\u3cem\u3eIn Situ\u3c/em\u3e Activated Co\u3csub\u3e3–x\u3c/sub\u3eNi\u3csub\u3ex\u3c/sub\u3eO\u3csub\u3e4\u3c/sub\u3e as a Highly Active and Ultrastable Electrocatalyst for Hydrogen Generation

The spinel Co3O4 has emerged as a promising alternative to noble-metal-based electrocatalysts for electrochemical water electrolysis in alkaline medium. However, pure Co3O4, despite having high activity in anodic water oxidation, remains inactive toward the hydrogen evolution reaction (HER). Here, a Ni-doped Co3O4(Co3–xNixO4) prepared by a simple method exhibits favorable HER activity and stability (\u3e300 h, whether in 1 M KOH or the realistic 30 wt % KOH solution) after in situ electrochemical activation, outperforming almost all of the oxide-based electrocatalysts. More importantly, using the combination of in situ Raman spectroscopy and multiple high-resolution electron microscopy techniques, it is identified that the surface of Co3–xNixO4 crystals is reduced into intertwined CoyNi1–yO nanoparticles with highly exposed {110} reactive planes. Density functional theory calculations further prove that the Ni-doped CoO component in CoyNi1–yO plays a major role during the alkaline HER, because the introduction of Ni atoms into Co–O octahedra can optimize the electrical conductivity and tailor the adsorption/desorption free energies of Had and OHad intermediates

Ultrafast Hole Trapping and Relaxation Dynamics in p-Type CuS Nanodisks

CuS nanocrystals are potential materials for developing low-cost solar energy conversion devices. Understanding the underlying dynamics of photoinduced carriers in CuS nanocrystals is essential to improve their performance in these devices. In this work, we investigated the photoinduced hole dynamics in CuS nanodisks (NDs) using the combination of transient optical (OTA) and X-ray (XTA) absorption spectroscopy. OTA results show that the broad transient absorption in the visible region is attributed to the photoinduced hot and trapped holes. The hole trapping process occurs on a subpicosecond time scale, followed by carrier recombination (~100 ps). The nature of the hole trapping sites, revealed by XTA, is characteristic of S or organic ligands on the surface of CuS NDs. These results not only suggest the possibility to control the hole dynamics by tuning the surface chemistry of CuS but also represent the first time observation of hole dynamics in semiconductor nanocrystals using XTA

Effective Construction of High-quality Iron Oxy-hydroxides and Co-doped Iron Oxy-hydroxides Nanostructures: Towards the Promising Oxygen Evolution Reaction Application

Rational design of high efficient and low cost electrocatalysts for oxygen evolution reaction (OER) plays an important role in water splitting. Herein, a general gelatin-assisted wet chemistry method is employed to fabricate well-defined iron oxy-hydroxides and transitional metal doped iron oxyhydroxides nanomaterials, which show good catalytic performances for OER. Specifically, the Co-doped iron oxy-hydroxides (Co0.54Fe0.46OOH) show the excellent electrocatalytic performance for OER with an onset potential of 1.52 V, tafel slope of 47 mV/dec and outstanding stability. The ultrahigh oxygen evolution activity and strong durability, with superior performance in comparison to the pure iron oxyhydroxide (FeOOH) catalysts, originate from the branch structure of Co0.54Fe0.46OOH on its surface so as to provide many active edge sites, enhanced mass/ charge transport capability, easy release oxygen gas bubbles, and strong structural stability, which are advantageous for OER. Meanwhile, Co-doping in FeOOH nanostructures constitutes a desirable four-electron pathway for reversible oxygen evolution and reduction, which is potentially useful for rechargeable metal-air batteries, regenerative fuel cells, and other important clean energy devices. This work may provide a new insight into constructing the promising water oxidation catalysts for practical clean energy application.Xi'an Jiaotong University; Central Universities [2015qngz12]; China National Funds for Excellent Young Scientists [21522106]; NSFC [21371140, 21571089]This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

Hybrids of Cobalt/Iron Phosphides Derived from Bimetal–Organic Frameworks as Highly Efficient Electrocatalysts for Oxygen Evolution Reaction

The electrochemical splitting of water, as an efficient and large-scale method to produce H₂, is still hindered by the sluggish kinetics of the oxygen evolution reaction (OER) at the anode. Considering the synergetic effect of the different metal sites with coordination on the surface of electrocatalysts, the hybrids of Co/Fe phosphides (denoted as Co-Fe-P) is prepared by one-step phosphorization of CoFe metal–organic frameworks for the first time as highly efficient electrocatalysts for OER. Benefiting from the synergistic effect of Co and Fe, the high valence of Co ions induced by strongly electronegative P and N and the large electrochemical active surface area (ECSA) originated from exposed nanowires on the surface of Co/Fe phosphides, the resultant Co-Fe-P-1.7 exhibits remarkable electrocatalytic performances for OER in 1.0 M KOH, affording an overpotential as low as 244 mV at a current density of 10 mA/cm², a small Tafel slope of 58 mV/dec, and good stability, which is superior to that of the state-of-the-art OER electrocatalysts. In addition, the two-electrode cell with Co-Fe-P-1.7 modified Ni foam as anode and cathode in an alkaline electrolyte, respectively, exhibits the decomposition potential of ca. 1.60 V at a current density of 10 mA/cm² and excellent stability

Bimetallic Nickel Cobalt Sulfide as Efficient Electrocatalyst for Zn–Air Battery and Water Splitting

Abstract The development of efficient earth-abundant electrocatalysts for oxygen reduction, oxygen evolution, and hydrogen evolution reactions (ORR, OER, and HER) is important for future energy conversion and energy storage devices, for which both rechargeable Zn–air batteries and water splitting have raised great expectations. Herein, we report a single-phase bimetallic nickel cobalt sulfide ((Ni,Co)S2) as an efficient electrocatalyst for both OER and ORR. Owing to the synergistic combination of Ni and Co, the (Ni,Co)S2 exhibits superior electrocatalytic performance for ORR, OER, and HER in an alkaline electrolyte, and the first principle calculation results indicate that the reaction of an adsorbed O atom with a H2O molecule to form a *OOH is the potential limiting step in the OER. Importantly, it could be utilized as an advanced air electrode material in Zn–air batteries, which shows an enhanced charge–discharge performance (charging voltage of 1.71 V and discharge voltage of 1.26 V at 2 mA cm−2), large specific capacity (842 mAh gZn−1 at 5 mA cm−2), and excellent cycling stability (480 h). Interestingly, the (Ni,Co)S2-based Zn–air battery can efficiently power an electrochemical water-splitting unit with (Ni,Co)S2 serving as both the electrodes. This reveals that the prepared (Ni,Co)S2 has promising applications in future energy conversion and energy storage devices

In situ preparation, characterization, magnetic and catalytic studies of surfactant free RGO/FeₓCo₁₀₀₋ₓ nanocomposites

A novel, "wet" and "clean" methodology was developed to prepare FeₓCo₁₀₀₋ₓ nanoparticles on reduced graphene oxide (RGO) surfaces in an aqueous solution through a coreduction process. Without any surface treatment, FeₓCo₁₀₀₋ₓ nanoparticles can in situ grow on the RGO sheets. It was found that RGO nanosheets can effectively prevent the aggregation of FeₓCo₁₀₀₋ₓ nanoparticles. The results reveal that the RGO/FeₓCo₁₀₀₋ₓ nanocomposites have ferromagnetic characteristics and show composition dependent magnetic properties. The effectiveness of the as-prepared RGO/FeₓCo₁₀₀₋ₓ nanocomposites as solid phase heterogeneous catalysts have been evaluated, for the first time, on the well-known 4-nitrophenol (4-NP) reduction to 4-aminophenol (4-AP) in the presence of excess sodium borohydride. The effect of initial 4-NP concentration, and catalyst loading dose were evaluated. The catalyst efficiency was examined on the basis of turnover frequency (TOF) and recyclability. The RGO/Fe₂₅Co₇₅ nanocomposites exhibit good catalytic activity toward 4-nitrophenol (4-NP) reduction and the graphene oxide (GO) supports also enhance the catalytic activity via a synergistic effect. The as-prepared RGO/FeₓCo₁₀₀₋ₓ nanocomposite catalysts are very efficient, stable, easy to prepare, eco-friendly, cost-effective, and have potential industrial applications7 page(s

High-Index Faceted Cufes\u3csub\u3e2\u3c/sub\u3e Nanosheets with Enhanced Behavior for Boosting Hydrogen Evolution Reaction

A rational design of highly active and robust catalysts based on earth-abundant elements for hydrogen evolution reaction (HER) is essential for future renewable energy applications. Herein, we report the synthesis of a new class of ultrathin metallic CuFeS2 nanosheets (NSs) with abundant exposed high-index {04} facets. They serve as a robust catalyst for the HER with a lower onset potential of 28.1 mV, an overpotential of only 88.7 mV (at j = 10 mA cm−2) and remarkable long-term stability in 0.5 M H2SO4, which make them the best system among all the reported non-noble metal catalysts. The theoretical calculations reveal that the mechanistic origin for such a high HER activity should be attributed to the excess S2− active sites on the exposed {04} high-index facets of CuFeS2 NSs, which have a rather favorable Gibbs free energy for atomic hydrogen adsorption. The present work highlights the importance of designing ultrathin metallic chalcopyrite nanosheets with high-index facets in order to increase the number of active sites for boosting the HER performance

Nanocomposites CoPt-x/Diatomite-C as oxygen reversible electrocatalysts for zinc-air batteries: Diatomite boosted the catalytic activity and durability

The exploration of oxygen reversible electrocatalysts to boost oxygen reduction reaction and oxygen evolution reaction is critical for the development of high-performance aqueous Zn-air batteries. Since diatomite with porous structure can adsorb metal ions in aqueous solution, herein, we prepare the nanocomposite CoPt-x/Diatomite-C for both oxygen reduction and evolution reactions, and diatomite is found significantly promotes the electrocatalytic activity and durability. With the presence of diatomite, CoPt-1/Diatomite-C shows a lower Tafel slope (63 mV dec(-1) at high potential range), larger diffusion-limited current density (4.94 mA cm(-2)) and superior durability for ORR. Particularly, the specific and mass activities of CoPt-1/Diatomite-C for ORR are 0.74 mA cm(-2) and 286 mA mg(-1), respectively, which are 2.5 and 3.0 times higher than that of CoPt-1/C without diatomite; For OER, the overpotential of CoPt-9/Diatomite-C decreases nearly 30 mV at 10 mA cm(-2), while the Tafel slope also reduces 16 mV dec(-1) versus CoPt-9/C catalyst. Moreover, a rechargeable Zn-air battery with these composites as air-cathode is self-assembled, and diatomite boosts the battery performance with desirable properties. CoPt-9/Diatomite-C displays the optimal performance, with a power density of 140 mW cm(-2), a specific capacity of 616 mA h g(-1) at 10 mA cm(-2) and an exceedingly robust cycling life. This work provides a viable and cost-effective strategy for fabricating oxygen reversible electrocatalysts for metal-air battery applications. (C) 2018 Elsevier Ltd. All rights reserved

High-Index Faceted Cufes\u3csub\u3e2\u3c/sub\u3e Nanosheets with Enhanced Behavior for Boosting Hydrogen Evolution Reaction

A rational design of highly active and robust catalysts based on earth-abundant elements for hydrogen evolution reaction (HER) is essential for future renewable energy applications. Herein, we report the synthesis of a new class of ultrathin metallic CuFeS2 nanosheets (NSs) with abundant exposed high-index {04} facets. They serve as a robust catalyst for the HER with a lower onset potential of 28.1 mV, an overpotential of only 88.7 mV (at j = 10 mA cm−2) and remarkable long-term stability in 0.5 M H2SO4, which make them the best system among all the reported non-noble metal catalysts. The theoretical calculations reveal that the mechanistic origin for such a high HER activity should be attributed to the excess S2− active sites on the exposed {04} high-index facets of CuFeS2 NSs, which have a rather favorable Gibbs free energy for atomic hydrogen adsorption. The present work highlights the importance of designing ultrathin metallic chalcopyrite nanosheets with high-index facets in order to increase the number of active sites for boosting the HER performance

The built-in electric field across FeN/Fe3N interface for efficient electrochemical reduction of CO2 to CO

Understanding and controlling chemical environment of metal-N-catalysts is of great importance. In this work, the authors reveal FeN/Fe3N interface with Fe-N4 and Fe-N2 coordination sites for enhanced electrochemical CO2 reduction to CO