Electrodeposited Cobalt Nanosheets on Smooth Silver as a Bifunctional Catalyst for OER and ORR: In Situ Structural and Catalytic Characterization

Abstract

Developing earth-abundant, cost-effective, and active bifunctional electrocatalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is key to boosting sustainable energy systems such as electrolyzers and lithium–air batteries. However, the performance of promising cobalt-based materials is impaired by the external effects of binders and carbon additives as well as inhomogeneous electrode fabrication. In this work, binder- and carbon-free flower-like Co-decorated Ag catalytic nanosheets were in situ-synthesized via a simple electrodeposition approach. The morphology, composition, and structure of Co/Ag before and after OER were characterized using scanning electron microscopy (SEM), energy-dispersive X-ray (EDX), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD). Co/Ag thin film electrodes with various Co contents exhibited a bifunctional activity toward ORR and OER due to a synergistic effect. XPS analysis suggested the formation of Co3O4 as the main active species for OER. In particular, Co (83%)/Ag surface revealed a 60 mV lower ORR overpotential than a pure Ag surface and even lower than drop-casted Co3O4 nanoparticles on Ag surface. Only 1.5% peroxide was generated, suggesting a four-electron transfer ORR. In addition, the OER onset potential on Co/Ag is 60 mV less than Co3O4. Tafel slopes of 71 and 75 mV dec–1 were obtained for ORR and OER, respectively. Importantly, the three-dimensional (3D) growth mechanism of a cobalt layer (∼1 nm) on a well-defined atomic smooth Ag surface is unraveled by in situ electrochemical scanning tunneling microscopy (EC-STM). EC-STM suggests that Co prefers to nucleate at the step edges of Ag and grows in a 3D, forming nanoparticles, where the deposition/dissolution process of the Co adlayer on Ag is reversible. This investigation may provide insights into design strategies of efficient oxygen electrocatalysts.

Dendritic Fe0.64Ni0.36/FeOOH Application for the Decomposition of High-Concentration Alkaline Seawater

“…Comparative XPS analysis of CuNiFe X @CF (X = 0.1, 1, 3 ) catalysts was performed for a more thorough understanding of the effect of Fe content on the electronic structure of catalysts. 50,51 The full spectrum of XPS CuNiFe 1 @CF is shown in Figure S7, which is mainly composed of Fe, Ni, Cu, and O, consistent with EDS elemental analysis. Figure 2e shows the Fe 2p spectrum, and for CuNiFe 1 @CF, two distinct peaks at 718.05 and 732.82 eV match the satellite peaks of Fe 2p 3/2 and 2p 1/2 , respectively.…”

Highly Porous Metal–Organic Framework Entrapped by Cobalt Telluride–Manganese Telluride as an Efficient Bifunctional Electrocatalyst

“…Henceforth, it is essential to develop a dual-purpose catalyst capable of enhancing both the OER and the ORR, resulting in enhanced efficiency of zinc-air batteries . To date, RuO 2 /IrO 2 catalysts have been recognized as highly efficient OER benchmark catalysts, and Pt/C catalysts have been accepted as the benchmark catalysts for the ORR. − However, the high costs, limited catalytic bifunctionality, and poor stability of these noble metal catalysts prevent them from being used commercially on a significant scale in the future . Therefore, it is essential to develop innovative and effective OER/ORR bifunctional electrocatalysts produced from easily available and cost-effective components.…”

Insight into the Anticorrosion Behaviors of Phase-Transformed Cobalt Hydroxides for Long-Term Electrocatalytic Water Oxidation in Saline Electrolytes

“…Cobalt hydroxide has been widely used as an OER catalyst in alkaline environments. − However, it is a precatalyst that experiences phase transformations to the active Co 3+ - or Co 4+ -containing species, such as amorphous Co oxy-hydroxides. , In this regard, extensive studies have been conducted to identify the OER active sites of Co­(OH) 2 both in α- and β-phases. − Nevertheless, the understanding in the structural evolution of Co­(OH) 2 during OER and CER processes is deficient, which is critical for the application and optimization of Co­(OH) 2 for superior catalytic performance in alkaline saline water. Herein, we focus on an electrodeposited α-Co­(OH) 2 on a nickel foam (NF) substrate and investigate the anticorrosion behaviors in alkaline saline electrolytes (1.0 M KOH and 0.5 M NaCl).…”

“…13−17 However, it is a precatalyst that experiences phase transformations to the active Co 3+ -or Co 4+containing species, such as amorphous Co oxy-hydroxides. 18,19 In this regard, extensive studies have been conducted to identify the OER active sites of Co(OH) 2 both in αand β-phases. 20−22 Nevertheless, the understanding in the structural evolution of Co(OH) 2 during OER and CER processes is deficient, which is critical for the application and optimization of Co(OH) 2 for superior catalytic performance in alkaline saline water.…”