Bimetallic cobalt-nickel coordination polymer electrocatalysts for enhancing oxygen evolution reaction

Coordination polymers（CPs） have great potential to be used in electrocatalysis owing to their designable compositions and structures. It is highly challenging to apply CPs as electrocatalysts for oxygen evolution reaction（OER） on account of insufficient catalytic efficiency and relatively poor stability of current electrocatalysts. Herein, through a mixed-metal strategy, one-dimensional Co_xNi_1-x-HIPA with dual active sites was synthesized and studied for OER electrocatalyst...     

Heterogeneous luminescence of oxides in impact recombination of oxygen atoms

Surface luminescence of oxides is excited by oxygen atoms in acts of impact recombination. The elementary excitation mechanism is due to adiabatic shift of the chemisorption complex to a nonequilibrium electronic state. At low flux densities of free atoms the charged form of adsorbed oxygen atoms is responsible for luminescence excitation.

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The nature of synergistic effects in transition metal oxides/in-situ intermediate-hydroxides for enhanced oxygen evolution reaction

Oxygen evolution reaction is highly important for hydrogen production via water splitting but requires ～0.22 V onset overpotential, resulting in at least 15% extra energy consumption even utilized with the benchmark hetero-doped transition-metal hydroxide catalysts. The lack of fundamental understanding on catalyst behaviour and on synergistic mechanisms limit the breakthrough for material design. Here, we systematically summarise a variety of investigations and arguments on the mechanism from the microscale (optimal octahedral intermediate with six M?O coordination) to atomic scale (the active site behaviour). The electron–orbital scale (e_g) is further described for the intrinsic OER activity. The synergistic effect may also lead to a short-cut pathway of lattice-oxygen-mediated mechanism to achieve a smaller overpotential. This review provides a theoretical reference for the design of advanced catalysts.     

Sr掺杂钙钛矿体系中高活性氧析出反应机制（英文）

析氧反应(oxygen evolutionreaction OER)是电催化分解水、二氧化碳还原、金属-空气电池以及燃料电池等能源转化及存储技术的关键过程,因此被广泛关注和研究.OER过程涉及四个电子转移,是动力学迟滞过程,具有较大的过电位,此外OER催化反应的同时也可能改变电极表面状态,故其机理的研究十分困难.设计和开发高效OER催化剂材料是提高电解水效率的关键.最近的研究发现反应后催化剂表面会发生重构,进而形成无定形层,该无定形层被认为会改善催化活性.我们的前期研究也发现了表面不饱和配位无定形层的存在,但对于重构机制尚没有明确的解释.本文在上述研究基础上,利用熔盐法合成了一系列具有多孔结构的不同Sr含量的LaCo0.8Fe0.2O3-δ钙钛矿材料,通过电化学装置测试其催化活性,并采用X射线衍射(XRD)、扫描电子显微镜(SEM)、高分辨透射电镜(HRTEM)、比表面积测试(BET)和软硬X射线吸收谱技术等表征手段对其进行了深入探索.XRD测试结果表明,Sr掺杂LaCo0.8Fe0.2O3-δ钙钛矿材料的主峰随着Sr含量增加向低角度偏移,这是由于Sr的离子半径较La的大.SEM和BET测试结果表明,不同Sr含量样品均表现出多孔的钙钛矿结构,并具有相似的比表面积,说明Sr含量变化不影响催化剂的形貌和比表面积.利用硬X射线吸收谱对体相Co和Fe元素的价态进行了研究,发现随着Sr含量的增加,Co和Fe离子的价态没有明显变化.类似地,利用软X射线吸收谱对表面层Co和Fe价态进行的研究发现,Co和Fe均表现出+3价,但在氧元素的K边吸收谱上观察到明显的氧空穴存在.电化学测试结果表明,催化剂的活性随Sr含量增加而增大.总之,随着Sr的掺杂,催化剂形貌及活性元素价态均无明显变化,但样品的电化学性能却发生了明显改善,这意味着尚有其它因素影响催化剂活性.利用HRTEM对OER反应前后的样品进行了形貌分析,发现在OER反应后Sr掺杂的催化剂表面出现了明显的无定形层,而无Sr掺杂的样品反应前后几乎未观察到表面形貌的变化.由此我们推断,Sr掺杂可诱导催化剂表面出现无定形层,进而提高OER反应活性.因此,在LaCo0.8Fe0.2O3-δ钙钛矿材料体系中,Sr掺杂是影响OER催化剂表面重构和制约催化活性的关键.     

Formation of oxygen atoms in the reaction of chlorine atoms with ozone

Oxygen atoms are detected by NO + O + M chemiluminescence as a secondary product of the reaction between Cl and O₃. The mechanism Cl + O₃ → ClO + O₂(¹Σ⁺_g), O₂(¹Σ⁺_g) + O₃ → O₂ + O₂ + O is proposed to account for the oxygen atom formation. The branching ratio to the O₂(¹Σ⁺_g) product in the reaction of Cl with O₃ is estimated to be in the range (0.1–0.5) x 10^?2.     

Electrodeposition of (hydro)oxides for an oxygen evolution electrode

Electrochemical water splitting is a promising technology for hydrogen production and sustainable energy conversion, but the electrolyzers that are currently available do not have anodic electrodes that are robust enough and highly active for the oxygen evolution reaction (OER). Electrodeposition provides a feasible route for preparing freestanding OER electrodes with high active site utilization, fast mass transport and a simple fabrication process, which is highly attractive from both academic and commercial points of view. This minireview focuses on the recent electrodeposition strategies for metal (hydro)oxide design and water oxidation applications. First, the intrinsic advantages of electrodeposition in comparison with traditional technologies are introduced. Then, the unique properties and underlying principles of electrodeposited metal (hydro)oxides in the OER are unveiled. In parallel, illustrative examples of the latest advances in materials structural design, controllable synthesis, and mechanism understanding through the electrochemical synthesis of (hydro)oxides are presented. Finally, the latest representative OER mechanism and electrodeposition routes for OER catalysts are briefly overviewed. Such observations provide new insights into freestanding (hydro)oxides electrodes prepared via electrodeposition, which show significant practical application potential in water splitting devices. We hope that this review will provide inspiration for researchers and stimulate the development of water splitting technology.

This minireview looks at recent electrodeposition strategies for metal (hydro)oxide design and water oxidation applications, unveiling the unique properties and underlying principles of electrodeposited metal (hydro)oxides in the OER.     

A novel composite electrode for oxygen evolution reaction

FeOOH nanowires were prepared and characterized with X-ray diffraction spectroscopy and scanning electron microscopy. A composite electrode consisting of FeOOH and Ni foam (FeOOH/Ni-foam) was fabricated, and its catalytic performance for oxygen evolution reaction (OER) was evaluated and compared with nanowire NiCo₂O₄/Ni-foam electrode. The mass current density of OER on FeOOH/Ni-foam is around three times of that on NiCo₂O₄/Ni-foam. Ni foam played a key role for the high activity of the FeOOH/Ni-foam. A synergistic mechanism of FeOOH and Ni was proposed to account for the superior catalytic performance of the FeOOH/Ni-foam electrode. Considering the low cost, abundant resource and environment-benign property of FeOOH, the FeOOH/Ni-foam electrode would be a promising anode for OER.     

Single-crystalline layered double hydroxides with rich defects and hierarchical structure by mild reduction for enhancing the oxygen evolution reaction

The oxygen evolution reaction(OER) with sluggish reaction kinetics and large overpotential is the critical reaction in water splitting that is promising for energy storage and conversion. Layered double hydroxides(LDHs), due to their unique lamellar structure and flexibility of chemical component, are very competing material candidates for OER. Herein, the morphology structure and the electronic structure of LDHs were simultaneously tuned to improve the OER catalytic activity by mild solvothermal reduction using ethylene glycol. The increased surface area, the introduction of oxygen vacancies and the construction of hierarchical structure greatly enhanced the electro-catalytic activity of LDHs for OER. The as-prepared LDHs showed a lower over-potential as low as 276 mV at a current density of 10 mA cm~(-2), and a small Tafel slope of 40.3 mV dec~(-1) accompanied with good stability. This work provides an efficient way to the design and optimization of advanced catalysts in the future.     

Carambola-like metal-organic frameworks for high-performance electrocatalytic oxygen evolution reaction

Hydrogen production by electrocatalytic water splitting promises a green and sustainable technology to address serious energy crisis and environmental pollution [1]. As well known, the process of electrocatalytic water splitting is composed of two half reaction, i.e. oxygen evolution reaction (OER) at the anode and hydrogen evolution reaction (HER) at the cathode [2].     

Co porphyrin-based metal-organic framework for hydrogen evolution reaction and oxygen reduction reaction

Constructing molecule@support composites is an attractive strategy to realize heterogeneous molecular electrocatalysis. Herein, we synthesized metal-organic framework (MOF)-supported molecular catalysts for hydrogen evolution and oxygen reduction reaction (HER/ORR). Ligand exchange strategy was used to prepare molecule@support hybrids due to the same functional group. A series of hybrids were obtained using Co porphyrin (1) and different MOFs including MIL-88(Fe), MOF-5(NiCo) and UIO-66(Zr). The 1@MOF-5(NiCo) had the best HER and ORR activity compared with 1@MIL-88(Fe) and 1@MOF-5(NiCo). These hybrids also exhibited tunable selectivity for ORR with four-electron process, which can be attributed to the synergistic effect of porphyrin molecules and MOFs. This work provides a possibility for molecular catalysts to improve activity of HER and tune selectivity of ORR.     

碳载氧化锰表面氧还原反应路径研究(英文)

氧还原反应(ORR)是一个复杂的过程,尤其在碱性电解液中,炭载型催化剂表面的ORR路径尤为复杂,因为碳本身可以催化ORR以二电子转移过程发生,产生过氧化氢,继而过氧化氢或者发生化学分解生成氧气(HODR),或者发生电化学还原生成OH(HORR).本文详细研究了ORR在常用氧化锰催化剂表面的反应路径.通过比较HODR和HORR的转换频率发现,尽管利用旋转环盘电极方法得到的表观电子转移数接近4,真实的ORR主要是2电子过程,反应生成的过氧化氢继而大部分发生化学分解生成氧气.该结果有助于理解碱性电解质中炭载型过渡金属氧化物电催化剂对ORR的催化行为.     

Recent advances in metal-organic frameworks for oxygen evolution reaction electrocatalysts

The anodic oxygen evolution reaction(OER) can be combined with various cathodic reactions to enable the electrochemical synthesis of diverse chemicals and fuels, particularly in water electrolysis for hydrogen production. It is however exhibiting a high overpotential due to the sluggish four-electron transfer process, which is considered the decisive reaction in energy conversion systems. In recent years, metal-organic frameworks(MOFs) have emerged as the ideal catalysts for accelerating OER. Th...     

铂基氧还原电催化剂的结构演变

质子交换膜燃料电池的商业化有望在不久的将来实现更清洁的能源社会.然而,氧还原反应缓慢的反应动力学和苛刻的条件对质子交换膜燃料电池的寿命和成本产生了巨大的挑战.之前大多数铂基催化剂的设计都将重点更多地放在提高活性上.随着质子交换膜燃料电池的商业化,寿命问题也受到了更多的关注.对整个生命周期中结构演变进行深入地了解,有助于...     

On the rate of the reaction of ammonia with oxygen atoms

Absolute rate constants for the reaction of O(³P) with ammonia were measured over the temperature range 448–841 K by means of a laser photolysis-chemiluminescence technique. The data were fitted with the following Arrhenius expression: k = 3.42 × 10^?11 exp[-(9000 ± 600 cal/mole)/RT] cm³ molecule^?1 s^?1. Comparisons with literature data and predictions based upon the extrapolations to higher temperatures found in combustion are presented. The extrapolations are in agreement with recent shock-tube data and indicate that this reaction is more important in high-temperature ammonia oxidation than previously believed.     

Electropolymerization of cobalt porphyrins and corroles for the oxygen evolution reaction

Developing large-scale electrocatalysts using molecular complexes for the oxygen evolution reaction (OER) is of great importance. Herein, four cobalt porphyrins and corroles are deposited on electrode substrates using a simple and fast electropolymerization method. Our results showed that Co-1-P@CC, formed by electropolymerizing Co tetrakis(p-N-pyrrolylphenyl)porphyrin (Co-1-P) on carbon cloth (CC), is the most active OER catalyst in the examined Co porphyrins and corroles in alkaline aqueous solutions by displaying an onset overpotential of 380 mV. Long-term electrolysis tests confirmed the stability of these electropolymerized films by functioning as OER electrocatalysts.     

Electrocatalytic behavior of electroless Ni-P alloys for the oxygen evolution reaction

The structural and morphological characteristics of electroless nickel phosphorous films (P content from 4.0 to 13.8 at %) are described. Different treatments such as heat (400°C, 1 h) or electrochemical (anodizing at 0.5 V vs. SCE followed by multi-cycle polarization) are employed and their effect on the alloys properties is analyzed using x-ray diffraction and atomic force microscopy. Information on the performance of the as-deposited and treated electroless Ni-P coatings as anodes for oxygen evolution reaction, in alkaline media, is taken from the steady state polarization curves and the correspondent Tafel slopes. The data shows the importance of the deposit crystalline nature and of the electrochemical treatment on the formation of β-Ni(OH)₂ and subsequently β-Ni(OOH), crucial for obtaining Ni-P films with good electrocatalytic properties. Published in Russian in Elektrokhimiya, 2006, Vol. 42, No. 12, pp. 1427–1434. Based on the report delivered at the 8th International Frumkin Symposium “Kinetics of the Electrode Processes.” October 18–22, 2005, Moscow. The text was submitted by the authors in English.     

Electrocatalyst design for promoting two-electron oxygen reduction reaction: Isolation of active site atoms

Selective two-electron (2 e^?) pathway oxygen reduction reaction (ORR) has gained prominence for enabling small-scale, on-site electrochemical H₂O₂ production and has emerged as a promising alternative to the conventional anthraquinone process. The rational design of catalysts that can suppress the competing four-electron pathway ORR is critical. This review highlights catalyst design strategies for promoting the selective 2 e^? pathway ORR, including alloying with inert metals, partial surface poisoning, and generating atomically dispersed sites. The major results and advances, as well as unresolved challenges are summarized.     

Surface and adsorption studies of high surface area oxides

Modern FT-IR spectroscopy offers an ample potential for the study of adsorption and desorption processes on high surface area materials. Three examples will be presented here: (i) the thermal desorption of H₂O from SiO₂, (ii) the chemisorption and physisorption of H₂O on SiO₂, (iii) the interaction of NH₃ with OH groups on MgO surfaces.