Xinghua Han

Bio: Xinghua Han is an academic researcher from North University of China. The author has contributed to research in topics: Overpotential & Water splitting. The author has co-authored 4 publications.

Promoting urea oxidation and water oxidation through interface construction on a CeO2@CoFe2O4 heterostructure.

Abstract: Spinel ferrites are considered practical and promising oxygen evolution reaction (OER) and urea oxidation reaction (UOR) electrocatalysts because of their advantages in the adsorption and activation of electrocatalytic substances. A CeO2 functional metal oxide was used to modify a spinel oxide in order to further improve the electrocatalytic performance of the spinel oxide. In this work, a CeO2@CoFe2O4/NF hybrid nanostructure was synthesized for the first time by typical hydrothermal and calcination methods. In an alkaline medium, CeO2@CoFe2O4/NF displays superior OER activity and needs an overpotential of 213 mV to deliver a current density of 100 mA cm−2, which makes it one of the most active catalysts reported so far. In addition, the as-prepared CeO2@CoFe2O4/NF material needs a potential of 1.40 V at the same current density in 1.0 M KOH with 0.5 M urea, which displays superior UOR activity. The CeO2@CoFe2O4/NF catalyst also displays good durability and the performance of the electrode is negligibly attenuated at a large current intensity of 125 mA cm−2. Experimental results demonstrate that the activity of the CeO2@CoFe2O4/NF catalyst is ascribed to the exposure of more active centers and a faster electron transfer rate. This work develops a novel method for exploiting Earth-abundant, robust and environmentally friendly OER and UOR electrocatalysts.

Controllable synthesis of Ni3S2@MOOH/NF (M = Fe, Ni, Cu, Mn and Co) hybrid structure for the efficient hydrogen evolution reaction

Abstract: The design and synthesis of hybrid core–shell catalysts is of great significance for obtaining an excellent performance of hydrogen evolution reaction (HER). However, it remains a challenge to explore the exact active sites and research the catalytic mechanism for HER. Here, a series of Ni3S2@MOOH/NF (M = Fe, Ni, Cu, Mn and Co) hybrid structures is firstly in-site grown on Ni foam by the typical hydrothermal and electrodeposition methods. The Ni3S2@NiOOH/NF catalyst with a core–shell structure exhibits a relatively low overpotential of 79 mV for HER at a current density of 10 mA cm−2, which is one of the best catalytic activities reported so far. Moreover, it also shows good stability in the long-term durability test. Various spectral analysis and density functional theory calculations demonstrate that NiOOH is favorable for the adsorption of water molecules, and the S atom at the interface between Ni3S2 and NiOOH is favorable for the adsorption of H intermediates, which strongly accelerates the HER process in alkaline solution. This work provides a general strategy for the synthesis of electrocatalytic materials, which can be used for efficient electrocatalytic water splitting reactions.

Controlled synthesis of P-Co3O4@NiCo-LDH/NF nanoarrays as binder-free electrodes for water splitting.

Abstract: The design and development of robust and environmentally friendly electrocatalytic materials are of great significance to the hydrogen production industry for the electrolysis of water. A series of P-Co3O4@NiCo-LDH/NF materials was firstly successfully synthesized by a hydrothermal method, high temperature calcination and an electrochemical deposition approach when sodium hypophosphite was used as the source of P and Ni(NO3)2·6H2O as the source of nickel and introduced cobalt at the same time. The structure, composition, morphology and electrochemical performance of the P-Co3O4@NiCo-LDH/NF electrocatalytic material were determined by X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy and electrochemical performance testing. It is worth noting that the P-Co3O4@NiCo-LDH-2/NF material presents excellent hydrogen evolution reaction performance in 1 M KOH alkaline solution. It only needs an overpotential of 181 mV to drive a current density of 100 mA cm−2, which is one of the best catalytic activities reported so far. The experimental results and theoretical calculations demonstrate that the electrocatalytic activity of the P-Co3O4@NiCo-LDH-2/NF material is attributed to the faster electron transfer rate, exposure of more active sites, optimal water adsorption energy and better electrical conductivity.

Water electrolysis: from textbook knowledge to the latest scientific strategies and industrial developments

Abstract: Replacing fossil fuels with energy sources and carriers that are sustainable, environmentally benign, and affordable is amongst the most pressing challenges for future socio-economic development. To that goal, hydrogen is presumed to be the most promising energy carrier. Electrocatalytic water splitting, if driven by green electricity, would provide hydrogen with minimal CO2 footprint. The viability of water electrolysis still hinges on the availability of durable earth-abundant electrocatalyst materials and the overall process efficiency. This review spans from the fundamentals of electrocatalytically initiated water splitting to the very latest scientific findings from university and institutional research, also covering specifications and special features of the current industrial processes and those processes currently being tested in large-scale applications. Recently developed strategies are described for the optimisation and discovery of active and durable materials for electrodes that ever-increasingly harness first-principles calculations and machine learning. In addition, a technoeconomic analysis of water electrolysis is included that allows an assessment of the extent to which a large-scale implementation of water splitting can help to combat climate change. This review article is intended to cross-pollinate and strengthen efforts from fundamental understanding to technical implementation and to improve the ‘junctions’ between the field's physical chemists, materials scientists and engineers, as well as stimulate much-needed exchange among these groups on challenges encountered in the different domains.

Bimetallic Multi-Level Layered Co-NiOOH/Ni3 S2 @NF Nanosheet for Hydrogen Evolution Reaction in Alkaline Medium.

Abstract: Development of efficient non-noble metal catalysts for water splitting is of great significance but challenging due to the sluggish kinetics of the hydrogen evolution reaction (HER) in alkaline medium. Herein, a bimetallic multi-level layered catalytic electrode composed of Ni3 S2 nanosheets with secondary Co-NiOOH layer of 3D porous and free-standing cathode in alkaline medium is reported. This integrated synergistic catalytic electrode exhibits excellent HER electrocatalytic performance. The resultant Ni0.67 Co0.33 /Ni3 S2 @NF electrode displays the highest HER activity with only overpotentials of 87 and 203 mV to afford current densities of 10 and 100 mA·cm-2 , respectively, and its Tafel slope is 80 mV·dec-1 . The chronopotentiometry operated at high current density of 50 mA·cm-2 shows negligible deterioration, indicating better stability of Ni0.67 Co0.33 /Ni3 S2 @NF electrode than Pt/C (20 wt.%). Such a desirable catalytic performance is attributed to the modification of physical and electronic structure that exposes abundant active sites and improves the intrinsic catalytic activity toward HER, which is also confirmed by electrochemically active surface area and X-ray photoelectron spectroscopy analysis. This work provides a strong support for the rational design of high-performance bimetallic electrodes for industrial water splitting.

Synergistic effect of the MoO2/CeO2 S-scheme heterojunction on carbon rods for enhanced photocatalytic hydrogen evolution.

Abstract: The separation efficiency of photogenerated carriers is a key factor affecting photocatalytic hydrogen evolution activity. However, loading precious metals is a cost problem, so in this work cheap carbon rods are introduced into the S-scheme heterojunction of CeO2/MoO2 as electron transfer channels. The construction of the S-scheme heterojunction greatly improves the reduction activity of a single catalyst and effectively inhibits the recombination of photogenerated electrons and holes. The carbon rods at the interface between CeO2 and MoO2 can ensure the rapid transfer of space charge, thus significantly improving the separation efficiency of photogenerated carriers. The synergistic effect of these two promotes the composite catalyst's photocatalytic hydrogen evolution activity. After optimization, the photocatalytic hydrogen evolution amount of 30% CeO2/MoO2-C (6725 μmol g-1) is 18.6 and 2.43 times those of CeO2 (373 μmol g-1) and MoO2-C (2771 μmol g-1), respectively. 30% CeO2/MoO2-C showed good stability in the photocatalytic cycle experiment. Simultaneously, steady-state fluorescence and electrochemical characterization showed that the introduction of carbon rods promoted the spatial transfer of electrons. This work provides a new design idea and method for applying and developing the S-scheme heterojunction.