Synergistic effects in bimetallic Pd–CoO electrocatalytic thin films for oxygen evolution reaction

Abstract

Bimetallic catalysts due to the synergistic effects often outperform their single-component counterparts while exhibiting structure and composition-dependent enhancement in active sites, thereby having the potential to improve the current density and over-potential parameters in the water oxidation reaction. Herein, we demonstrate a simple and rapid, yet highly efficient method to fabricate Pd-CoO films of immaculate homogeneity as characterized using different imaging and spectroscopic techniques. The SEM images revealed that the films were composed of bimetallic spherical granules wherein both metals were uniformly distributed in an atomic ratio of ~ 1:1. The time-dependent investigations of the film fabrication behavior demonstrated that the films formed in shorter deposition times (1-2 h) display more porous character, allowing better access to the reaction centers. This character was transcribed into their enhanced electrocatalytic performance toward the oxygen evolution reaction (OER). Using this specific bimetallic formulation, we could attain a low over-potential of 274 mV for a current density of 10 mA cm −2 , whereas the high current density value of > 200 mA cm −2 was achieved while still under 600 mV of over-potential. The cycling and current generation stability was also found to be sufficiently high, which can only be attributed to the facile electron transfer processes and a higher number of active sites available in homogeneous bimetallic films. Electrocatalytic water oxidation is an extensively studied reaction due to its importance in industrial water splitting for hydrogen-based economy 1. Such a non-reliance on fossil fuels can enforce a change towards a more sustainable society with a lesser burden of pollution on the climate. However, this anodic reaction is a limiting factor in the large scale electrolysis of water 2. The process includes four proton-coupled electron transfers and two oxygen atoms bonding together, making it electrochemically sluggish because of high energy demands 3. The result is the high over-potentials, and low current densities, whereas the target is to achieve an industrial standard current density of more than 100 mA cm −2 with the least over-potential possible 4. Thus, the materials with the ability to catalyze this reaction are of high significance not only for water splitting based hydrogen generation 5,6 , but also for oxygen evolution reactions (OER) in metal-air batteries 7,8 , or other oxidation reactions such as the oxidation of CO 9 for the purification of hydrogen fuel obtained via currently accustomed fossil fuels based production. While the oxides of Iridium and Ruthenium still remains the benchmark in catalyzing this process 10 , the search for the earth-abundant low-cost substitute continues 5,11. An illustrative outcome of this search is the oxides of transition metals (e.g., Ni, Co, Fe) showing structures and compositions similar to the active center of spinels or other oxygen-evolving complexes 12-14. From these materials, the oxides of cobalt, espec...

Synergistically Driven CoCr-LDH@VNiS2 as a Bifunctional Electrocatalyst for Overall Water Splitting and Flexible Supercapacitors

“…Meanwhile, CoCr-LDH, VNiS 2 , and Pt/c need overpotentials of 253, 123, and 25 mV at the current density of 10 mA cm –2 , respectively. A Tafel slope of 77 mV dec –1 is achieved for CoCr-LDH@VNiS 2 , which is the lowest compared to CoCr-LDH (180 mV dec –1 ) and VNiS 2 (118 mV dec –1 ), demonstrating fast kinetic performance for HER due to the synergistic effect, , shown in Figure b. To gain insights into the kinetic reaction on an electrode surface, electrochemical impedance spectroscopy (EIS) was performed.…”

High‐Performance Bifunctional Ni−Fe−S Catalyst in situ Synthesized within Graphite Intergranular Nanopores for Overall Water Splitting

“…The cell voltage is generally 1.8–2.4 V to yield a relatively high current density of 200–400 mA cm −2 in industrial water electrolysis [8,19] . It is difficult for a single bifunctional catalyst to possess water electrolysis activity and durability exceeding the industrial catalyst counterparts at the current densities higher than 200 mA cm −2 .…”

“…However, it is a big challenge for a bifunctional catalyst to simultaneously and efficiently catalyze both HER and OER in a single electrolyte at high current densities. This leads to the difficulty for a single catalyst to meet the requirements of industrial water electrolysis that generally operates at 200–400 mA cm −2 under a relatively low cell voltage of 1.8–2.4 V [8] . Additionally, the bifunctional catalysts work in both the HER and OER potential ranges, therefore the initial catalysts probably undergo redox transformations to different active species that deserve more attention [9] …”

Distortion-Induced Interfacial Charge Transfer at Single Cobalt Atom Secured on Ordered Intermetallic Surface Enhances Pure Oxygen Production

“…Conductive supports like N-doped graphitic carbon have been reportedly used with Co oxides like CoO/NGHSs provide high ECSA and electrical conductivity, Fe 3 O 4 /CoO CNTs has high durability and increased number of active sites, and so on. Constructing synergistic interfaces of cobalt oxides and highly active metals like Pt, Pd, and Au/Ag can provide conductivity and stability due to enhanced charge transfer at longer periods of electrocatalysis. , There are reports where a dual-phase system of Co oxides with active metals enhanced stability, like, Ag 2 O–Co 3 O 4 framework obtained from Ag–Co bimetallic, Pd/CoO x for enhanced CO oxidation, MOF-templated Pd/PdO-Co 3 O 4 , N-doped C-nanofiber-Co/CoO x -Pd nanoparticles for enhanced HER and OER, and CoO/Pd(100) derived from Pd–Co bimetallic compound have provided high conductivity due to electron tunneling from the active metal to the Co-oxide species . Also, in CeO x /CoO x , the Ce atoms promote facile formation of CoOOH and optimize binding energies of the OER intermediates .…”