Balancing Activity and Stability in Spinel Cobalt Oxides through Geometrical Sites Occupation towards Efficient Electrocatalytic Oxygen Evolution

Designing active and stable oxygen evolution reaction (OER) catalysts are vitally important to various energy conversion devices. Herein, we introduce elements Ni and Mn into (Co)_tet(Co₂)_octO₄ nanosheets (NSs) at fixed geometrical sites, including Mn_oct, Ni_oct, and Ni_tet, to optimize the initial geometrical structure and modulate the CoCo₂O₄ surface from oxygen-excess to oxygen-deficiency. The pristine (Ni,Mn)-(Co)_tet(Co₂)_octO₄ NSs shows excellent OER activity with an overpotential of 281.6 mV at a current density of 10 mA cm⁻². Moreover, without damaging their initial activity, the activated (Act)-(Ni,Mn)-(Co)_tet(Co₂)_octO₄ NSs after surface reconstruction exhibit long-term stability of 100 h under 10 mA cm⁻², 50 mA cm⁻², or even 100 mA cm⁻². The optimal balance between electroactivity and stability leads to remarkable OER performances, providing a pivotal guideline for designing ideal electrocatalysts and inspiring more works to focus on the dynamic change of each occupation site component.     

Revealing the Formation Mechanism and Optimizing the Synthesis Conditions of Layered Double Hydroxides for the Oxygen Evolution Reaction

Layered double hydroxides (LDHs), whose formation is strongly related to OH⁻ concentration, have attracted significant interest in various fields. However, the effect of the real-time change of OH⁻ concentration on LDHs’ formation has not been fully explored due to the unsuitability of the existing synthesis methods for in situ characterization. Here, the deliberately designed combination of NH₃ gas diffusion and in situ pH measurement provides a solution to the above problem. The obtained results revealed the formation mechanism and also guided us to synthesize a library of LDHs with the desired attributes in water at room temperature without using any additives. After evaluating their oxygen evolution reaction performance, we found that FeNi-LDH with a Fe/Ni ratio of 25/75 exhibits one of the best performances so far reported.     

Hierarchical Hollow Nanoprisms Based on Ultrathin Ni‐Fe Layered Double Hydroxide Nanosheets with Enhanced Electrocatalytic Activity towards Oxygen Evolution

The oxygen evolution reaction (OER) is involved in various renewable energy systems, such as water‐splitting cells and metal–air batteries. Ni‐Fe layered double hydroxides (LDHs) have been reported as promising OER electrocatalysts in alkaline electrolytes. The rational design of advanced nanostructures for Ni‐Fe LDHs is highly desirable to optimize their electrocatalytic performance. Herein, we report a facile self‐templated strategy for the synthesis of novel hierarchical hollow nanoprisms composed of ultrathin Ni‐Fe LDH nanosheets. Tetragonal nanoprisms of nickel precursors were first synthesized as the self‐sacrificing template. Afterwards, these Ni precursors were consumed during the hydrolysis of iron(II) sulfate for the simultaneous growth of a layer of Ni‐Fe LDH nanosheets on the surface. The resultant Ni‐Fe LDH hollow prisms with large surface areas manifest high electrocatalytic activity towards the OER with low overpotential, small Tafel slope, and remarkable stability.     

Stabilizing Low-Valence Single Atoms by Constructing Metalloid Tungsten Carbide Supports for Efficient Hydrogen Oxidation and Evolution

Designing novel single-atom catalysts (SACs) supports to modulate the electronic structure is crucial to optimize the catalytic activity, but rather challenging. Herein, a general strategy is proposed to utilize the metalloid properties of supports to trap and stabilize single-atoms with low-valence states. A series of single-atoms supported on the surface of tungsten carbide (M-WC_x, M=Ru, Ir, Pd) are rationally developed through a facile pyrolysis method. Benefiting from the metalloid properties of WC_x, the single-atoms exhibit weak coordination with surface W and C atoms, resulting in the formation of low-valence active centers similar to metals. The unique metal-metal interaction effectively stabilizes the low-valence single atoms on the WC_x surface and improves the electronic orbital energy level distribution of the active sites. As expected, the representative Ru-WC_x exhibits superior mass activities of 7.84 and 62.52 A mg_Ru⁻¹ for the hydrogen oxidation and evolution reactions (HOR/HER), respectively. In-depth mechanistic analysis demonstrates that an ideal dual-sites cooperative mechanism achieves a suitable adsorption balance of H_ad and OH_ad, resulting in an energetically favorable Volmer step. This work offers new guidance for the precise construction of highly active SACs.     

Boosting the Activity of Pd Single Atoms by Tuning Their Local Environment on Ceria for Methane Combustion

Supported Pd single atom catalysts (SACs) have triggered great research interest in methane combustion yet with contradicting views on their activity and stability. Here, we show that the Pd SAs can take different electronic structure and atomic geometry on ceria support, resulting in different catalytic properties. By a simple thermal pretreatment to ceria prior to Pd deposition, a unique anchoring site is created. The Pd SA, taking this site, can be activated to Pd^δ+ (0<δ<2) that has greatly enhanced activity for methane oxidation: T₅₀ lowered by up to 130 °C and almost 10 times higher turnover frequency compared to the untreated catalyst. The enhanced activity of Pd^δ+ site is related to its oxygen-deficient local structure and elongated interacting distance with ceria, leading to enhanced capability in delivering reactive oxygen species and decomposing reaction intermediates. This work provides insights into designing highly efficient Pd SACs for oxidation reactions.     

Ni掺杂ZIF-65复合材料的制备及其电催化析氧性能

以ZIF-65作为前驱体,通过简单的化学沉淀法对其进行了镍的掺杂。X射线衍射仪和扫描电子显微镜表征结果显示成功合成了形貌均匀的Ni掺杂ZIF-65。我们检验了ZIF-65以及Ni掺杂ZIF-65在三电极体系中的电催化氧析出反应的活性。结果表明Ni的掺杂提高了ZIF-65的电催化活性,并优于传统贵金属催化剂二氧化钌的电催化性能。     

Oxygen Evolution and Reduction Reaction Activity Investigations on Fe,Co or Ni embedded Tetragonal Graphene by A Thermodynamical Full-Landscape Searching Scheme

Single transition metal (TM) atoms such as Fe, Co and Ni occupying a carbon divacancy in tetragonal graphene (TG) and bonded with four nitrogen atoms (TM@N₄TG) as electrocatalysts are investigated by means of first-principles calculations. To consider the effect of solvent species on the local configuration of the active single metal, a thermodynamical full-landscape searching (TFLS) scheme is employed. The calculated thermodynamic overpotentials (η_td) from our TFLS indicate that Co@N₄TG displays high catalytic activity toward both oxygen evolution reaction (OER) and reduction reaction (ORR), with η_td^OER and η_td^ORR as 0.397 and 0.357 V, respectively. Its OER potential cannot be captured if only one four electron reaction loop (FERL) is considered. The actual active pathways do not always turn out to be the reactions starting from the bare site. Our findings demonstrate that TG is a promising support and TM confined TD can be used to design effective and cheap multifunctional electrocatalysts.     

不同方法制备的CeO2载体对CuO/CeO2催化剂水煤气变换活性和稳定性的影响

分别采用沉淀法(A),水热法(B)和柠檬酸溶胶-凝胶法(C)制备了三种CeO2材料,并以其为载体采用沉积-沉淀法制备了CuO/CeO2催化剂.运用N2物理吸附、粉末X射线衍射(PXRD)、原位粉末X射线衍射(in situ PXRD)、氢气-程序升温还原(H2-TPR)和循环伏安法(CV)等技术对其进行了表征,考察了不同方法制备的CeO2载体对CuO/CeO2水煤气变换(WGS)催化剂的结构、氧化-还原性能、催化活性和稳定性的影响.结果表明,它们的催化活性和稳定性顺序都是CuO/CeO2-A＞CuO/CeO2-B＞CuO/CeO2-C.联系表征结果,CuO/CeO2催化剂的活性与催化剂中CuO的颗粒度、CuO的微观应力和中等大小且与二氧化铈相互作用的CuO的数量等有关,而这些因素很大程度上受CeO2载体本身的热稳定性的影响.根据CV中扫描次数的增加,Cu2+←→Cu0氧化还原峰面积减小,推断CuO/CeO2催化剂在一定条件下氧化还原是不可逆的,这可能是其在反应气氛下经受温度循环之后活性降低的原因.     

不同方法制备的CeO2载体对CuO/CeO2催化剂水煤气变换活性和稳定性的影响

分别采用沉淀法(A), 水热法(B)和柠檬酸溶胶-凝胶法(C)制备了三种CeO2材料, 并以其为载体采用沉积-沉淀法制备了CuO/CeO2催化剂. 运用N2物理吸附、粉末X射线衍射(PXRD)、原位粉末X射线衍射(in situ PXRD)、氢气-程序升温还原(H2-TPR)和循环伏安法(CV)等技术对其进行了表征, 考察了不同方法制备的CeO2载体对CuO/CeO2水煤气变换(WGS)催化剂的结构、氧化-还原性能、催化活性和稳定性的影响. 结果表明, 它们的催化活性和稳定性顺序都是CuO/CeO2-A>CuO/CeO2-B>CuO/CeO2-C. 联系表征结果, CuO/CeO2催化剂的活性与催化剂中CuO的颗粒度、CuO的微观应力和中等大小且与二氧化铈相互作用的CuO的数量等有关, 而这些因素很大程度上受CeO2载体本身的热稳定性的影响. 根据CV中扫描次数的增加, Cu2+←→Cu0氧化还原峰面积减小, 推断CuO/CeO2催化剂在一定条件下氧化还原是不可逆的, 这可能是其在反应气氛下经受温度循环之后活性降低的原因.