Boosting Electrocatalytic Oxygen Evolution: Superhydrophilic/Superaerophobic Hierarchical Nanoneedle/Microflower Arrays of Ce_xCo_3–xO₄ with Oxygen Vacancies

Abstract

The oxygen evolution reaction has become the bottleneck of electrochemical water splitting for its sluggish kinetics. Developing high-efficiency and low-cost non-noble-metal oxide electrocatalysts is crucial but challenging for industrial application. Herein, superhydrophilic/superaerophobic hierarchical nanoneedle/microflower arrays of Ce-substituted Co3O4 (Ce x Co3–x O4) in situ grown on the nickel foam are successfully constructed. The hierarchical architecture and superhydrophilic/superaerophobic interface can be facilely regulated by controlling the introduction of Ce into Co3O4. The unique feature of hierarchical architecture and superhydrophilic/superaerophobic interface is in favor of electrolyte penetration and bubbles release. In addition, the presence of oxygen vacancy and Ce endows the catalyst with enhanced intrinsic activity. Benefiting from these advantages, the optimized Ce0.12Co2.88O4 catalyst shows a superior electrocatalytic performance for the oxygen evolution reaction (OER) with an overpotential of 282 mV at 20 mA cm–2, and a Tafel slope of 81.4 mV dec–1. The turnover frequency of 0.0279 s–1 for Ce0.12Co2.88O4 is 9.3 times larger than that for Co3O4 at an overpotential of 350 mV. Moreover, the optimized Ce0.12Co2.88O4 catalyst shows a robust long-term stability in alkaline media.

Iron-doped novel Co-based metal–organic frameworks for preparation of bifunctional catalysts with an amorphous structure for OER/HER in alkaline solution

“…[3][4][5][6] An electrochemical water splitting system is composed of two electron transfer processeshydrogen evolution reaction (HER) at the cathode and four electron transfer processesoxygen evolution reaction (OER) at the anode, which provides a green and sustainable way to produce clean energy hydrogen fuel. [7][8][9][10][11] It has been well documented that two electrodes of the electrolysis system play a significant role in hydrogen production. However, during the practical electrolysis process, a certain overpotential is usually required to overcome the thermodynamic equilibrium potential, resulting in an increase in energy consumption.…”

Engineered Superhydrophilic/Superaerophobic Catalyst: Two-Dimensional Co(OH)2–CeO2 Nanosheets Supported on Three-Dimensional Co Dendrites for Overall Water Splitting

“…Excessive agglomeration of nanosheets would decrease the utilization of active sites and shorten the efficiency of catalysts. Benefiting from the special property of liable coordination with oxygen ligands with high and flexible coordination numbers, Ce ions are easily bonded to hydroxide ions (hard oxygen ligands) as a hard Lewis acid . Hence, Ce ions can hamper the attack from OH – on Co ions as a buffer during electrodeposition, which is in favor of adjusting the growth of the crystal and the morphology of nanosheets.…”

“…20,21 Moreover, Ce ions are hard Lewis acid, which can bond with OH − to slow down the formation of other metal hydroxides, having a positive effect on adjusting the morphology and the crystal growth of metal hydroxides. 16 However, numerous studies have proved that the introduction of CeO 2 in hydroxides only improves the performance of the OER, while in phosphates, nitrides or sulfides can improve the performance of the HER. For instance, Huang and his colleagues accomplished remarkable enhancement of activity and stability in the OER via preparing Ni(OH) 2 /CeO 2 .…”

“…Fewer active sites and poor intrinsic activity caused by a large proportion of base planes were also important reasons for restricting catalytic activity. Hence, some tactics, such as introducing foreign elements and interface engineering, have been applied to enhance the catalytic performance of hydroxide via regulating the electronic structure and modulating the morphology with a larger surface area. , Zhou et al reported that Fe species were adsorbed on Co­(OH) 2 nanosheets, which adjusted the adsorption energy of intermediates and facilitated the growth of active oxyhydroxides (FeOOH/CoOOH) for the OER . Liu et al proposed Co/CoO/Co­(OH) 2 hybrid nanowires with strong chemical couplings .…”

Biomimicry-inspired fish scale-like Ni3N/FeNi3N/NF superhydrophilic/superaerophobic nanoarrays displaying high electrocatalytic performance

“…In turn, this will lead to the deactivation of the active sites on the electrode surface. 7–9 As demonstrated by Iwata et al , 1 the wettability of the catalyst materials being studied can be transformed from superhydrophilic to superhydrophobic by covering the hydrophilic surface with different amounts of polytetrafluoroethylene (PTFE). As a result, different bubble growth and detachment patterns were observed along with the changes in the wettability of the catalysts being studied.…”