Daojin Zhou

Superaerophobic Ultrathin Ni–Mo Alloy Nanosheet Array from In Situ Topotactic Reduction for Hydrogen Evolution Reaction

Hydrogen evolution reaction (HER) has prospect to becoming clean and renewable technology for hydrogen production and Ni-Mo alloy is among the best HER catalysts in alkaline electrolytes. Here, an in situ topotactic reduction method to synthesize ultrathin 2D Ni-Mo alloy nanosheets for electrocatalytic hydrogen evolution is reported. Due to its ultrathin structure and tailored composition, the as-synthesized Ni-Mo alloy shows an overpotential of 35 mV to reach a current density of 10 mA cm-2 , along with a Tafel slope of 45 mV decade-1 , demonstrating a comparable intrinsic activity to state-of-art commercial Pt/C catalyst. Besides, the vertically aligned assemble structure of the 2D NiMo nanosheets on conductive substrate makes the electrode superaerophobic, thus leading to much faster bubble releasing during HER process and therefore shows faster mass transfer behavior at high current density as compared with drop drying Pt/C catalyst on the same substrate. Such in situ topotactic conversion finds a way to design and fabricate low-cost, earth-abundant non-noble metal based ultrathin 2D nanostructures for electrocatalytic issues.

Effects of redox-active interlayer anions on the oxygen evolution reactivity of NiFe-layered double hydroxide nanosheets

Nickel-iron layered double hydroxide (NiFe-LDH) nanosheets have shown optimal oxygen evolution reaction (OER) performance; however, the role of the intercalated ions in the OER activity remains unclear. In this work, we show that the activity of the NiFe-LDHs can be tailored by the intercalated anions with different redox potentials. The intercalation of anions with low redox potential (high reducing ability), such as hypophosphites, leads to NiFe-LDHs with low OER overpotential of 240 mV and a small Tafel slope of 36.9 mV/dec, whereas NiFe-LDHs intercalated with anions of high redox potential (low reducing ability), such as fluorion, show a high overpotential of 370 mV and a Tafel slope of 80.8 mV/dec. The OER activity shows a surprising linear correlation with the standard redox potential. Density functional theory calculations and X-ray photoelectron spectroscopy analysis indicate that the intercalated anions alter the electronic structure of metal atoms which exposed at the surface. Anions with low standard redox potential and strong reducing ability transfer more electrons to the hydroxide layers. This increases the electron density of the surface metal sites and stabilizes their high-valence states, whose formation is known as the critical step prior to the OER process.

A highly-efficient oxygen evolution electrode based on defective nickel-iron layered double hydroxide

Exploring efficient and cost-effective electrocatalysts for oxygen evolution reaction (OER) is critical to water splitting. While nickel-iron layered double hydroxide (NiFe LDH) has been long recognized as a promising non-precious electrocatalyst for OER, its intrinsic activity needs further improvement. Herein, we design a highly-efficient oxygen evolution electrode based on defective NiFe LDH nanoarray. By combing the merits of the modulated electronic structure, more exposed active sites, and the conductive electrode, the defective NiFe LDH electrocatalysts show a low onset potential of 1.40 V (vs. RHE). An overpotential of only 200 mV is required for 10 mA cm−2, which is 48 mV lower than that of pristine NiFe-LDH. Density functional theory plus U (DFT+U) calculations are further employed for the origin of this OER activity enhancement. We find the introduction of oxygen vacancies leads to a lower valance state of Fe and the narrowed bandgap, which means the electrons tend to be easily excited into the conduction band, resulting in the lowered reaction overpotential and enhanced OER performance.摘要探索低成本高效率的析氧电极对于工业电解水技术的发展至关重要. 尽管镍铁水滑石已被公认为是一种高效析氧的非贵金属催化剂, 但其本征活性还有待进一步提高. 本研究通过将氧空位缺陷引入镍铁水滑石, 设计出一种低成本高效率的析氧电极. 通过精确电子结构调控, 暴露更多活性位点, 提高电极导电性, 富缺陷镍铁水滑石电极展现出1.40 V (vs. RHE)的低起峰电位. 同时, 它仅需200 mV过电势就能达到10 mA cm−2的电流密度, 这相比未经处理的镍铁水滑石降低了48 mV. 我们进一步通过密度泛函理论计算发现, 氧空位缺陷的引入使Fe的价态降低, 带隙减小, 使得催化过程中电子更容易被激发到导带中, 从而降低反应过电势并使析氧活性增强.

Layered double hydroxides with atomic-scale defects for superior electrocatalysis

Atomic composition tuning and defect engineering are effective strategies toenhance the catalytic performance of multicomponent catalysts by improvingthe synergetic effect; however, it remains challenging to dramatically tune the active sites on multicomponent materials through simultaneous defect engineeringat the atomic scale because of the similarities of the local environment. Herein,using the oxygen evolution reaction (OER) as a probe reaction, we deliberatelyintroduced base-soluble Zn(II) or Al(III) sites into NiFe layered double hydroxides(LDHs), which are one of the best OER catalysts. Then, the Zn(II) or Al(III) siteswere selectively etched to create atomic M(II)/M(III) defects, which dramaticallyenhanced the OER activity. At a current density of 20 mA·cm−2, only 200 mV overpotential was required to generate M(II) defect-rich NiFe LDHs, which is the best NiFe-based OER catalyst reported to date. Density functional theory(DFT) calculations revealed that the creation of dangling Ni–Fe sites (i.e., unsaturated coordinated Ni–Fe sites) by defect engineering of a Ni–O–Fe site at the atomic scale efficiently lowers the Gibbs free energy of the oxygen evolutionprocess. This defect engineering strategy provides new insights into catalysts atthe atomic scale and should be beneficial for the design of a variety of catalysts.

Aligned N-doped carbon nanotube bundles with interconnected hierarchical structure as an efficient bi-functional oxygen electrocatalyst

The fabrication of cost effective and efficient electrocatalysts with functional building blocks to replace noble metal ones is of great importance for energy related applications yet remains a great challenge. Herein, we report the fabrication of a hierarchical structure containing CNTs/graphene/transition-metal hybrids (h-NCNTs/Gr/TM) with excellent bifunctional oxygen electrocatalytic activity. The synthesis was rationally designed by the growth of shorter nitrogen-doped CNTs (S-NCNTs) on longer NCNTs arrays (L-NCNTs), while graphene layers were in situ generated at their interconnecting sites. The hybrid material shows excellent OER and ORR performance, and was also demonstrated to be a highly active bifunctional catalyst for Zn–air batteries, which could be due to rapid electron transport and full exposure of active sites in the hierarchical structure.

Activating basal plane in NiFe layered double hydroxide by Mn2+ doping for efficient and durable oxygen evolution reaction

Foreign metal ions with reducing ability were doped into NiFe layered double hydroxides (NiFe-LDHs) to activate the basal plane in NiFe-LDHs for oxygen evolution reaction (OER). Mn2+-Doped NiFe-LDH array electrode yields a low onset potential of 1.41 V and exhibits outstanding stability. The study herein illustrates a new dimension of electronic structure regulation and promises further optimization of highly efficient electrocatalysts.

Boosting Oxygen Reaction Activity by Coupled Sulfides for High-Performance Rechargeable Metal-Air Battery

Sluggish oxygen electrochemistry including both oxygen evolution reactions (OER) and oxygen reduction reactions (ORR) greatly restricts the performance of rechargeable metal–air battery. Herein, we couple NiFe sulfide (NiFeS2) with S-doped graphene oxide (S-GO) via a simultaneous sulfurization strategy to significantly improve the OER and ORR activities. The NiFeS2/S-GO on glassy carbon yields an OER current density of 10 mA cm−2 at 1.47 V and an ORR half-wave potential at 0.74 V (vs. RHE), giving an overvoltage difference as low as 0.73 V. When assembled in a rechargeable Zn–air battery, the battery with NiFeS2/S-GO air electrode exhibits a steady charging potential (1.98 V) with very little decay in discharging potential (from 1.20 to 1.17 V) for 180 charging–discharging cycles at 10 mA cm−2. Our study provides new insights for the design of efficient bifunctional oxygen electrocatalysts for high-performance energy conversion and storage devices.

Introducing Fe2+ into Nickel–Iron Layered Double Hydroxide: Local Structure Modulated Water Oxidation Activity

Exploring materials with regulated local structures and understanding how the atomic motifs govern the reactivity and durability of catalysts are a critical challenge for designing advanced catalysts. Herein we report the tuning of the local atomic structure of nickel-iron layered double hydroxides (NiFe-LDHs) by partially substituting Ni2+ with Fe2+ to introduce Fe-O-Fe moieties. These Fe2+ -containing NiFe-LDHs exhibit enhanced oxygen evolution reaction (OER) activity with an ultralow overpotential of 195u2005mV at the current density of 10u2005mAu2009cm-2 , which is among the best OER catalytic performance to date. In-situ X-ray absorption, Raman, and electrochemical analysis jointly reveal that the Fe-O-Fe motifs could stabilize high-valent metal sites at low overpotentials, thereby enhancing the OER activity. These results reveal the importance of tuning the local atomic structure for designing high efficiency electrocatalysts.