Synergistic Nanotubular Copper‐Doped Nickel Catalysts for Hydrogen Evolution Reactions

Developing highly active electrocatalysts with low cost and high efficiency for hydrogen evolution reactions (HERs) is of great significance for industrial water electrolysis. Herein, a 3D hierarchically structured nanotubular copper‐doped nickel catalyst on nickel foam (NF) for HER is reported, denoted as Ni(Cu), via facile electrodeposition and selective electrochemical dealloying. The as‐prepared Ni(Cu)/NF electrode holds superlarge electrochemical active surface area and exhibits Pt‐like electrocatalytic activity for HER, displaying an overpotential of merely 27 mV to achieve a current density of 10 mA cm^?2 and an extremely small Tafel slope of 33.3 mV dec^?1 in 1 m KOH solution. The Ni(Cu)/NF electrode also shows excellent durability and robustness in both continuous and intermittent bulk water electrolysis. Density functional theory calculations suggest that Cu substitution and the formation of NiO on the surface leads to more optimal free energy for hydrogen adsorption. The lattice distortion of Ni caused by Cu substitution, the increased interfacial activity induced by surface oxidation of nanoporous Ni, and numerous active sites at Ni atom offered by the 3D hierarchical porous structure, all contribute to the dramatically enhanced catalytic performance. Benefiting from the facile, scalable preparation method, this highly efficient and robust Ni(Cu)/NF electrocatalyst holds great promise for industrial water–alkali electrolysis.     

In Situ Derived Co?B Nanoarray: A High‐Efficiency and Durable 3D Bifunctional Electrocatalyst for Overall Alkaline Water Splitting

The development of efficient bifunctional catalysts for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is of extreme importance for future renewable energy systems. This Communication reports the recent finding that room‐temperature treatment of CoO nanowire array on Ti mesh by NaBH₄ in alkaline media leads to in situ development of Co? B nanoparticles on nanowire surface. The resulting self‐supported Co? B@CoO nanoarray behaves as a 3D bifunctional electrocatalyst with high activity and durability for both HER (<17% current density degradation after 20 h electrolysis) and OER (<14% current density degradation after 20 h electrolysis) with the need of the overpotentials of 102 and 290 mV to drive 50 mA cm^?2 in 1.0 m KOH, respectively. Moreover, its two‐electrode alkaline water electrolyzer also shows remarkably high durability and only demands a cell voltage of 1.67 V to deliver 50 mA cm^?2 water‐splitting current with a current density retention of 81% after 20 h electrolysis. This work provides a promising methodology for the designing and fabricating of metal‐boride based nanoarray as a high‐active water‐splitting catalyst electrode for applications.     

In Situ Derived CoB Nanoarray: A High‐Efficiency and Durable 3D Bifunctional Electrocatalyst for Overall Alkaline Water Splitting

The development of efficient bifunctional catalysts for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is of extreme importance for future renewable energy systems. This Communication reports the recent finding that room‐temperature treatment of CoO nanowire array on Ti mesh by NaBH₄ in alkaline media leads to in situ development of Co?B nanoparticles on nanowire surface. The resulting self‐supported Co?B@CoO nanoarray behaves as a 3D bifunctional electrocatalyst with high activity and durability for both HER (<17% current density degradation after 20 h electrolysis) and OER (<14% current density degradation after 20 h electrolysis) with the need of the overpotentials of 102 and 290 mV to drive 50 mA cm^?2 in 1.0 m KOH, respectively. Moreover, its two‐electrode alkaline water electrolyzer also shows remarkably high durability and only demands a cell voltage of 1.67 V to deliver 50 mA cm^?2 water‐splitting current with a current density retention of 81% after 20 h electrolysis. This work provides a promising methodology for the designing and fabricating of metal‐boride based nanoarray as a high‐active water‐splitting catalyst electrode for applications.     

Self-supporting nanoporous Ni/metallic glass composites with hierarchically porous structure for efficient hydrogen evolution reaction

Searching for free-standing and cost-efficient hydrogen evolution reaction (HER) electrocatalysts with high efficiency and excellent durability remains a great challenge for the hydrogen-based energy industry.Here,we report fabrication of a unique hierarchically porous structure,i.e.,nanoporous Ni (NPN)/metallic glass (MG) composite,through surface dealloying of the specially designed Ni40Zr40Ti20 MG wire.This porous composite is composed of micrometer slits staggered with nanometer pores,which not only enlarges effective surface areas for the catalytic reaction,but also facilitates the release of H2 gas.As a result,the NPN/MG hybrid electrode exhibited the prominent HER performance with a low overpotential of 78 mV at 10 mAcm-2 and Tafel slope of 42.4 mV dec-1,along with outstanding stability in alkaline solutions.Outstanding catalytic properties,combining with their free-standing capability and cost efficiency,make the current composite electrode viable for HER applications.     

3D hierarchical NiS_2/MoS_2 nanostructures on CFP with enhanced electrocatalytic activity for hydrogen evolution reaction

The electrocatalytic activity for hydrogen evolution reaction(HER) is strongly correlated with active edge sites and resulting efficient charge transport capability. Here, we presented a facile two-step method to synthesize 3 D hierarchical NiS_2/MoS_2 composite nanostructures on a carbon fiber paper(CFP) skeleton.The nanostructures distributed on CFP uniformly and composed of 2 D nanosheets, which would provide plenty of active edge sites and increase the HER activity. Electrochemical measurement suggests that the prepared NiS_2/MoS_2 exhibit great HER activity including a low overpotential of 102 m V, a small Tafel slope of 67 m V/dec, and a high double-layer capacity of 53.7 m F/cm~2 in 1 M KOH aqueous solution. In addition,the HER activity is almost unchanged after galvanostatic technique with applied current densities of10 m A/cm~2 for 20 h.     

沉淀法制备氧化镍纳米晶

以Ni(NO3)2和(NH2)2CO3为原料,在水溶液中反应得Ni2(OH)2CO3前驱体,前驱体经400℃热解可得平均粒径为20．3nm无团聚的纳米NiO粉体。经XRD分析可知无Ni、Ni2O3等衍射峰存在,同时将实验结果与乙醇溶液中草酸盐沉淀法及水溶液中NH2HCO3作沉淀剂所得产物进行了比较,并分析了水溶液中(NH2)2CO3沉淀法的优点。     

Transition‐Metal‐Doped RuIr Bifunctional Nanocrystals for Overall Water Splitting in Acidic Environments

The establishment of electrocatalysts with bifunctionality for efficient oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) in acidic environments is necessary for the development of proton exchange membrane (PEM) water electrolyzers for the production of clean hydrogen fuel. RuIr alloy is considered to be a promising electrocatalyst because of its favorable OER performance and potential for HER. Here, the design of a bifunctional electrocatalyst with greatly boosted water‐splitting performance from doping RuIr alloy nanocrystals with transition metals that modify electronic structure and binding strength of reaction intermediates is reported. Significantly, Co‐RuIr results in small overpotentials of 235 mV for OER and 14 mV for HER (@ 10 mA cm^?2 current density) in 0.1 m HClO₄ media. Therefore a cell voltage of just 1.52 V is needed for overall water splitting to produce hydrogen and oxygen. More importantly, for a series of M‐RuIr (M = Co, Ni, Fe), the catalytic activity dependence at fundamental level on the chemical/valence states is used to establish a novel composition‐activity relationship. This permits new design principles for bifunctional electrocatalysts.     

Reduction Kinetics of Nickel Sulphide

Reduction kinetics of Ni_3S_2 was experimen-tally studied by following the time required forcompletion of the hydrogen reduction reaction inthe presence of calcium oxide.A simple empiricalintegration equation,derived for describing the ef-fect of CaO/S molar ratio,temperature,hydrogenconcentration and the average diameter ofNi_3S_2 grains,may be shown as following:t|_(X=1)=2.317×10~(-6)d_(Ni_3S_2) C_(H_2)~(-1)β~(-2.29)e~(13710/T),minThe reduction reaction is of first order with respectto hydrogen concentration,and the apparent reac-tion activation energy is 114.0 kJ/mol.A great ma-jority of metallic Ni reduced from Ni_3S_2 is distrib-uted in the products evenly.     

碳酸盐前躯体Ni_(1/3)Co_(1/3)Mn_(1/3)CO_3合成条件的研究

以碳酸盐为沉淀剂,采用共沉淀法合成Ni1/3Co1/3Mn1/3CO3前驱体,再按照一定的锂配比将其烧结合成层状Li(Ni1/3Co1/3Mn1/3)O2。通过SEM及电性能测试仪等方法研究了碳酸盐前躯体的合成条件,考察了碳酸盐前躯体的振实密度与合成的pH值、溶液浓度以及反应时间的关系。经过实验分析,在pH=8、溶液浓度为2mol·L-1,反应时12～13h时合成的碳酸盐前躯体Ni1/3Co1/3Mn1/3CO3振实密度达到最高值0.98g·cm-3。     

A Robust Nonprecious CuFe Composite as a Highly Efficient Bifunctional Catalyst for Overall Electrochemical Water Splitting

To generate hydrogen, which is a clean energy carrier, a combination of electrolysis and renewable energy sources is desirable. In particular, for both the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) in electrolysis, it is necessary to develop nonprecious, efficient, and durable catalysts. A robust nonprecious copper–iron (CuFe) bimetallic composite is reported that can be used as a highly efficient bifunctional catalyst for overall water splitting in an alkaline medium. The catalyst exhibits outstanding OER and HER activity, and very low OER and HER overpotentials (218 and 158 mV, respectively) are necessary to attain a current density of 10 mA cm^?2. When used in a two‐electrode water electrolyzer system for overall water splitting, it not only achieves high durability (even at a very high current density of 100 mA cm^?2) but also reduces the potential required to split water into oxygen and hydrogen at 10 mA cm^?2 to 1.64 V for 100 h of continuous operation.     

Self-supporting Co0.85Se nanosheets anchored on Co plate as highly efficient electrocatalyst for hydrogen evolution reaction in both acidic and alkaline media

Electrocatalytic water splitting via hydrogen evolution reaction (HER) represents one of promising strategies to gain hydrogen energy. In current work, self-supporting Co_0.85Se nanosheets network anchored on Co plate (Co_0.85Se NSs@Co) is fabricated by employing easily tailorable Co metal plate as the source conductive substrate. The scalable dealloying and hydrothermal selenization strategy was employed to build one layer of three dimensional interlinking Co_0.85Se nanosheets network on the surface of Co plate. Benefiting from bulky integrated architecture and rich active sites, the as-made Co_0.85Se NSs@Co exhibits superior electrocatalytic activity and long-term catalytic durability toward HER. It only requires lower overpotentials of 121 and 162 mV to drive the current density of 10 mA·cm⁻² for hydrogen evolution in 0.5 M H₂SO₄ and 1 M KOH solution. Especially, no evident activity decay occurs upon 1,500 cycles or continuous test for 20 h at 10 mA·cm⁻² in both acidic and alkaline electrolytes. With the merits of exceptional performances, scalable production, and low cost, the self-supporting Co_0.85Se NSs@Co holds prospective application potential as stable and binder-free electrocatalysts for hydrogen generation in a wide range of electrolyte.

     

Transition‐Metal‐Based Electrocatalysts as Cocatalysts for Photoelectrochemical Water Splitting: A Mini Review

Converting solar energy into hydrogen via photoelectrochemical (PEC) water splitting is one of the most promising approaches for a sustainable energy supply. Highly active, cost‐effective, and robust photoelectrodes are undoubtedly crucial for the PEC technology. To achieve this goal, transition‐metal‐based electrocatalysts have been widely used as cocatalysts to improve the performance of PEC cells for water splitting. Herein, this Review summarizes the recent progresses of the design, synthesis, and application of transition‐metal‐based electrocatalysts as cocatalysts for PEC water splitting. Mo, Ni, Co‐based electrocatalysts for the hydrogen evolution reaction (HER) and Co, Ni, Fe‐based electrocatalysts for the oxygen evolution reaction (OER) are emphasized as cocatalysts for efficient PEC HER and OER, respectively. Particularly, some most efficient and robust photoelectrode systems with record photocurrent density or durability for the half reactions of HER and OER are highlighted and discussed. In addition, the self‐biased PEC devices with high solar‐to‐hydrogen efficiency based on earth‐abundant materials are also addressed. Finally, this Review is concluded with a summary and remarks on some challenges and opportunities for the further development of transition‐metal‐based electrocatalysts as cocatalysts for PEC water splitting.     

Ultrathin Ni(0)-Embedded Ni(OH)2 Heterostructured Nanosheets with Enhanced Electrochemical Overall Water Splitting

The efficiency of splitting water into hydrogen and oxygen is highly dependent on the catalyst used. Herein, ultrathin Ni(0)-embedded Ni(OH)₂ heterostructured nanosheets, referred to as Ni/Ni(OH)₂ nanosheets, with superior water splitting activity are synthesized by a partial reduction strategy. This synthetic strategy confers the heterostructured Ni/Ni(OH)₂ nanosheets with abundant Ni(0)-Ni(II) active interfaces for hydrogen evolution reaction (HER) and Ni(II) defects as transitional active sites for oxygen evolution reaction (OER). The obtained Ni/Ni(OH)₂ nanosheets exhibit noble metal-like electrocatalytic activities toward overall water splitting in alkaline condition, to offer 10 mA cm⁻² in HER and OER, the required overpotentials are only 77 and 270 mV, respectively. Based on such an outstanding activity, a water splitting electrolysis cell using the Ni/Ni(OH)₂ nanosheets as the cathode and anode electrocatalysts has been successfully built. When the output voltage of the electrolytic cell is 1.59 V, a current density of 10 mA cm⁻² can be obtained. Moreover, the durability of Ni/Ni(OH)₂ nanosheets in the alkaline electrolyte is much better than that of noble metals. No obvious performance decay is observed after 20 h of catalysis. This facile strategy paves the way for designing highly active non-precious-metal catalyst to generate both hydrogen and oxygen by electrolyzing water at room temperature.     

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.     

Enhanced electrocatalytic activity of Co@N-doped carbon nanotubes by ultrasmall defect-rich TiO<Subscript>2</Subscript> nanoparticles for hydrogen evolution reaction

Despite being technically possible,splitting water to generate hydrogen is practically unfeasible,mainly because of the lack of sustainable and efficient earth-abundant catalysts for the hydrogen-evolution reaction (HER).Herein,we report a durable and highly active electrochemical HER catalyst based on defect-rich TiO2 nanoparticles loaded on Co nanoparticles@N-doped carbon nanotubes (D-TiO2/Co@NCT) synthesized by electrostatic spinning and a subsequent calcining process.The ultrasmall TiO2 nanoparticles are 1.5-2 nm in size and have a defect-rich structure of oxygen vacancies.D-TiO2/Co@NCT exhibits excellent HER catalytic activity in an acidic electrolyte (0.5 M H2SO4),with a low onset potential of-57.5 mV (1 mA·cm-2),a small Tafel slope of 73.5 mV-dec-1,and extraordinary long-term durability.X-ray photoelectron spectroscopy,electron paramagnetic resonance spectroscopy,and theoretical calculations confirm that the Ti3+ defect-rich structure can effectively regulate the catalytic activity for electrochemical water splitting.     

Fe2+‐Doped Layered Double (Ni,Fe) Hydroxides as Efficient Electrocatalysts for Water Splitting and Self‐Powered Electrochemical Systems

Developing nonprecious electrocatalysts with superior activity and durability for electrochemical water splitting is of great interest but challenging due to the large overpotential required above the thermodynamic standard potential of water splitting (1.23 V). Here, in situ growth of Fe²⁺‐doped layered double (Ni, Fe) hydroxide (NiFe(II,III)‐LDH) on nickel foam with well‐defined hexagonal morphology and high crystallinity by a redox reaction between Fe³⁺ and nickel foam under hydrothermal conditions is reported. Benefiting from tuning the local atomic structure by self‐doping Fe²⁺, the NiFe(II,III)‐LDH catalyst with higher amounts of Fe²⁺ exhibits high activity toward oxygen evolution reaction (OER) as well as hydrogen evolution reaction (HER) activity. Moreover, the optimized NiFe(II,III)‐LDH catalyst for OER (O‐NiFe(II,III)‐LDH) and catalyst for HER (H‐NiFe(II,III)‐LDH) show overpotentials of 140 and 113 mV, respectively, at a current density of 10 mA cm^?2 in 1 m KOH aqueous electrolyte. Using the catalysts for overall water splitting in two‐electrode configuration, a low overpotential of just 1.54 V is required at a benchmark current density of 10 mA cm^?2. Furthermore, it is demonstrated that electrolysis of the water device can be drived by a self‐powered system through integrating a triboelectric nanogenerator and battery, showing a promising way to realize self‐powered electrochemical systems.     

Ni-Fe/γ-Al_2O_3乙醇水蒸汽重整制氢催化剂研究

采用沉淀法制备了一系列不同Fe助剂含量的Ni-Fe/γ-Al_2O_3催化剂.采用XRD、TPR、SEM等手段对催化剂进行表征,发现Fe的加入可以有效地置换出NiAl_2O_4尖晶石中的Ni使之以NiO晶体形式存在.同时,降低了催化剂的还原温度,大大减轻催化剂的团聚现象.催化剂性能测试结果表明,15%Ni-10%Fe/γ-Al_2O_3表现出最好的氢气产率和选择性,650℃时分别为4.71%和68.78%.500℃时对15%Ni-10%Fe/γ-Al_2O_3催化剂进行30h稳定性测试,结果表明,整个阶段氢气的选择性在测试时间段内始终保持在65%左右,没有发现乙烯等副产物.     

氢敏元件的种类及半导体薄膜材料在其中的应用

随着氢燃料电池技术在汽车应用中的日益完善,对高性能氢敏元件的需求也更加迫切。本文介绍了采用不同工作原理制备的氢敏元件的种类,着重描述了半导体薄膜材料的工作原理和改性途径,并针对我国目前研究较少的Ga2O3新型薄膜材料进行了较为详细的综合论述。     

Iridium‐Based Multimetallic Porous Hollow Nanocrystals for Efficient Overall‐Water‐Splitting Catalysis

The development of active and durable bifunctional electrocatalysts for overall water splitting is mandatory for renewable energy conversion. This study reports a general method for controllable synthesis of a class of IrM (M = Co, Ni, CoNi) multimetallic porous hollow nanocrystals (PHNCs), through etching Ir‐based, multimetallic, solid nanocrystals using Fe³⁺ ions, as catalysts for boosting overall water splitting. The Ir‐based multimetallic PHNCs show transition‐metal‐dependent bifunctional electrocatalytic activities for both the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in acidic electrolyte, with IrCo and IrCoNi PHNCs being the best for HER and OER, respectively. First‐principles calculations reveal a ligand effect, induced by alloying Ir with 3d transition metals, can weaken the adsorption energy of oxygen intermediates, which is the key to realizing much‐enhanced OER activity. The IrCoNi PHNCs are highly efficient in overall‐water‐splitting catalysis by showing a low cell voltage of only 1.56 V at a current density of 2 mA cm^?2, and only 8 mV of polarization‐curve shift after a 1000‐cycle durability test in 0.5 m H₂SO₄ solution. This work highlights a potentially powerful strategy toward the general synthesis of novel, multimetallic, PHNCs as highly active and durable bifunctional electrocatalysts for high‐performance electrochemical overall‐water‐splitting devices.     

A highly efficient Fe-doped Ni3S2 electrocatalyst for overall water splitting

The development of efficient and stable electrocatalysts with earth-abundant elements for both oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) in the same electrolyte is incontrovertibly vital in water electrolysis. However, their large-scale fabrication remains a great challenge. Here, we report a self-supported electrocatalyst in the form of Fe-doped Ni₃S₂ nanoparticles in-situ grown on three-dimensional (3D) conductive Fe−Ni alloy foam (Fe−Ni₃S₂/AF) by surface-assisted chemical vapor transport (SACVT) method. Homogeneous growth environment and scalability of SACVT method allow Fe−Ni₃S₂ nanoparticles uniformly growing on AF in large-scale. Fe−Ni₃S₂/AF exhibits high activity and durability when act as HER catalyst and OER precatalyst in alkaline media. The HER and OER overpotential at 10 mA/cm² is considerably small, only 75 and 267 mV, respectively. Moreover, the electrolyzer assembled by Fe−Ni₃S₂/AF for overall water splitting exhibits a low cell voltage and high durability in long-term test. Based on experiments and theoretical calculation, the significantly enhanced activity could be originated from the incorporation of Fe, which contributed to increase the electrochemical active surface area, enhance electrical conductivity, optimize the hydrogen and H₂O adsorption energy of Ni₃S₂ (101) surface in HER, and form active bimetallic Ni−Fe(oxy)hydroxide in OER. The excellent durability of self-supported Fe−Ni₃S₂/AF could be benefited from the in-situ growth of Fe−Ni₃S₂ nanoparticles on 3D AF, which could ensure closely mechanical adhesion between active materials and substrate, promote charge transport and increase surface area. This work provides a facile method for large-scale synthesis of electrocatalysts with high activity and long-term durability for efficient water electrolysis in alkaline media.