Facile generation of CeO2 nanoparticles on multiphased NiSx nanoplatelet arrays as a free-standing electrode for efficient overall water splitting

Constructing nanostructured electrocatalysts with heterointerface and finetuning their electronic properties are essential for high-efficient overall water splitting. Here, we prepared a well-designed nano-flower-like multiphase and hybrid material of NiS/NiS2/CeO2/NF (NiSx/CeO2/NF) with rich heterointerfaces and abundant active sites through solvothermal reaction and post-annealing treatment. The as-fabricated NiSx/CeO2/NF exhibits exceptional catalytic performance for OER and HER. Specifically, in 1 M KOH solution, it requires the low overpotentials of 326 and 92 mV to achieve the current density of 200 and 10 mA cm-2 for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER), respectively. More satisfactorily, when NiSx/CeO2/NF is used as the bifunctional catalyst, a low voltage of only 1.53 V is required to achieve a current density of 10 mA cm-2 for overall water splitting. The excellent catalytic performance should be attributed to its special heterogeneous structure and the synergy effect between NiSx and CeO2. This work emphasizes the important significance of constructing efficient bifunctional electrocatalysts by reasonably designing heterostructures and multiphase components for overall water splitting.

Recent Progress on Phase Engineering of Nanomaterials

As a key structural parameter, phase depicts the arrangement of atoms in materials. Normally, a nanomaterial exists in its thermodynamically stable crystal phase. With the development of nanotechnology, nanomaterials with unconventional crystal phases, which rarely exist in their bulk counterparts, or amorphous phase have been prepared using carefully controlled reaction conditions. Together these methods are beginning to enable phase engineering of nanomaterials (PEN), i.e., the synthesis of nanomaterials with unconventional phases and the transformation between different phases, to obtain desired properties and functions. This Review summarizes the research progress in the field of PEN. First, we present representative strategies for the direct synthesis of unconventional phases and modulation of phase transformation in diverse kinds of nanomaterials. We cover the synthesis of nanomaterials ranging from metal nanostructures such as Au, Ag, Cu, Pd, and Ru, and their alloys; metal oxides, borides, and carbides; to transition metal dichalcogenides (TMDs) and 2D layered materials. We review synthesis and growth methods ranging from wet-chemical reduction and seed-mediated epitaxial growth to chemical vapor deposition (CVD), high pressure phase transformation, and electron and ion-beam irradiation. After that, we summarize the significant influence of phase on the various properties of unconventional-phase nanomaterials. We also discuss the potential applications of the developed unconventional-phase nanomaterials in different areas including catalysis, electrochemical energy storage (batteries and supercapacitors), solar cells, optoelectronics, and sensing. Finally, we discuss existing challenges and future research directions in PEN.

d-sp orbital hybridization: a strategy for activity improvement of transition metal catalysts

Orbital hybridization to regulate the electronic structures and surface chemisorption properties of transition metals has been extensively investigated for searching high-performance catalysts toward various reactions. Unlike conventional d-d hybridization, the d-sp hybridization interaction between transition metals and p-block elements could result in surprising electronic properties and catalytic activities. This feature article highlights the recent progress in the development of high-performance transition metal-based catalysts through the extraordinary d-sp hybridization strategy, particularly for energy-related electrocatalytic applications. We start by giving an introduction of fundamental concepts associated with electronic structures of transition metal catalysts, including the Sabatier principle, d-band theory, electronic descriptor, as well as the comparison of d-d hybridization and d-sp hybridization strategies. Then, we summarize the theoretical and experimental advances in d-sp hybridization catalysts, including p-block element-doped metal catalysts, intermetallic catalysts and supported metal catalysts, with emphasis on the important roles of d-sp hybridization in tuning catalytic performances. Finally, we present existing challenges and future development prospects for the rational design of advanced d-sp hybridization catalysts.