Hierarchically wood-derived integrated electrode with tunable superhydrophilic/superaerophobic surface for efficient urea electrolysis

Conferring surfaces with superhydrophilic/superaerophobic characteristics is desirable for synthesizing efficient gas reaction catalysts.However,complicated procedures,high costs,and poor interfaces hinder commercialization.Here,an integrated electrode with tunable wettability derived from a hierarchically porous wood scaffold was well designed for urea oxidation reaction(UOR).Interestingly,the outer surface of the wood lumen was optimized to the preferred wettability via stoichiometry to promote electrolyte permeation and gas escape.This catalyst exhibits outstanding activity and durability for UOR in alkaline media,requiring only a potential of 1.36 V(vs.RHE)to deliver 10 m A cm^(-2)and maintain its activity without significant decay for 60 h.These experiments and theoretical calculations demonstrate that the nickel(oxy)hydroxide layer formed through surface reconstruction of nickel nanoparticles improves the active sites and intrinsic activity.Moreover,the superwetting properties of the electrode promote mass transfer by guaranteeing substantial contact with the electrolyte and accelerating the separation of gaseous products during electrocatalysis.These findings provide the understanding needed to manipulate the surface wettability through rational design and fabrication of efficient electrocatalysts for gas-evolving processes.

Ambient Fast Synthesis of Superaerophobic/Superhydrophilic Electrode for Superior Electrocatalytic Water Oxidation

Developing cost-effective and facile methods to synthesize efficient and stable electrocatalysts for large-scale water splitting is highly desirable but remains a significant challenge.In this study,a facile ambient temperature synthesis of hierarchical nickel-iron(oxy)hydroxides nanosheets on iron foam(FF-FN)with both superhydrophilicity and superaerophobicity is reported.Specifically,the as-fabricated FF-FN electrode demonstrates extraordinary oxygen evolution reaction(OER)activity with an ultralow overpotential of 195 mV at 10 mA cm^(-2)and a small Tafel slope of 34 mV dec^(-1)in alkaline media.Further theoretical investigation indicates that the involved lattice oxygen in nickel-iron-based-oxyhydroxide during electrochemical self-reconstruction can significantly reduce the OER reaction overpotential via the dominated lattice oxygen mechanism.The rechargeable Zn-air battery assembled by directly using the as-prepared FF-FN as cathode displays remarkable cycling performance.It is believed that this work affords an economical approach to steer commercial Fe foam into robust electrocatalysts for sustainable energy conversion and storage systems.

Aluminum and phosphorus codoped “superaerophobic” Co3O4 microspheres for highly efficient electrochemical water splitting and Zn-air batteries

Multifunctional non-precious catalysts for hydrogen/oxygen evolution reaction(HER/OER) and oxygen reduction reaction(ORR) constitute the bottleneck in the applications in electrochemical overall water splitting(OWS) and Zn-air batteries. Herein, a trifunctional electrocatalyst of urchin-like Al,P-codoped Co3O4 microspheres supported on Ni foam(denoted as AP-CONPs/NF) was fabricated via a hydrothermal process and subsequent low-temperature annealing and phosphorization, exhibiting enhanced OER, HER and ORR activities compared with single-doped and undoped samples. Their surface self-organized microstructure and excellent "superaerophobic" feature make a high bubble repellency, which boost diffusion of reactants and electrolyte-electrode intimate contact. The codoping of Al and P elements into Co3O4 betters right the balance among surface chemical state, the increased oxygen vacancies and the promoted charge transfer. Encouraged by these synergistic advantages, the AP-CONPs/NF was further employed as excellent bifunctional electrodes for the OWS(low cell voltage of 1.57 V at 10 mA cm-2) and as air cathode for rechargeable Zn-air batteries(high power density of 89.1 mW cm-2), which demonstrates a great feasibility for practical applications.

A Superaerophobic Bimetallic Selenides Heterostructure for Efficient Industrial-Level Oxygen Evolution at Ultra-High Current Densities

Cost-effective and stable electrocatalysts with ultra-high current densities for electrochemical oxygen evolution reaction(OER)are critical to the energy crisis and environmental pollution.Herein,we report a superaerophobic three dimensional(3D)heterostructured nanowrinkles of bimetallic selenides consisting of crystalline NiSe2 and NiFe2Se4 grown on NiFe alloy(NiSe2/NiFe2Se4@NiFe)prepared by a thermal selenization procedure.In this unique 3D heterostructure,numerous nanowrinkles of NiSe2/NiFe2Se4 hybrid with a thickness of ~100 nm are grown on NiFe alloy in a uniform manner.Profiting by the large active surface area and high electronic conductivity,the superaerophobic NiSe2/NiFe2Se4@NiFe heterostructure exhibits excellent electrocatalytic activity and durability towards OER in alkaline media,outputting the low potentials of 1.53 and 1.54 V to achieve ultra-high current densities of 500 and 1000 mA cm^−2,respectively,which is among the most active Ni/Fe-based selenides,and even superior to the benchmark Ir/C catalyst.The in-situ derived FeOOH and NiOOH species from NiSe2/NiFe2Se4@NiFe are deemed to be efficient active sites for OER.

Biomimetic three-dimensional multilevel nanoarray electrodes with superaerophobicity as efficient bifunctional catalysts for electrochemical water splitting

The design and preparation of cost-effective and durable catalysts for electrochemical water splitting are significant for the development and application of hydrogen production.Herein,inspired by the underwater superaerophobicity of fish scales,a three-dimensional multilevel nanoarray electrode with superaerophobicity was designed and fabricated by the hydrothermal method to solve the bubble shielding effect in electrochemical reactions.Benefiting from the high specific surface area,superaerophobic properties,Al doping,the Al-CoS_(2)nanosheets(NSs)/nickel foam(NF)-30 exhibits outstanding electrocatalytic activity and superior durability for electrochemical water splitting in 1 M KOH.Significantly,the Al-CoS_(2)NSs/NF-30 only required extremely low overpotential of 176 mV for oxygen evolution reaction(OER)to reach a current density of 10 mA·cm^(-2).Al-CoS_(2)NSs/NF-30 was employed as bifunctional electrode for electrochemical water splitting with a cell voltage of 1.58 V at 10 mA·cm^(-2).Meanwhile,Al-CoS_(2) NSs/NF-30 exhibited excellent durability(250 h@10 mA·cm^(-2)and 50 h@100 mA·cm^(-2)).The cobalt-based catalyst(Al-CoS_(2) NSs/NF-30)with superaerophobicity exhibits excellent performance in activity and durability,therefore is a promising electrochemical water splitting catalyst.

Nanovilli electrode boosts hydrogen evolution:A surface with superaerophobicity and superhydrophilicity

Although tremendous efforts have been paid on electrocatalysts toward efficient electrochemical hydrogen generation,breakthrough is still highly needed in the design and synthesis of wonderful non-precious-metal electrocatalyst.Herein,a nanovilli Ni2P electrode,which with superaerophobic and superhydropholic can significantly facilitate the mass and electron transfer was constructed via a facial morphology control strategy.Meanwhile,the substitution of sluggish oxygen evolution with urea oxidation,lowering the two-electrode cell voltage to only 1.48 volts to achieve a current density of 10 mA·cm^(-2).Thus,the as-constructed electrode achieves the operation of hydrogen generation by an AA battery.This work sheds new light on the exploration of other high-efficient electrocatalysts for hydrogen generation by using intermittent clean energy.

富含氧空位的NiFe氢氧化物衍生的具有超疏气纳米阵列形貌的磷化物及其全解水性能

对高效催化剂进行多尺度调控可优化中间体的吸附能量(原子层面),并实现快速传质(三维宏观层面),这对于提升整体水分解性能至关重要.在本工作中,我们首先在镍铁氢氧化物中引入氧空位,然后通过磷化反应将其转化为具有纳米阵列形态的NiFe-Vo-P催化剂.在析氧反应催化过程中,NiFe-Vo-P表面会原位形成磷酸盐阴离子及具有催化活性的Ni(Fe)OOH,能显著优化反应中间体的吸附强度.结果表明,NiFeVo-P在过电位为289 mV时电流密度可达1.5 A cm^(-2).同时,其超亲水/超疏气纳米阵列形貌可有效促进传质,在25和70℃的条件下,可在~2.0V的电池电压下分别获得580 mA cm^(-2)和1.0 A cm^(-2)的电流密度,是未进行超疏气形貌工程催化剂的电流密度的2倍以上.

Ternary NiCoP nanosheet arrays： An excellent bifunctional catalyst for alkaline overall water splitting

Exploring bifunctional catalysts for the hydrogen and oxygen evolution reactions （HER and OER） with high efficiency, low cost, and easy integration is extremely crucial for future renewable energy systems. Herein, ternary NiCoP nanosheet arrays （NSAs） were fabricated on 3D Ni foam by a facile hydrothermal method followed by phosphorization. These arrays serve as bifunctional alkaline catalysts, exhibiting excellent electrocatalytic performance and good working stability for both the HER and OER. The overpotentials of the NiCoP NSA electrode required to drive a current density of 50 mA/cm2 for the HER and OER are as low as 133 and 308 mV, respectively, which is ascribed to excellent intrinsic electrocatalytic activity, fast electron transport, and a unique superaerophobic structure. When NiCoP was integrated as both anodic and cathodic material, the electrolyzer required a potential as low as -1.77 V to drive a current density of 50 mA/cm2 for overall water splitting, which is much smaller than a reported electrolyzer using the same kind of phosphide-based material and is even better than the combination of Pt/C and Ir/C, the best known noble metal-based electrodes. Combining satisfactory working stability and high activity, this NiCoP electrode paves the way for exploring overall water splitting catalysts.

Enhancing oxygen evolution reaction by cationic surfactants

Oxygen evolution reaction is critical for water splitting or metal-air batteries,but previous research mainly focuses on electrode material or structure optimization.Herein,we demonstrate that surfactant modification of a NiFe layered double hydroxide (LDH) array electrode,one of the best catalysts for oxygen evolution reaction (OER),could achieve superaerophobic surface with balanced surface charges,affording fast mass transfer,quick gas release,and boosted OER performance.The assembled surfactants on the electrode surface are responsible for lowering the bubble adhesive force (~ 1.03 μN) and corresponding fast release of small bubbles generated during OER.In addition,the bipolar nature of the hexadecyl trimethyl ammonium bromide (CTAB) molecule lead to bilayer assembly of the surfactants with the polar ends facing the electrode surface and the electrolyte,resulting in neutralized charges on the electrode surface.As a result,OH-transfer was facilitated and OER performance was enhanced.With the modified superaerophobic surface and balanced surface charge,NiFe LDHs-CTAB nanostructured electrode showed ultrahigh current density increase (9.39 mA(mV·cm^2)),2.3 times higher than that for conventional NiFe LDH nanoarray electrode),dramatically fast gas release,and excellent durability.The introduction of surfactants to construct under-water superaerophobic electrode with in-time repelling ability to the as-formed gas bubbles may open up a new pathway for designing efficient electrodes for gas evolution systems with potentially practical application in the near future.

Femtosecond laser micro-nano processing for boosting bubble releasing of gas evolution reactions

Coupling effect of chemical composition and physical structure is a key factor to construct superaerophobic electrodes.Almost all reports about superaerophobic electrodes were aimed at precisely controlling morphology of loaded materials(constructing specific structure)and ignored the due role of substrate.Nevertheless,in this work,by using high precision and controllable femtosecond laser,hierarchical micro-nano structures with superaerophobic properties were constructed on the surface of silicon substrate(fs-Si),and such special super-wettability could be successfully inherited to subsequent self-supporting electrodes through chemical synthesis.Femtosecond laser processing endowed electrodes with high electrochemical surface area,strong physical structure,and remarkable superaerophobic efficacy.As an unconventional processing method,the reconstructed morphology of substrate surface bears the responsibility of superaerophobicity,thus liberating the structural constraints on loaded materials.Since this key of coupling effect is transferred from the loaded materials to substrate,we provided a new general scheme for synthesizing superaerophobic electrodes.The successful introduction of femtosecond laser will open a new idea to synthesize self-supporting electrodes for gas-involving reactions.