scholarly journals In Situ EPR Characterization of a Cobalt Oxide Water Oxidation Catalyst at Neutral pH

Catalysts ◽  
2019 ◽  
Vol 9 (11) ◽  
pp. 926 ◽  
Author(s):  
Yury Kutin ◽  
Nicholas Cox ◽  
Wolfgang Lubitz ◽  
Alexander Schnegg ◽  
Olaf Rüdiger

Here we report an in situ electron paramagnetic resonance (EPR) study of a low-cost, high-stability cobalt oxide electrodeposited material (Co-Pi) that oxidizes water at neutral pH and low over-potential, representing a promising system for future large-scale water splitting applications. Using CW X-band EPR we can follow the film formation from a Co(NO3)2 solution in phosphate buffer and quantify Co uptake into the catalytic film. As deposited, the film shows predominantly a Co(II) EPR signal, which converts into a Co(IV) signal as the electrode potential is increased. A purpose-built spectroelectrochemical cell allowed us to quantify the extent of Co(II) to Co(IV) conversion as a function of potential bias under operating conditions. Consistent with its role as an intermediate, Co(IV) is formed at potentials commensurate with electrocatalytic O2 evolution (+1.2 V, vs. SHE). The EPR resonance position of the Co(IV) species shifts to higher fields as the potential is increased above 1.2 V. Such a shift of the Co(IV) signal may be assigned to changes in the local Co structure, displaying a more distorted ligand field or more ligand radical character, suggesting it is this subset of sites that represents the catalytically ‘active’ component. The described spectroelectrochemical approach provides new information on catalyst function and reaction pathways of water oxidation.

2021 ◽  
Author(s):  
Xueli Zheng ◽  
Jing Tang ◽  
Alessandro Gallo ◽  
Jose Antonio Garrido Torres ◽  
Xiaoyun Yu ◽  
...  

<p>The efficiency of the synthesis of renewable fuels and feedstocks from electrical sources is limited at present by the sluggish water oxidation reaction. Single atom catalysts (SACs) with a controllable coordination environment and exceptional atom utilization efficiency open new paradigms towards designing high performance water oxidation catalysts. Here, using<i> operando</i> X-ray absorption spectroscopy measurements with calculations of spectra and electrochemical activity, we demonstrate that the origin of water oxidation activity of IrNiFe SACs is the presence of highly oxidized Ir single atom (Ir<sup>5.3+</sup>)<sup> </sup>in the NiFe oxyhydroxide under operating conditions. We show that the optimal water oxidation catalyst could be achieved by systematically increasing the oxidation state and modulating the coordination environments of the Ir active sites anchored atop the NiFe oxyhydroxide layers. Based on the proposed mechanism, we have successfully anchored Ir single-atom sites on NiFe oxyhydroxides (Ir<sub>0.1</sub>/Ni<sub>9</sub>Fe SAC) via a unique<i> in situ</i> cryogenic photochemical reduction (<i>in situ</i> Cryo-PCR) method which delivers an overpotential of 183 millivolts at 10 milliamperes per square centimeter and retains its performance following 20 hours of operation in 1 M KOH electrolyte, outperforming the reported catalysts and the commercial IrO<sub>2</sub> catalysts. These findings open the avenue towards atomic-level understanding of oxygen evolution of catalytic centers under <i>in operando</i> condition.</p>


2021 ◽  
Author(s):  
Xueli Zheng ◽  
Jing Tang ◽  
Alessandro Gallo ◽  
Jose Antonio Garrido Torres ◽  
Xiaoyun Yu ◽  
...  

<p>The efficiency of the synthesis of renewable fuels and feedstocks from electrical sources is limited at present by the sluggish water oxidation reaction. Single atom catalysts (SACs) with a controllable coordination environment and exceptional atom utilization efficiency open new paradigms towards designing high performance water oxidation catalysts. Here, using<i> operando</i> X-ray absorption spectroscopy measurements with calculations of spectra and electrochemical activity, we demonstrate that the origin of water oxidation activity of IrNiFe SACs is the presence of highly oxidized Ir single atom (Ir<sup>5.3+</sup>)<sup> </sup>in the NiFe oxyhydroxide under operating conditions. We show that the optimal water oxidation catalyst could be achieved by systematically increasing the oxidation state and modulating the coordination environments of the Ir active sites anchored atop the NiFe oxyhydroxide layers. Based on the proposed mechanism, we have successfully anchored Ir single-atom sites on NiFe oxyhydroxides (Ir<sub>0.1</sub>/Ni<sub>9</sub>Fe SAC) via a unique<i> in situ</i> cryogenic photochemical reduction (<i>in situ</i> Cryo-PCR) method which delivers an overpotential of 183 millivolts at 10 milliamperes per square centimeter and retains its performance following 20 hours of operation in 1 M KOH electrolyte, outperforming the reported catalysts and the commercial IrO<sub>2</sub> catalysts. These findings open the avenue towards atomic-level understanding of oxygen evolution of catalytic centers under <i>in operando</i> condition.</p>


Meccanica ◽  
2021 ◽  
Vol 56 (5) ◽  
pp. 1223-1237
Author(s):  
Giacomo Moretti ◽  
Andrea Scialò ◽  
Giovanni Malara ◽  
Giovanni Gerardo Muscolo ◽  
Felice Arena ◽  
...  

AbstractDielectric elastomer generators (DEGs) are soft electrostatic generators based on low-cost electroactive polymer materials. These devices have attracted the attention of the marine energy community as a promising solution to implement economically viable wave energy converters (WECs). This paper introduces a hardware-in-the-loop (HIL) simulation framework for a class of WECs that combines the concept of the oscillating water columns (OWCs) with the DEGs. The proposed HIL system replicates in a laboratory environment the realistic operating conditions of an OWC/DEG plant, while drastically reducing the experimental burden compared to wave tank or sea tests. The HIL simulator is driven by a closed-loop real-time hydrodynamic model that is based on a novel coupling criterion which allows rendering a realistic dynamic response for a diversity of scenarios, including large scale DEG plants, whose dimensions and topologies are largely different from those available in the HIL setup. A case study is also introduced, which simulates the application of DEGs on an OWC plant installed in a mild real sea laboratory test-site. Comparisons with available real sea-test data demonstrated the ability of the HIL setup to effectively replicate a realistic operating scenario. The insights gathered on the promising performance of the analysed OWC/DEG systems pave the way to pursue further sea trials in the future.


2021 ◽  
Author(s):  
Xianzhong Yang ◽  
Chao Li ◽  
Zhongti Sun ◽  
Shuai Yang ◽  
Zixiong Shi ◽  
...  

Abstract Zn metal anode has garnered growing scientific and industrial interest owing to its appropriate redox potential, low cost and good safety. Nevertheless, the instability of Zn metal, caused by dendrite formation, hydrogen evolution and side reactions, gives rise to poor electrochemical stability and unsatisfactory cycling life, greatly hampering large-scale utilization. Herein, an in-situ grown ZnSe layer with controllable thickness is crafted over one side of commercial Zn foil via chemical vapor deposition, aiming to achieve optimized interfacial manipulation between aqueous electrolyte/Zn anode. Thus-derived ZnSe overlayer not only prevents water penetration and restricts Zn2+ two-dimensional diffusion, but also homogenizes the electric field at the interface and facilitates favorable (002) plane growth of Zn. As a result, dendrite-free and homogeneous Zn deposition is obtained; side reactions are concurrently inhibited. In consequence, a high Coulombic efficiency of 99.2% and high cyclic stability for 860 cycles at 1.0 mA cm–2 in symmetrical cells is harvested. Meanwhile, when paired with V2O5 cathode, assembled full cell achieves an outstanding initial capacity (200 mAh g–1) and elongated lifespan (a capacity retention of 84% after 1000 cycles) at 5.0 A g–1. Our highly reversible Zn anode enabled by the interfacial manipulation strategy is anticipated to satisfy the demand of industrial and commercial use.


2019 ◽  
Vol 55 (12) ◽  
pp. 1797-1800 ◽  
Author(s):  
Xuqiang Ji ◽  
Yujia He ◽  
Jingquan Liu

Amorphous cobalt oxide on carbon cloth (AMO-CoO/CC) was prepared as an excellent water-oxidation catalyst with 50 mV less overpotential at 10 mA cm−2 than highly-crystallized Co3O4 in 1.0 M KOH.


2019 ◽  
Vol 116 (22) ◽  
pp. 10658-10663 ◽  
Author(s):  
Ziyuan Song ◽  
Hailin Fu ◽  
Jiang Wang ◽  
Jingshu Hui ◽  
Tianrui Xue ◽  
...  

Ribozymes synthesize proteins in a highly regulated local environment to minimize side reactions caused by various competing species. In contrast, it is challenging to prepare synthetic polypeptides from the polymerization of N-carboxyanhydrides (NCAs) in the presence of water and impurities, which induce monomer degradations and chain terminations, respectively. Inspired by natural protein synthesis, we herein report the preparation of well-defined polypeptides in the presence of competing species, by using a water/dichloromethane biphasic system with macroinitiators anchored at the interface. The impurities are extracted into the aqueous phase in situ, and the localized macroinitiators allow for NCA polymerization at a rate which outpaces water-induced side reactions. Our polymerization strategy streamlines the process from amino acids toward high molecular weight polypeptides with low dispersity by circumventing the tedious NCA purification and the demands for air-free conditions, enabling low-cost, large-scale production of polypeptides that has potential to change the paradigm of polypeptide-based biomaterials.


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