Hydrogen production from electrochemical water splitting is a promising route to pursue clean and sustainable energy sources. Here, a three-dimensional nanoporous Cu−Ru alloy is prepared as a high-performance platinum-free catalyst for hydrogen evolution reaction (HER) by a dealloying process. Significantly, the optimized nanoporous alloy Cu 53 Ru 47 exhibits remarkable catalytic activity for HER with nearly zero onset overpotential and ultralow Tafel slopes (∼30 and ∼35 mV dec −1 ) in both alkaline and neutral electrolytes, achieving a catalytic current density of 10 mA cm −2 at low overpotentials of ∼15 and ∼41 mV, respectively. Operando Xray absorption spectroscopy experiments, in conjunction with DFT simulations, reveal that the incorporation of Ru atoms into the Cu matrix not only accelerates the reaction step rates of water adsorption and activation but also optimizes the hydrogen bonding energy on Cu and Ru active sites, improving the intrinsic activity for HER.
Prussian blue analogs with an open framework are ideal cathodes for Na‐ion batteries. A superior high‐rate and highly stable monoclinic nickel hexacyanoferrate (NiHCF‐3) is synthesized via a facile one‐step crystallization‐controlled co‐precipitation method. It gives a high specific capacity of 85.7 mAh g−1, nearly to its theoretical value. It also exhibits an excellent rate capability with a high capacity retention ratio of 78% at 50 C and a stable cycling performance over 1200 cycles. Through the ex situ X‐ray diffraction and pair distribution function measurements, it is found that the monoclinic structure with distorted framework is greatly related to the high Na content. The electronic structure studies by density functional theory (DFT) calculation demonstrate that NiHCF‐3 deformation promotes the framework conductivity and improves the electrochemical activity of Fe, which results in an ultrahigh‐rate performance of monoclinic phase. Furthermore, the high‐quality monoclinic (NiHCF‐3) exhibits excellent compatibility with both hard carbon and NaTi2(PO4)3 anodes in full cells, which shows great prospects for the application in the large‐scale energy storage systems.
Hard
carbon (HC) is one of the most promising anode materials for sodium-ion
batteries (SIBs) due to its suitable potential and high reversible
capacity. At the same time, the correlation between carbon local structure
and sodium-ion storage behavior is not clearly understood. In this
paper, the two series of HC materials with perfect spherical morphology
and tailored microstructures were designed and successfully produced
using resorcinol formaldehyde (RF) resin as precursor. Via hydrothermal
self-assembly and controlled pyrolysis, RF is a flexible precursor
for high-purity carbon with a wide range of local-structure variation.
Using these processes, one series of five representative RF-based
HC nanospheres with varying degrees of graphitization were obtained
from an RF precursor at different carbonization temperatures. The
other series of HC materials with various microscopic carbon layer
lengths and shapes was achieved by carbonizing five RF precursors
with different cross-linking degrees at a single carbonization condition
(1300 °C and 2 h). On the basis of the microstructures, unique
electrochemical characteristics, and atomic pair distribution function
(PDF) analyses, we proposed a new model of “three-phase”
structural for HC materials and found triregion Na-ion storage behavior:
chemi-/physisorption, intercalation between carbon layers, and pore-filling,
derived from the HC phases, respectively. These results enable new
understanding and insight into the sodium storage mechanism in HC
materials and improve the potential for carbon-based SIB anodes.
Prussian blue analogs (PBAs) are especially investigated as superior cathodes for sodium‐ion batteries (SIBs) due to high theoretical capacity (≈170 mA h g−1) with 2‐Na storage and low cost. However, PBAs suffer poor cyclability due to irreversible phase transition in deep charge/discharge states. PBAs also suffer low crystallinity, with considerable [Fe(CN)6] vacancies, and coordinated water in crystal frameworks. Presently, a new chelating agent/surfactant coassisted crystallization method is developed to prepare high‐quality (HQ) ternary‐metal NixCo1−x[Fe(CN)6] PBAs. By introducing inactive metal Ni to suppress capacity fading caused by excessive lattice distortion, these PBAs have tunable limits on depth of charge/discharge. HQ‐NixCo1−x[Fe(CN)6] (x = 0.3) demonstrates the best reversible Na‐storage behavior with a specific capacity of ≈145 mA h g−1 and a remarkably improved cycle performance, with ≈90% capacity retention over 600 cycles at 5 C. Furthermore, a dual‐insertion full cell on the cathode and NaTi2(PO4)3 anode delivers reversible capacity of ≈110 mA h g−1 at a current rate of 1.0 C without capacity fading over 300 cycles, showing promise as a high‐performance SIB for large‐scale energy‐storage systems. The ultrastable cyclability achieved in the lab and explained herein is far beyond that of any previously reported PBA‐based full cells.
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