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Co 3 O 4 nanoparticles with Ag single atoms tetrahedrally doped in the lattice are fabricated on the surface of carbon nanotubes (Ag-Co 3 O 4 /CNT) through pyrolysis of the AgCo precursor/CNT aerogel. The unique architecture modifies the electron properties of Co and Ag, which expedites the charge transfer and promotes *OOH desorption during OER. Consequently, Ag-Co 3 O 4 /CNT exhibits optimized intrinsic activity and OER kinetics. [Display omitted] • Ag-Co 3 O 4 /CNT that Ag single atom embedded in Co 3 O 4 nanoparticles on the surface of CNT was developed as OER electrocatalyst. • The lattice doping generates electronic interaction between Ag and host Co 3 O 4 , cutting down the charge transfer resistance. • The tetrahedral doping Ag atom effectively accelerates the desorption process and optimizes the intrinsic activity for OER. • The unique doping structure is also conducive to the structure and activity stability. Incorporating noble metal single atoms into lattice of spinel cobalt oxide (Co 3 O 4) is an attractive way to fabricate oxygen evolution reaction (OER) electrocatalysts because of the high activity and economic benefit. The commonly used high valence noble metal dopants such as ruthenium, iridium and rhodium tend to supersede Co3+ at octahedral site of Co 3 O 4 and result in great activity, the origins of admirable activity were also wildly investigated. However, bare explorations on doping noble metal single atom into tetrahedral site of Co 3 O 4 to construct OER catalyst have been reported, corresponding catalytic activity and mechanism remain mystery. Here, a promising structure that tetrahedrally substituent Ag single atom embedded in Co 3 O 4 nanoparticles on the surface of carbon nanotube (Ag-Co 3 O 4 /CNT) was presented, and its performance in OER was probed. The high angle annular dark field-scanning transmission electron microscopy (HAADF-STEM) and X-ray absorption spectroscopy (XAS) demonstrate the successful embeddedness of atomical Ag atom in Co 3 O 4 lattice, the resultant electronic interaction is conducive to promote charge transfer for OER. Theoretical calculations further disclose that atomical Ag dopant prefers to replace tetrahedral Co2+ rather than octahedral Co3+. The substitution Ag acts as the active site through Ag-Co bridge and facilitates the desorption process, which improves the turnover frequency (TOF) and boosts the intrinsic activity of Ag-Co 3 O 4 /CNT. Benefiting from the essentials above, Ag-Co 3 O 4 /CNT displays remarkable activity (236 mV@10 mA cm−2) and robust stability for alkaline OER. This finding offers a potential direction for the design of noble metal single atom involved Co 3 O 4 based OER electrocatalysts. [ABSTRACT FROM AUTHOR]

The synthesized Ag@CoMo-LDH electrode exhibited distinguished electrocatalytic performance compared with most reported advanced OER electrocatalysts. [Display omitted] Modulating electronic resistance properties and enhancing both active site populations and per-site activity are highly desirable for the application of layered double hydroxides (LDHs) in the electrocatalytic oxygen evolution reaction (OER). Herein, a metal-support structure consisting of silver (Ag) nanoparticles supported by MoO 4 2− intercalated Co-LDH (CoMo-LDH) nanocages (Ag@CoMo-LDH) was developed using a sacrificial template method and a subsequent spontaneous strategy. The resultant hybrid was shown to be a highly efficient OER electrocatalyst in alkaline media. The required overpotential of Ag@CoMo-LDH for affording a geometric current density of 10 mA cm−2 is as low as 205 mV, which is not only significantly lower than that of separate CoMo-LDH or Ag nanoparticles but also superior to that of most developed OER electrocatalysts reported recently. The constituents and respective work mechanism of Ag@CoMo-LDH are discussed in detail. The superior performance of Ag@CoMo-LDH is related to the unique construction and the effective and stable heterointerfaces between Ag nanoparticles and CoMo-LDH, which accelerate the electron and mass transfer, provide a large number of new active sites and optimize the activity of the original sites. Impressively, Ag@CoMo-LDH also exhibited promising practical prospect on account of the remarkable cyclic and long-term stability. This finding demonstrates that pointedly integrating multiple strategies into one system is a promising way to construct new LDH-based OER electrocatalysts with synthetically improved performance, providing a promising model for developing advanced electrocatalysts in energy conversion devices. [ABSTRACT FROM AUTHOR]

The synthesized Ag@Co-LDH electrode exhibited distinguished electrocatalytic performance compared with most reported advanced OER electrocatalysts. [Display omitted] • Heterostructure electrocatalyst that Ag nanowires shelled with Co-LDH nanosheets (Ag@Co-LDH) was constructed. • Ag nanowires and heterointerfaces offer a high-efficiency electron transportation during OER. • Co-LDH with ultrathin sheet-like structure and abundant grain boundary defects provide plenty of active sites for OER. • Electronic interaction and plentiful amorphous regions enhance the intrinsic activity of active site. • Ag@Co-LDH exhibits remarkable OER activity and superior electrochemical stability. It is highly desirable to cut down the electron transfer resistance, improve both site activity and site populations of layered double hydroxides (LDHs) for enhanced electrochemical activity of oxygen evolution reaction (OER). Herein, the hybrid that Co-LDH nanosheets shells grown on Ag nanowires (NWs) cores (Ag@Co-LDH) was constructed and applied as a favorable OER electrocatalyst. The high conductivity of Ag NWs and heterointerface between Ag NWs and Co-LDH gravely accelerate electron transfer. Co-LDH with ultrathin sheet-like structure and abundant grain boundary defects effectively provide lots of active sites. The optimized local environment of Co atoms by Ag dopants and plentiful amorphous regions strongly enhance the intrinsic activity of active site. Therefore, the as-prepared Ag@Co-LDH demonstrates distinguished OER activity with a low overpotential of 217 mV at the current density of 10 mA cm−2, which is superior to most reported advanced OER electrocatalysts and even commercial Ir/C. Moreover, benefiting from the unique structure and stable heterointerface, Ag@Co-LDH also exhibits robust cycling stability and long-term durability proved by accelerated degradation test (ADT) and galvanostatic test, respectively. This finding provides a practical design direction for high-performance LDH-based OER electrocatalysts. [ABSTRACT FROM AUTHOR]

A self-supporting binder-free electrocatalyst named Ni-ANS@NiFe 2 O 4 /IF-3 was successfully synthesized by two-step hydrothermal method, which possess an unique nanoflower structure and excellent OER performance and durability under alkaline conditions. [Display omitted] • The Ni-ANS@NiFe 2 O 4 /IF-3 was synthesized through a simple two-step hydrothermal method. • Nanoflower structure was formed by uniformly covering spinel NiFe 2 O 4 with amorphous Ni nanosheets. • The evolution process of nanoflower structure and its effect on catalytic activity were revealed. • The prepared catalyst showed extraordinary OER activity and stability under alkaline conditions. As a bottleneck step in electrochemical water splitting, oxygen evolution reaction (OER) seriously limits the development of large-scale electrochemical hydrogen production. Rational design and development of an efficient and stable OER electrocatalysts are of enormous importance but still challenging for electrochemical energy conversion. In this work, a unique nanoflower like electrocatalyst consisting of NiFe 2 O 4 nanoparticles wrapped with amorphous Ni based nanosheet on the 3D porous iron foam (IF) substrate (named as Ni-ANS@NiFe 2 O 4 /IF) is proposed and the evolution of catalyst morphology and its effect on electrochemical activity were explored. Profiting from the unique nanoflower structure and the coupling of ample active substances with favorable conductive substrates, the prepared Ni-ANS@NiFe 2 O 4 /IF exhibits outstanding OER activity with low overpotential of 209, 251, 270 mV to reach a current density of 10, 100 and 200 mA cm−2, and admirable long-term stability. This work may broaden a new vision and avenue for the design of efficient OER catalysts. [ABSTRACT FROM AUTHOR]

• The Ni 0.85 Se-O/CN catalyst is multicore core–shell heterojunction microspheres. • The core–shell heterojunction structure enhances electron transport. • Ni 0.85 Se-O/CN is protected by g-C 3 N 4 , which reduces the corrosion and oxidation. • Core-shell engineering enhanced the OER catalytic activity of Ni 0.85 Se-O/CN. Efficient electrocatalysts are of great consideration for lowering the potential barrier for the oxygen evolution reaction (OER). The Ni 0.85 Se-O/CN multicore core–shell coated structured microspherical electrocatalyst was prepared by a simple hydrothermal method for promoting OER in alkaline solution. With highly conductive Ni 0.85 Se-O as the core and g-C 3 N 4 with abundant active sites as the shell, the electrocatalyst exhibits excellent catalytic OER performance with a Tafel slope of 82.5 mV dec−1 and an overpotential of 240 mV @ 10 mA cm−2. What's more, the catalyst exhibits excellent long-term stability, which is facilitated by the protection of the core (Ni 0.85 Se-O) from corrosion and oxidation by the shell (g-C 3 N 4). In addition, in-depth mechanistic analysis on catalytic activity of materials were performed by density functional theory (DFT). This work highlights the importance of core–shell structural engineering to improve the catalytic activity of materials and provides new possibilities for the progress of Ni-based catalysts in the field of oxygen evolution reaction. [ABSTRACT FROM AUTHOR]

The obtained NiFe-LDH@Fe-MOF/IF-2 electrode with unique hierarchical structure exhibited distinguished electrocatalytic performance and extraordinary durability OER in alkaline conditions. [Display omitted] • The NiFe-LDH@Fe-MOF/IF-2 was synthesized through a simple two-step hydrothermal method. • NiFe-LDH@Fe-MOF/IF-2 characterized excellent OER activity in alkaline conditions. • NiFe-LDH@Fe-MOF/IF-2 in-situ growth on the surface of IF improves conductivity and stability. • In situ partial transformation of amorphous NiFe-LDH greatly improves the OER performance. Metal-organic frameworks (MOFs) have been extensively researched in recent years benefiting from the large surface area, abundant active centers, and adjustable structure. However, low conductivity and inaccessible active sites severely hinder its application in water electrolysis. Herein, a self-supporting electrocatalyst by developing MOF derivative on the surface of iron foam (IF) was synthesized through a self-templated partial transformation strategy. In addition, a series of catalysts with different morphologies were synthesized by adjusting the amount of Ni and the reaction time. Profiting from the unique hierarchical structure with large active area and abundant active sites, strong combination of highly active amorphous NiFe-LDH and Fe-MOF, and high conductivity and stability of the MOFs array in situ growth on IF, the resulting NiFe-LDH@Fe-MOF/IF-2 shows excellent oxygen evolution reaction (OER) activity in alkaline electrolyte with required overpotentials of 183, 237 and 257 mV to achieve current densities of 10, 100, and 200 mA cm−2, respectively, and long-term stability for at least 20 h. This work provides new insights for the design and development of self-supporting MOFs derived high performance electrocatalysts. [ABSTRACT FROM AUTHOR]