e − → C 2 H 2 + 4H 2 O …”

“…Therefore, the present study shows some data sets for catalytic performances on CO 2 reduction. ZIP-67 was chosen because Co is in the structure, and consequent Co oxide-based catalysts have potentially high applicability to water splitting reactions [ 28 ]. Cu and Ti were chosen because they have been extensively used as substituent materials and catalyst supports in photocatalysis and electrocatalysis [ 28 , 29 , 30 , 31 , 32 ].…”

“…ZIP-67 was chosen because Co is in the structure, and consequent Co oxide-based catalysts have potentially high applicability to water splitting reactions [ 28 ]. Cu and Ti were chosen because they have been extensively used as substituent materials and catalyst supports in photocatalysis and electrocatalysis [ 28 , 29 , 30 , 31 , 32 ]. Therefore, the present results provide a useful strategy for the design of new catalyst materials with high efficiency for energy and environment fields via CO 2 reduction and water splitting.…”

Effects of Annealing Temperature on the Oxygen Evolution Reaction Activity of Copper–Cobalt Oxide Nanosheets

“…Previous studies were conducted on Cu x Co 2- x O 4 (CCO) catalysts, which have higher conductivities as a result of the Cu doping of Co 3 O 4 . In addition, various approaches such as chemical deposition, hydrothermal methods, and electrodeposition have been used to improve the surface morphology and electrochemical and crystallographic properties of the CCO catalyst [ 22 , 23 ].…”