Time-Frequency Analysis Based on Improved Variational Mode Decomposition and Teager Energy Operator for Rotor System Fault Diagnosis

A time-frequency analysis method based on improved variational mode decomposition and Teager energy operator (IVMD-TEO) is proposed for fault diagnosis of turbine rotor. Variational mode decomposition (VMD) can decompose a multicomponent signal into a number of band-limited monocomponent signals and can effectively avoid model mixing. To determine the number of monocomponents adaptively, VMD is improved using the correlation coefficient criterion. Firstly, IVMD algorithm is used to decompose a multicomponent signal into a number of monocompositions adaptively. Second, all the monocomponent signals’ instantaneous amplitude and instantaneous frequency are demodulated via TEO, respectively, because TEO has fast and high precision demodulation advantages to monocomponent signal. Finally, the time-frequency representation of original signal is exhibited by superposing the time-frequency representations of all the monocomponents. The analysis results of simulation signal and experimental turbine rotor in rising speed condition demonstrate that the proposed method has perfect multicomponent signal decomposition capacity and good time-frequency expression. It is a promising time-frequency analysis method for rotor fault diagnosis

Development of solar fuels photoanodes through combinatorial integration of Ni-La-Co-Ce oxide and Ni-Fe-Co-Ce oxide catalysts on BiVO_4

The development of an efficient, stable photoanode to provide protons and electrons to the (photo)cathode remains a primary materials challenge in the establishment of a scalable technol. for solar fuels generation. The typical photoanode architecture consists of a semiconductor light absorber coated with a metal oxide that serves a combination of functions, including corrosion protection, electrocatalysis, light trapping, hole transport, and elimination of deleterious recombination sites. To provide a more efficient exploration of metal oxide coatings for a given light absorber, we introduce a high throughput methodol. wherein a uniform BiVO_4 library is coated with 858 unique metal oxides covering a range of metal oxide loadings and the full Ni-La-Co-Ce oxide or Ni-Fe-Co-Ce oxide psuedo-quaternary compn. spaces. Photoelectrochem. characterization of each photoanode reveals that approx. one third of the coatings lower the photoanode performance while select combinations of metal oxide compn. and loading provide up to a 14-fold increase in the max. photoelectrochem. power generation for oxygen evolution in pH 13 electrolyte. Particular Ce-rich coatings also exhibit an anti-reflection effect that further amplifies the performance, yielding a 20-fold enhancement in power conversion efficiency compared to bare BiVO_4. By use of in situ optical spectroscopy and comparisons between the metal oxide coatings and their extrinsic optical and electrocatalytic properties, we present a suite of data-driven discoveries, including compn. regions which form optimal interfaces with BiVO_4 and photoanodes that are suitable for integration with a photocathode due to their excellent power conversion and solar transmission efficiencies. The initial high throughput discoveries were extended and validated through follow-up high throughput investigations and conventional photoelectrochem. measurements. The high throughput experimentation and informatics provides a powerful platform for both identifying the pertinent interfaces for further study and discovering high performance photoanodes for incorporation into efficient water splitting devices

Correlating Oxidation State and Surface Area to Activity from Operando Studies of Copper CO Electroreduction Catalysts in a Gas-fed Device

The rational design of high-performance electrocatalysts requires a detailed understanding of dynamic changes in catalyst properties, including oxidation states, surface area, and morphology under realistic working conditions. Oxide-derived Cu catalysts exhibit a remarkable selectivity toward multicarbon products for the electrochemical CO reduction reaction (CORR), but the exact role of the oxide remains elusive for explaining the performance enhancements. Here, we used operando X-ray absorption spectroscopy (XAS) coupled with simultaneous measurements of the catalyst activity and selectivity by gas chromatography (GC) to study the relationship between oxidation states of Cu-based catalysts and the activity for ethylene (C₂H₄) production in a CO gas-fed cell. By utilizing a custom-built XAS cell, oxidation states of Cu catalysts can be probed in device-relevant settings and under high current densities (>80 mA cm⁻²) for the CORR. By employing an electrochemical oxidation process, we found that the Cu oxidation states and specific ion species do not correlate with C₂H₄ production. The difference in the CORR activity is also investigated in relation to electrochemical surface area (ECSA) changes. While the hydrogen evolution reaction (HER) activity is positively correlated to the ECSA changes, the increased C₂H₄ activity is not proportional to the ECSA. Ex situ characterization from microscopic techniques suggests that the changes in the C₂H₄ activity and selectivity may arise from a morphological transformation that evolves into a more active structure. These comprehensive results give rise to the development of a cell regeneration method that can restore the performance of the Cu catalyst without cell disassembly. Our study establishes a basis for the rational design of highly active electrocatalysts for broad-range reactions in a gas-fed device

Development of solar fuels photoanodes through combinatorial integration of Ni-La-Co-Ce oxide and Ni-Fe-Co-Ce oxide catalysts on BiVO_4

The development of an efficient, stable photoanode to provide protons and electrons to the (photo)cathode remains a primary materials challenge in the establishment of a scalable technol. for solar fuels generation. The typical photoanode architecture consists of a semiconductor light absorber coated with a metal oxide that serves a combination of functions, including corrosion protection, electrocatalysis, light trapping, hole transport, and elimination of deleterious recombination sites. To provide a more efficient exploration of metal oxide coatings for a given light absorber, we introduce a high throughput methodol. wherein a uniform BiVO_4 library is coated with 858 unique metal oxides covering a range of metal oxide loadings and the full Ni-La-Co-Ce oxide or Ni-Fe-Co-Ce oxide psuedo-quaternary compn. spaces. Photoelectrochem. characterization of each photoanode reveals that approx. one third of the coatings lower the photoanode performance while select combinations of metal oxide compn. and loading provide up to a 14-fold increase in the max. photoelectrochem. power generation for oxygen evolution in pH 13 electrolyte. Particular Ce-rich coatings also exhibit an anti-reflection effect that further amplifies the performance, yielding a 20-fold enhancement in power conversion efficiency compared to bare BiVO_4. By use of in situ optical spectroscopy and comparisons between the metal oxide coatings and their extrinsic optical and electrocatalytic properties, we present a suite of data-driven discoveries, including compn. regions which form optimal interfaces with BiVO_4 and photoanodes that are suitable for integration with a photocathode due to their excellent power conversion and solar transmission efficiencies. The initial high throughput discoveries were extended and validated through follow-up high throughput investigations and conventional photoelectrochem. measurements. The high throughput experimentation and informatics provides a powerful platform for both identifying the pertinent interfaces for further study and discovering high performance photoanodes for incorporation into efficient water splitting devices

Discovery of Fe–Ce Oxide/BiVO_4 Photoanodes through Combinatorial Exploration of Ni–Fe–Co–Ce Oxide Coatings

An efficient photoanode is a prerequisite for a viable solar fuels technology. The challenges to realizing an efficient photoanode include the integration of a semiconductor light absorber and a metal oxide electrocatalyst to optimize corrosion protection, light trapping, hole transport, and photocarrier recombination sites. To efficiently explore metal oxide coatings, we employ a high-throughput methodology wherein a uniform BiVO_4 film is coated with 858 unique metal oxide coatings covering a range of metal oxide loadings and the full (Ni–Fe–Co–Ce)O_x pseudoquaternary composition space. Photoelectrochemical characterization of the photoanodes reveals that specific combinations of metal oxide composition and loading provide up to a 13-fold increase in the maximum photoelectrochemical power generation for oxygen evolution in pH 13 electrolyte. Through mining of the high-throughput data we identify composition regions that form improved interfaces with BiVO_4. Of particular note, integrated photoanodes with catalyst compositions in the range Fe_((0.4–0.6))Ce_((0.6–0.4))O_x exhibit high interface quality and excellent photoelectrochemical power conversion. Scaled-up inkjet-printed electrodes and photoanodic electrodeposition of this composition on BiVO_4 confirms the discovery and the synthesis-independent interface improvement of (Fe–Ce)O_x coatings on BiVO_4

Interface engineering for light-driven water oxidation: unravelling the passivating and catalytic mechanism in BiVO_4 overlayers

Artificial photosynthetic approaches require the combination of light absorbers interfaced with overlayers that enhance charge transport and collection to perform catalytic reactions. Despite numerous efforts that have coupled various catalysts to light absorbing semiconductors, the optimization of semiconductor/catalyst as well as catalyst/electrolyte interfaces and the identification of the role of the catalyst still remain a key challenge. Herein, we assemble (NiFeCoCe)O_x multi-component overlayers, interfaced with bismuth vanadate photoanodes, and determine the roles of different elements on promoting interfacial charge transfer and catalytic reaction over competitive photocarrier recombination loss processes. Through this understanding, and aided by complementary macroscopic photoelectrochemical measurements and nanoscale atomic force microscopy techniques, a bifunctional (CoFeCe/NiFe)O_x overlayer was rationally engineered. The resulting multi-functional coating yields BiVO_4 photoanodes with almost 100% efficient surface collection of holes under oxygen evolving reaction conditions. The (CoFeCe)O_x component excels at efficient capture and transport of photogenerated holes in BiVO_4 through the availability of redox active states, whereas (NiFe)O_x plays a vital role in reducing charge recombination at the BiVO_4/electrolyte interface. In addition, this study supports the hypothesis that catalytic sites act as electronically active trap states on uncoated BiVO_4 photoanodes

Interface engineering for light-driven water oxidation: unravelling the passivating and catalytic mechanism in BiVO_4 overlayers

Artificial photosynthetic approaches require the combination of light absorbers interfaced with overlayers that enhance charge transport and collection to perform catalytic reactions. Despite numerous efforts that have coupled various catalysts to light absorbing semiconductors, the optimization of semiconductor/catalyst as well as catalyst/electrolyte interfaces and the identification of the role of the catalyst still remain a key challenge. Herein, we assemble (NiFeCoCe)O_x multi-component overlayers, interfaced with bismuth vanadate photoanodes, and determine the roles of different elements on promoting interfacial charge transfer and catalytic reaction over competitive photocarrier recombination loss processes. Through this understanding, and aided by complementary macroscopic photoelectrochemical measurements and nanoscale atomic force microscopy techniques, a bifunctional (CoFeCe/NiFe)O_x overlayer was rationally engineered. The resulting multi-functional coating yields BiVO_4 photoanodes with almost 100% efficient surface collection of holes under oxygen evolving reaction conditions. The (CoFeCe)O_x component excels at efficient capture and transport of photogenerated holes in BiVO_4 through the availability of redox active states, whereas (NiFe)O_x plays a vital role in reducing charge recombination at the BiVO_4/electrolyte interface. In addition, this study supports the hypothesis that catalytic sites act as electronically active trap states on uncoated BiVO_4 photoanodes

Bi-containing n-FeWO_4 Thin Films Provide the Largest Photovoltage and Highest Stability for a sub-2 eV Band Gap Photoanode

Photoelectrocatalysis of the oxygen evolution reaction remains a primary challenge for development of tandem-absorber solar fuel generators due to the lack of a photoanode with broad solar spectrum utilization, a large photovoltage, and stable operation. Bismuth vanadate with a 2.4–2.5 eV band gap has shown the most promise becauses its photoactivity down to 0.4 V vs RHE is sufficiently low to couple to a lower-gap photocathode for fuel synthesis. Through development of photoanodes based on the FeWO_4 structure, in particular, Fe-rich variants with addition of about 6% Bi, we demonstrate the same 0.4 V vs RHE turn-on voltage with a 2 eV band gap metal oxide, enabling a 2-fold increase in the device efficiency limit. Combinatorial exploration of materials composition and processing facilitated synthesis of n-type variants of this typical p-type semiconductor that exhibit much higher photoactivity than previous implementations of FeWO_4 in solar photochemistry. The photoanodes are particularly promising for solar fuel applications given their stable operation in acid and base