Doping‐Induced Amorphization,Vacancy, and Gradient Energy Band in SnS2 Nanosheet Arrays for Improved Photoelectrochemical Water Splitting

Photoelectrochemical (PEC) water splitting is a promising strategy to convert solar energy into hydrogen fuel. However, the poor bulk charge‐separation ability and slow surface oxygen evolution reaction (OER) dynamics of photoelectrodes impede the performance. We construct In‐ and Zn/In‐doped SnS₂ nanosheet arrays through a hydrothermal method. The doping induces the simultaneous formation of an amorphous layer, S vacancies, and a gradient energy band. This leads to elevated carrier concentrations, an increased number of surface‐reaction sites, accelerated surface‐OER kinetics, and an enhanced bulk‐carrier separation efficiency with a decreased recombination rate. This efficient doping strategy allows to manipulate the morphology, crystallinity, and band structure of photoelectrodes for an improved PEC performance.     

Doping‐Induced Amorphization,Vacancy, and Gradient Energy Band in SnS2 Nanosheet Arrays for Improved Photoelectrochemical Water Splitting

Photoelectrochemical (PEC) water splitting is a promising strategy to convert solar energy into hydrogen fuel. However, the poor bulk charge‐separation ability and slow surface oxygen evolution reaction (OER) dynamics of photoelectrodes impede the performance. We construct In‐ and Zn/In‐doped SnS₂ nanosheet arrays through a hydrothermal method. The doping induces the simultaneous formation of an amorphous layer, S vacancies, and a gradient energy band. This leads to elevated carrier concentrations, an increased number of surface‐reaction sites, accelerated surface‐OER kinetics, and an enhanced bulk‐carrier separation efficiency with a decreased recombination rate. This efficient doping strategy allows to manipulate the morphology, crystallinity, and band structure of photoelectrodes for an improved PEC performance.     

Ultrathin Spinel‐Structured Nanosheets Rich in Oxygen Deficiencies for Enhanced Electrocatalytic Water Oxidation

Electrochemical water splitting is a clean technology for H₂ fuels, but greatly hindered by the slow kinetics of the oxygen evolution reaction (OER). Herein, a series of spinel‐structured nanosheets with oxygen deficiencies and ultrathin thicknesses were designed to increase the reactivity and the number of active sites of the catalysts, which were then taken as an excellent platform for promoting the water oxidation process. Theoretical investigations showed that the oxygen vacancies confined in the ultrathin nanosheet could lower the adsorption energy of H₂O, leading to increased OER efficiency. As expected, the NiCo₂O₄ ultrathin nanosheets rich in oxygen vacancies exhibited a large current density of 285 mA cm^?2 at 0.8 V and a small overpotential of 0.32 V, both of which are superior to the corresponding values of bulk samples or samples with few oxygen deficiencies and even higher than those of most reported non‐precious‐metal catalysts. This work should provide a new pathway for the design of advanced OER catalysts.     

Plasma‐Engraved Co3O4 Nanosheets with Oxygen Vacancies and High Surface Area for the Oxygen Evolution Reaction

Co₃O₄, which is of mixed valences Co²⁺ and Co³⁺, has been extensively investigated as an efficient electrocatalyst for the oxygen evolution reaction (OER). The proper control of Co²⁺/Co³⁺ ratio in Co₃O₄ could lead to modifications on its electronic and thus catalytic properties. Herein, we designed an efficient Co₃O₄‐based OER electrocatalyst by a plasma‐engraving strategy, which not only produced higher surface area, but also generated oxygen vacancies on Co₃O₄ surface with more Co²⁺ formed. The increased surface area ensures the Co₃O₄ has more sites for OER, and generated oxygen vacancies on Co₃O₄ surface improve the electronic conductivity and create more active defects for OER. Compared to pristine Co₃O₄, the engraved Co₃O₄ exhibits a much higher current density and a lower onset potential. The specific activity of the plasma‐engraved Co₃O₄ nanosheets (0.055 mA cm^?2_BET at 1.6 V) is 10 times higher than that of pristine Co₃O₄, which is contributed by the surface oxygen vacancies.     

Tailoring Oxygen Vacancy on Co3O4 Nanosheets with High Surface Area for Oxygen Evolution Reaction?

Electrochemical water splitting requires efficient water oxidation catalysts to accelerate the sluggish kinetics of water oxidation reaction. Here, we designed an efficient Co₃O₄ electrocatalyst using a pyrolysis strategy for oxygen evolution reaction (OER). Morphological characterization confirmed the ultra-thin structure of nanosheet. Further, the existence of oxygen vacancies was obviously evidenced by the X-ray photoelectron spectroscopy and electron spin resonance spectroscopy. The increased surface area of Co₃O₄ ensures more exposed sites, whereas generated oxygen vacancies on Co₃O₄ surface create more active defects. The two scenarios were beneficial for accelerating the OER across the interface between the anode and electrolyte. As expected, the optimized Co₃O₄ nanosheets can catalyze the OER efficiently with a low overpotential of 310 mV at current density of 10 mA/cm² and remarkable long-term stability in 1.0 mol/L KOH.     

Double Perovskite LaFexNi1−xO3 Nanorods Enable Efficient Oxygen Evolution Electrocatalysis

Perovskite‐based electrocatalysts are one of the most promising materials for oxygen evolution reaction (OER), but their activity and durability are still far from desirable. Herein, we demonstrate that the double perovskite LaFe_xNi_1?xO₃ (LFNO) nanorods (NRs) can be adopted as highly active and stable OER electrocatalysts. The optimized LFNO‐II NRs with Ni/Fe ratio of 8:2 achieve a low overpotential of 302 mV at 10 mA cm^?2 and a small Tafel slope of 50 mV dec^?1, outperforming those of the commercial Ir/C. The LFNO‐II NRs also show high OER stability with slight current decrease after 20 h. The enhanced activity is explained by the improved surface area, tailored electronic structure as well as strong hybridization between O and Ni.     

Unveiling the Activity and Stability Origin of BiVO4 Photoanodes with FeNi Oxyhydroxides for Oxygen Evolution

Understanding the origin of formation and active sites of oxygen evolution reaction (OER) cocatalysts is highly required for solar photoelectrochemical (PEC) devices that generate hydrogen efficiently from water. Herein, we employed a simple pH-modulated method for in situ growth of FeNi oxyhydroxide ultrathin layers on BiVO₄ photoanodes, resulting in one of the highest currently known PEC activities of 5.8 mA cm⁻² (1.23 V_RHE, AM 1.5 G) accompanied with an excellent stability. More importantly, both comparative experiments and density functional theory (DFT) studies clearly reveal that the selective formation of Bi−O−Fe interfacial bonds mainly contributes the enhanced OER activities, while the construction of V−O−Ni interfacial bonds effectively restrains the dissolution of V⁵⁺ ions and promotes the OER stability. Thereby, the synergy between iron and nickel of FeNi oxyhydroxides significantly improved the PEC water oxidation properties of BiVO₄ photoanodes.     

A co-activation strategy for enhancing the performance of hematite in photoelectrochemical water oxidation

Hematite(α-Fe_2O_3) is a promising photoanode for photoelectrochemical(PEC) water splitting.However,the severe charge recombination and sluggish water oxidation kinetics extremely limit its use in photohydrogen conversion.Herein,a co-activation strategy is proposed,namely through phosphorus(P)doping and the loading of CoAl-layered double hydroxides(CoAl-LDHs) cocatalysts.Unexpectedly,the integrated system,CoAl-LDHs/P-Fe_2O_3 photoanode,exhibits an outstanding photocurrent density of 1.56 mA/cm~2 at 1.23 V(vs.reversible hydrogen electrode,RHE),under AM 1.5 G,which is 2.6 times of pureα-Fe_2O_3.Systematic studies reveal that the remarkable PEC performance is attributed to accelerated surface OER kinetics and enhanced carrier separation efficiency.This work provides a feasible strategy to enhance the PEC performance of hematite photoanodes.     

Remarkable Oxygen‐Evolution Activity of a Perovskite Oxide from the Ca2−xSrxFe2O6−δ Series

Herein in we report the unprecedented catalytic activity of an iron‐based oxygen‐deficient perovskite for the oxygen‐evolution reaction (OER). The systematic trends in OER activity as a function of composition, defect‐order, and electrical conductivity have been demonstrated, leading to a methodical increase in OER catalytic activity: Ca₂Fe₂O_6?δ<CaSrFe₂O_6?δ<Sr₂Fe₂O_6?δ. Sr₂Fe₂O_6?δ also has the highest electrical conductivity and a unique type of defect‐order. In conventional experiments using glassy carbon electrode, Sr₂Fe₂O_6?δ shows better OER activity than the current state of the art catalysts, Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3?δ and RuO₂. It also offers a high intrinsic electrical conductivity, which allows it to act as a catalyst without the need for glassy carbon electrode or carbon powder. Pure disks of this material exhibit an outstanding activity for OER, without any additives or need for electrode preparation.     

Folded nanosheet-like Co<Subscript>0.85</Subscript>Se array for overall water splitting

Active, stable, and earth-abundant bifunctional electrocatalyst for overall water splitting is pivotal to actualize large-scale water splitting via electrolysis. In this work, the hierarchical folded nanosheet-like Co_0.85Se array on Ni foam is constructed by liquid-phase chemical conversion with cobalt precursor nanorod array. It can serve as an efficient bifunctional electrocatalyst for both oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) in alkaline electrolyte, with a current density of 10 mA cm^?2 at overpotential of 232 mV for OER and 129 mV for HER and Tafel slope of 78.9 mV dec^?1 for OER and 95.0 mV dec^?1 for HER, respectively. The two-electrode alkaline water electrolyzer utilizing this folded nanosheet-like Co_0.85Se array as both anode and cathode toward overall water splitting offered a current of 10 mA cm^?2 at a cell voltage of 1.60 V. This work explores an efficient and low-cost electrocatalyst for overall water splitting application in alkaline electrolytes.     

SrNb0.1Co0.7Fe0.2O3−δ Perovskite as a Next‐Generation Electrocatalyst for Oxygen Evolution in Alkaline Solution

The perovskite SrNb_0.1Co_0.7Fe_0.2O_3?δ (SNCF) is a promising OER electrocatalyst for the oxygen evolution reaction (OER), with remarkable activity and stability in alkaline solutions. This catalyst exhibits a higher intrinsic OER activity, a smaller Tafel slope and better stability than the state‐of‐the‐art precious‐metal IrO₂ catalyst and the well‐known BSCF perovskite. The mass activity and stability are further improved by ball milling. Several factors including the optimized e_g orbital filling, good ionic and charge transfer abilities, as well as high OH^? adsorption and O₂ desorption capabilities possibly contribute to the excellent OER activity.     

Bimetallic Metal‐Organic Framework‐Derived Nanosheet‐Assembled Nanoflower Electrocatalysts for Efficient Oxygen Evolution Reaction

Non‐noble metal‐based metal–organic framework (MOF)‐derived electrocatalysts have recently attracted great interest in the oxygen evolution reaction (OER). Here we report a facile synthesis of nickel‐based bimetallic electrocatalysts derived from 2D nanosheet‐assembled nanoflower‐like MOFs. The optimized morphologies and large Brunauer–Emmett–Teller (BET) surface area endow FeNi@CNF with efficient OER performance, where the aligned nanosheets can expose abundant active sites and benefit electron transfer. The complex nanoflower morphologies together with the synergistic effects between two metals attributed to the OER activity of the Ni‐based bimetallic catalysts. The optimized FeNi@CNF afforded an overpotential of 356 mV at a current density of 10 mA cm^?2 with a Tafel slope of 62.6 mV dec^?1, and also exhibited superior durability with only slightly degradation after 24 hours of continuous operation. The results may inspire the use of complex nanosheet‐assembled nanostructures to explore highly active catalysts for various applications.     

Nickel Doping in Atomically Thin Tin Disulfide Nanosheets Enables Highly Efficient CO2 Reduction

Engineering electronic properties by elemental doping is a direct strategy to design efficient catalysts towards CO₂ electroreduction. Atomically thin SnS₂ nanosheets were modified by Ni doping for efficient electroreduction of CO₂. The introduction of Ni into SnS₂ nanosheets significantly enhanced the current density and Faradaic efficiency for carbonaceous product relative to pristine SnS₂ nanosheets. When the Ni content was 5 atm %, the Ni‐doped SnS₂ nanosheets achieved a remarkable Faradaic efficiency of 93 % for carbonaceous product with a current density of 19.6 mA cm^?2 at ?0.9 V vs. RHE. A mechanistic study revealed that the Ni doping gave rise to a defect level and lowered the work function of SnS₂ nanosheets, resulting in the promoted CO₂ activation and thus improved performance in CO₂ electroreduction.     

Tailoring Ion Ordering in Perovskite Oxide for High-Temperature Oxygen Evolution Reaction

Perovskites exhibit excellent high-temperature oxygen evolution reaction (OER) activities as the anodes of solid oxide electrolysis cells (SOECs). However, the relationship between ion ordering and OER performances is rarely investigated. Herein, a series of PrBaCo_2−xFe_xO_5+δ perovskites with tailored ion orderings are constructed. Physicochemical characterizations and density functional theory calculations confirm that the oxygen bulk migration and surface transport capacities as well as the OER activities are promoted by the A-site cation ordering, but weakened by the oxygen vacancy ordering. Hence, SOEC with the A-site-ordered and oxygen-vacancy-disordered PrBaCo₂O_5+δ anode exhibits the highest performance of 3.40 A cm⁻² at 800 °C and 2.0 V. This work sheds light on the critical role of ion orderings in the high-temperature OER performance and paves a new way for screening novel anode materials of SOECs.     

The Role of Surface States in the Oxygen Evolution Reaction on Hematite

Hematite (α‐Fe₂O₃) is an extensively investigated semiconductor for photoelectrochemical (PEC) water splitting. The nature and role of surface states on the oxygen evolution reaction (OER) remain however elusive. First‐principles calculations were used to investigate surface states on hematite under photoelectrochemical conditions. The density of states for two relevant hematite terminations was calculated, and in both cases the presence and the role of surface states was rationalized. Calculations also predicted a Nerstian dependence on the OER onset potential on pH, which was to a very good extent confirmed by PEC measurements on hematite model photoanodes. Impedance spectroscopy characterization confirmed that the OER takes place via the same surface states irrespective of pH. These results provide a framework for a deeper understanding of the OER when it takes place via surface states.     

Ultrathin FeOOH Nanolayers with Abundant Oxygen Vacancies on BiVO4 Photoanodes for Efficient Water Oxidation

Photoelectrochemical (PEC) water splitting is a promising method for storing solar energy in the form of hydrogen fuel, but it is greatly hindered by the sluggish kinetics of the oxygen evolution reaction (OER). Herein, a facile solution impregnation method is developed for growing ultrathin (2 nm) highly crystalline β‐FeOOH nanolayers with abundant oxygen vacancies on BiVO₄ photoanodes. These exhibited a remarkable photocurrent density of 4.3 mA cm^?2 at 1.23 V (vs. reversible hydrogen electrode (RHE), AM 1.5 G), which is approximately two times higher than that of amorphous FeOOH fabricated by electrodeposition. Systematic studies reveal that the excellent PEC activity should be attributed to their ultrathin crystalline structure and abundant oxygen vacancies, which could effectively facilitate the hole transport/trapping and provide more active sites for water oxidation.     

FeNi Nanoparticles Coated on N-doped Ultrathin Graphene-like Nanosheets as Stable Bifunctional Catalyst for Zn-Air Batteries

High-performance and low-cost bifunctional catalysts are crucial to energy conversion and storage devices. Herein, a novel oxygen electrode catalyst with high oxygen evolution reaction and oxygen reduction reaction (OER/ORR) performance is reported based on bimetal FeNi nanoparticles anchored on N-doped graphene-like carbon (FeNi/N−C). The complete 2D ultrathin carbon nanosheet is induced by etching and stripping of molten sodium chloride and its ions in the carbonization process at suitable temperature. The obtained FeNi/N−C catalyst exhibits rapid reaction kinetics for OER, efficient four electron transfer for ORR, and outstanding bifunctional performance with reversible oxygen electrode index of 0.87 V for OER/ORR. Zn-air batteries with a high open-circuit voltage of 1.46 V and a stable discharge voltage of 1.23 V are assembled using liquid electrolytes, zinc sheet as Zn-electrode and FeNi/N−C coating on carbon cloth as air-electrode. The specific capacity is as high as 816 mAh g⁻¹ and there is extremely little decay after charge-discharge cycle time of 275 h for the FeNi/N−C as oxygen electrode catalyst in Zn-air battery, which are much better than that assembled with Pt/C−RuO₂ catalyst.     

氧化钌/石墨纳米片复合阵列电极的制备及其电容性能

通过电化学剥离法在石墨棒表面构筑了层数不等、彼此平行且垂直于基底的二维石墨纳米片(GNS)阵列, 而后采用阴极还原电沉积法在GNSs 表面均匀地包覆了一层氧化钌(RuO₂·xH₂O)薄膜, 形成了RuO₂·xH₂O/GNS 复合阵列电极. 电化学测试表明, RuO₂·xH₂O/GNS 复合阵列电极具有优良的超电容性能, 在0.5mol·L^-1 H₂SO₄电解质溶液中, 扫描速率为5 mV·s^-1, 电位窗口为0.9 V时, 其比电容高达4226 F·m^-2, 并且具有优异的循环性能, 经过20000圈充放电循环后, 电容保持率高达94.18%.     

A High Faraday Efficiency NiMoO4 Nanosheet Array Catalyst by Adjusting the Hydrophilicity for Overall Water Splitting

To obtain a highly active, stable, and binder-free electrode based on transition-metal compounds for water splitting, nickel foam-supported 3D NiMoO₄ nanosheet arrays modified with 0D Fe-doped carbon quantum dots (Fe-CQDs/NiMoO₄/NF) are synthesized. The structure characterizations indicated that 0D Fe-CQDs are evenly dispersed onto the NiMoO₄ sheets of the arrays. The contact angle analysis confirmed that the surface hydrophilia of the arrays is improved after the 0D Fe-CQDs are deposited 3D on the NiMoO₄ sheets. Here, both the activity and durability in electrochemical water splitting are significantly enhanced with the Fe-CQDs/NiMoO₄/NF catalysts. At a current density of 10 mA cm⁻², the resultant Fe-CQDs/NiMoO₄/NF revealed an overpotential of only 117 mV for the hydrogen evolution reaction (HER), a relatively low overpotential of 336 mV toward the oxygen evolution reaction (OER), and a Faraday efficiency of up to 99 %. This performance can be attributed to the unique 3D nanosheet array structure, the synergistic effect, and the optimal hydrophilia for gas evolution evolved from the electrode surface.     

Metallic Single‐Unit‐Cell Orthorhombic Cobalt Diselenide Atomic Layers: Robust Water‐Electrolysis Catalysts

The bottleneck in water electrolysis lies in the kinetically sluggish oxygen evolution reaction (OER). Herein, conceptually new metallic non‐metal atomic layers are proposed to overcome this drawback. Metallic single‐unit‐cell CoSe₂ sheets with an orthorhombic phase are synthesized by thermally exfoliating a lamellar CoSe₂‐DETA hybrid. The metallic character of orthorhombic CoSe₂ atomic layers, verified by DFT calculations and temperature‐dependent resistivities, allows fast oxygen evolution kinetics with a lowered overpotential of 0.27 V. The single‐unit‐cell thickness means 66.7 % of the Co²⁺ ions are exposed on the surface and serve as the catalytically active sites. The lowered Co²⁺ coordination number down to 1.3 and 2.6, gives a lower Tafel slope of 64 mV dec^?1 and higher turnover frequency of 745 h^?1. Thus, the single‐unit‐cell CoSe₂ sheets have around 2 and 4.5 times higher catalytic activity compared with the lamellar CoSe₂‐DETA hybrid and bulk CoSe₂.