New insight into the effect of fluorine doping and oxygen vacancies on electrochemical performance of Co 2 MnO 4 for flexible quasi-solid-state asymmetric supercapacitors, Energy Storage Materials (2019),
Developing low‐cost and high‐efficiency catalysts for sustainable hydrogen production through electrocatalytic hydrogen evolution reaction (HER) is crucial yet remains challenging. Here, a strategy is proposed to fill Ni‐vacancy (Niv) sites of dual‐deficient NiO (D‐NiO‐Pt) deliberately created by Ar plasma with homogeneously distributed Pt atoms driven by oxygen vacancies (Ov). The incorporated Pt atoms filling the Niv reduce the formation energy to increase crystal stability, and subsequently combine with additional Ov to tune the electronic structure of the surrounding Ni sites. Thus, a more ideal hydrogen adsorption free energy (ΔGH*) closer to 0 of Ni sites and Pt sites can be achieved. As a result, the D‐NiO‐Pt electrode achieves superior mass activity of ≈1600 mA mg−1 (normalized by platinum) and nearly negligible loss of activity during long‐term operation, which is much better than as‐prepared Pt‐containing NiO catalysts without plasma treatment. A low overpotential of 20 mV is required for the D‐NiO‐Pt at 10 mA cm−2 in alkaline HER, outperforming that of the commercial Pt/C. In addition, the universal access to the other Ni‐based compounds including nickel phosphide (Ni2P), nickel sulfide (Ni0.96S), and nickel selenide (NiSe2) is also demonstrated by employing a vacancy‐driven Pt filling mechanism.
Exploration of proficient electrocatalyst from earth-abundant nonprecious metals in lieu of noble metal-based catalysts to obtain clean hydrogen energy through large-scale electrochemical water splitting is still an ongoing challenge. Herein, iron-doped nickel cobalt phosphide nanoplate arrays grown on a carbon cloth (NiCoFe x P/CC) are fabricated using a simple hydrothermal route, followed by phosphorization. The electrochemical analysis demonstrates that the NiCoFe x P/CC electrode possesses high electrocatalytic activity for water splitting in alkaline medium. Benefits from the synergistic effect between the metal centers, two-dimensional porous nanoplates, and unique threedimensional electrode configuration of NiCoFe x P/CC provide small overpotentials of 39 at 10 mA cm −2 and 275 mV at 50 mA cm −2 to drive the hydrogen evolution reaction and oxygen evolution reaction, respectively. Furthermore, the assembled two-electrode (NiCoFe x P/ CC∥NiCoFe x P/CC) alkaline water electrolyzer can achieve 10 mA cm −2 current density at 1.51 V. Remarkably, it can maintain stable electrolysis over 150 h. The excellent activity and stability of this catalyst is proved to be a economical substitute of commercial noble metal-based catalysts in technologies relevant to renewable energy.
A highly effective electrothermal tuning method is demonstrated for Al–SiC nanomechanical
resonators. Doubly clamped beam devices are actuated and read out using a
magnetomotive technique under a moderate vacuum at room temperature. Direct current
applied to a beam heats the structure and shifts the resonance frequency downward.
Frequency shifts of 10% are easily achievable, and the thermal time constant
of these structures is in the submicrosecond range. The initial frequency and
frequency tunability are studied for beams of varying Al thickness, and the device
performance can be accurately modelled using simple mechanical and thermal
models. Because of the different mechanical properties of SiC and Al, both the
initial frequency and the frequency tunability can be modified by varying the Al
layer thickness. This approach has the potential to become an important tool for
effective frequency tuning in deployable SiC-based nanoelectromechanical system
devices and systems for applications that would benefit from SiC as the structural
material.
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