Heteroatom Ni alloyed pyrite-phase FeS2 as a pre-catalyst for enhanced oxygen evolution reaction

Developing Superior Hydrophobic 3D Hierarchical Electrocatalysts Embedding Abundant Catalytic Species for High Power Density Zn-Air Battery

It is essential but still challenging to design and construct inexpensive, highly active bifunctional oxygen electrocatalysts for the development of high power density zinc-air batteries (ZABs). Herein, a CoFe-S@3D-S-NCNT electrocatalyst with a 3D hierarchical structure of carbon nanotubes growing on leaf-like carbon microplates is designed and prepared through chemical vapour deposition pyrolysis of CoFe-MOF and subsequent hydrothermal sulfurization. Its 3D hierarchical structure shows excellent hydrophobicity, which facilitates the diffusion of oxygen and thus accelerates the oxygen reduction reaction (ORR) kinetic process. Alloying and sulfurization strategies obviously enrich the catalytic species in the catalyst, including cobalt or cobalt ferroalloy sulfides, their heterojunction, core-shell structure, and S, N-doped carbon, which simultaneously improve the ORR/OER catalytic activity with a small potential gap (ΔE = 0.71 V). Benefiting from these characteristics, the corresponding liquid ZABs show high peak power density (223 mW cm^-2 ), superior specific capacity (815 mA h g_Zn ^-1 ), and excellent stability at 5 mA cm^-2 for ≈900 h. The quasi-solid-state ZABs also exhibit a very high peak power density of 490 mW cm^-2 and an excellent voltage round-trip efficiency of more than 64%. This work highlights that simultaneous composition optimization and microstructure design of catalysts can effectively improve the performance of ZABs.

Skeleton-coated CoCu-Based bimetal hollow nanoprisms as High-Performance electrocatalysts for oxygen evolution reaction

CoSx materials with high catalytic activity are considered as promising HER electrocatalysts, but their inherent low electrical conductivity and easy loss of active sites have greatly limited their applications in OER electrocatalysis. Herein, we present a convenient method to synthesize Co-Cu hollow nanoprisms after wrapping and calcining with trithiocyanuric acid (C3H3N3S3) (denoted N-Co-Cu-S-x HNs). The results showed that Cu doping modified the charge density of Co center, leading to the enhancement of the intrinsic activity of the Co3S4 active center, meanwhile wrapping trithiocyanuric acid on the surfaces and calcinating to form N-containing C skeleton as a flexible substrate to encapsulate the catalysts, which effectively protected the active sites inside the catalysts. Notably, the OER catalyst that was optimized by adjusting the metal ratio and controlling the trithiocyanuric acid incorporation exhibited a low overpotential of 306 mV under a current density of 10 mA cm-2 and showed a superior durability of more than 27 h. This work may provide some insights into the preparation of oxygen evolution reaction catalysts with excellent performance through doping transition metals and protecting the internal active sites strategies.

Internal electric field induced photocarriers separation of nickel-doped pyrite/pyrite homojunction with rich sulfur vacancies for superior Cr(VI) reduction

Improving the separation efficiency and transfer ability of photoinduced electrons/holes in pyrite (FeS2)-based photocatalytic materials is significant for the photoreduction of hexavalent chromium (Cr(VI)) but still remains a challenge. Herein, a novel homojunction was prepared through in-situ growth of nickel (Ni) doped FeS2 nanoparticles on FeS2 nanobelts (denoted as Ni-FeS2/FeS2). Systematical characterizations revealed that Ni doped FeS2 nanoparticles have been successfully in situ grown along the lattice of FeS2 nanobelts. Photoreduction experiments demonstrated that the Ni-FeS2/FeS2 homojunction with 2 mmol Ni doping contents (denoted as 2Ni-FeS2/FeS2) exhibited the optimum Cr(VI) reduction efficiency among the studied catalysts. Density Functional Theory (DFT) calculated results verified that Ni doping could not only be advantageous for the formation of sulfur vacancies but also modify the band gap and band structure of FeS2 nanoparticles. Moreover, several doping energy levels caused by Ni doping have also appeared near the Fermi level of FeS2 nanoparticles. The migration paths of electrons and the existence of internal electric field (IEF) in homojunction were further verified by the calculation of work function. To sum up, the doping energy levels and IEF that produced by homojunction played important roles in accelerating the separation efficiency of its photogenerated carriers.

Low-dimensional transition metal sulfide-based electrocatalysts for water electrolysis: overview and perspectives

Hydrogen prepared by electrocatalytic decomposition of water ("green hydrogen") has the advantages of high energy density and being clean and pollution-free, which is an important energy carrier to face the problems of the energy crisis and environmental pollution. However, the most used commercial electrocatalysts are based on expensive and scarce precious metals and their alloy materials, which seriously restricts the large-scale industrial application of hydrogen energy. The development of efficient non-precious metal electrocatalysts is the key to achieving the sustainable development of the hydrogen energy industry. Transition metal sulfides (TMS) have become popular non-precious metal electrocatalysts with great application potential due to their large specific surface area, unique electronic structure, and rich regulatory strategies. To further improve their catalytic activities for practical application, many methods have been tried in recent years, including control of morphology and crystal plane, metal/nonmetal doping, vacancy engineering, building of self-supporting electrocatalysts, interface engineering, etc. In this review, we introduce firstly the common types of TMS and their preparation. Additionally, we summarize the recent developments of the many different strategies mentioned above for efficient water electrolysis applications. Furthermore, the rationales behind their enhanced electrochemical performances are discussed. Lastly, the challenges and future perspectives are briefly discussed for TMS-based water dissociation catalysts.

Electrochemical incorporation of heteroatom into surface reconstruction induced Ni vacancy of NixO nanosheet for enhanced water oxidation

Surface reconstruction of non-oxide oxygen evolution reaction (OER) electrocatalysts has been intensively studied to improve their catalytic performances. However, further modification of the reconstructed active surfaces for better catalytic performances has not been reported. In this work, NiSe nanorods are prepared on nickel foam (NiSe@NF) as the pre-catalyst for electrochemical OER. It is revealed that non-stoichiometric NiO nanosheets with abundant Ni vacancies (Ni_xO) are formed on the surfaces of NiSe nanorods (Ni_xO/NiSe@NF) via in-situ electrochemical oxidation. Furthermore, the OER performances are obviously improved after heteroatom Fe is incorporated electrochemically into Ni_xO nanosheets ((FeNi)O/NiSe@NF). For OER to have a current density of 20 mA cm^-2 in 1 M KOH solution, the as-prepared (FeNi)O/NiSe@NF electrode only needs an overpotential of 268 mV. Density functional theory (DFT) calculations reveal that the formation of Ni vacancy can increase the free energy of *OH. More importantly, the incorporation of heteroatom Fe into Ni vacancy can significantly decrease the free energy of *O, which enables Fe-NiO to have the lowest theoretical overpotential for OER in this work. The present work provides a facile and universal strategy to modify the reconstructed active oxides' surfaces for higher electrocatalytic performances.

Electrochemically reconstructed high-entropy amorphous FeCoNiCrVB as a highly active oxygen evolution catalyst

Highly active and robust electrocatalysts for the oxygen evolution reaction by intentional surface reconstruction of high-entropy amorphous alloys.