High-Performance Bismuth-Doped Nickel Aerogel Electrocatalyst for the Methanol Oxidation Reaction

Low-cost, non-noble-metal electrocatalysts are required for direct methanol fuel cells, but their development has been hindered by limited activity, high onset potential, low conductivity, and poor durability. A surface electronic structure tuning strategy is presented, which involves doping of a foreign oxophilic post-transition metal onto transition metal aerogels to achieve a non-noble-metal aerogel Ni₉₇Bi₃ with unprecedented electrocatalytic activity and durability in methanol oxidation. Trace amounts of Bi are atomically dispersed on the surface of the Ni₉₇Bi₃ aerogel, which leads to an optimum shift of the d-band center of Ni, large compressive strain of Bi, and greatly increased conductivity of the aerogel. The electrocatalyst is endowed with abundant active sites, efficient electron and mass transfer, resistance to CO poisoning, and outstanding performance in methanol oxidation. This work sheds light on the design of high-performance non-noble-metal electrocatalysts.     

Energy‐Saving Electrolytic Hydrogen Generation: Ni2P Nanoarray as a High‐Performance Non‐Noble‐Metal Electrocatalyst

It is highly attractive but challenging to develop earth‐abundant electrocatalysts for energy‐saving electrolytic hydrogen generation. Herein, we report that Ni₂P nanoarrays grown in situ on nickel foam (Ni₂P/NF) behave as a durable high‐performance non‐noble‐metal electrocatalyst for hydrazine oxidation reaction (HzOR) in alkaline media. The replacement of the sluggish anodic oxygen evolution reaction with such the more thermodynamically favorable HzOR enables energy‐saving electrochemical hydrogen production with the use of Ni₂P/NF as a bifunctional catalyst for anodic HzOR and cathodic hydrogen evolution reaction. When operated at room temperature, this two‐electrode electrolytic system drives 500 mA cm⁻² at a cell voltage as low as 1.0 V with strong long‐term electrochemical durability and 100 % Faradaic efficiency for hydrogen evolution in 1.0 m KOH aqueous solution with 0.5 m hydrazine.     

Bottom‐Up Fabrication of a Sandwich‐Like Carbon/Graphene Heterostructure with Built‐In FeNC Dopants as Non‐Noble Electrocatalyst for Oxygen Reduction Reaction

High‐performance non‐noble electrocatalysts for oxygen reduction reaction (ORR) are the prerequisite for large‐scale utilization of fuel cells. Herein, a type of sandwiched‐like non‐noble electrocatalyst with highly dispersed FeN_x active sites embedded in a hierarchically porous carbon/graphene heterostructure was fabricated using a bottom‐up strategy. The in situ ion substitution of Fe³⁺ in a nitrogen‐containing MOF (ZIF‐8) allows the Fe‐heteroatoms to be uniformly distributed in the MOF precursor, and the assembly of Fe‐doped ZIF‐8 nano‐crystals with graphene‐oxide and in situ reduction of graphene‐oxide afford a sandwiched‐like Fe‐doped ZIF‐8/graphene heterostructure. This type of heterostructure enables simultaneous optimization of FeN_x active sites, architecture and interface properties for obtaining an electron‐catalyst after a one‐step carbonization. The synergistic effect of these factors render the resulting catalysts with excellent ORR activities. The half‐wave potential of 0.88 V vs. RHE outperforms most of the none‐noble metal catalyst and is comparable with the commercial Pt/C (20 wt %) catalyst. Apart from the high activity, this catalyst exhibits excellent durability and good methanol‐tolerance. Detailed investigations demonstrate that a moderate content of Fe dopants can effectively increase the intrinsic activities, and the hybridization of graphene can enhance the reaction kinetics of ORR. The strategy proposed in this work gives an inspiration towards developing efficient noble‐metal‐free electrocatalysts for ORR.     

Carbon‐Nanoplated CoS@TiO2 Nanofibrous Membrane: An Interface‐Engineered Heterojunction for High‐Efficiency Electrocatalytic Nitrogen Reduction

Developing noble‐metal‐free electrocatalysts is important to industrially viable ammonia synthesis through the nitrogen reduction reaction (NRR). However, the present transition‐metal electrocatalysts still suffer from low activity and Faradaic efficiency due to poor interfacial reaction kinetics. Herein, an interface‐engineered heterojunction, composed of CoS nanosheets anchored on a TiO₂ nanofibrous membrane, is developed. The TiO₂ nanofibrous membrane can uniformly confine the CoS nanosheets against agglomeration, and contribute substantially to the NRR performance. The intimate coupling between CoS and TiO₂ enables easy charge transfer, resulting in fast reaction kinetics at the heterointerface. The conductivity and structural integrity of the heterojunction are further enhanced by carbon nanoplating. The resulting C@CoS@TiO₂ electrocatalyst achieves a high ammonia yield (8.09×10^?10 mol s^?1 cm^?2) and Faradaic efficiency (28.6 %), as well as long‐term durability.     

Function‐Led Design of Aerogels: Self‐Assembly of Alloyed PdNi Hollow Nanospheres for Efficient Electrocatalysis

One plausible approach to endow aerogels with specific properties while preserving their other attributes is to fine‐tune the building blocks. However, the preparation of metallic aerogels with designated properties, for example catalytically beneficial morphologies and transition‐metal doping, still remains a challenge. Here, we report on the first aerogel electrocatalyst composed entirely of alloyed PdNi hollow nanospheres (HNSs) with controllable chemical composition and shell thickness. The combination of transition‐metal doping, hollow building blocks, and the three‐dimensional network structure make the PdNi HNS aerogels promising electrocatalysts for ethanol oxidation. The mass activity of the Pd₈₃Ni₁₇ HNS aerogel is 5.6‐fold higher than that of the commercial Pd/C catalyst. This work expands the exploitation of the electrocatalysis properties of aerogels through the morphology and composition control of its building blocks.     

Modular Design of Noble‐Metal‐Free Mixed Metal Oxide Electrocatalysts for Complete Water Splitting

Electrocatalytic water splitting into H₂ and O₂ is a key technology for carbon‐neutral energy. Here, we report a modular materials design leading to noble metal‐free composite electrocatalysts, which combine high electrical conductivity, high OER and HER reactivity and high durability. The scalable bottom‐up fabrication allows the stable deposition of mixed metal oxide nanostructures with different functionalities on copper foam electrodes. The composite catalyst shows sustained OER and HER activity in 0.1 m aqueous KOH over prolonged periods (t>10 h) at low overpotentials (OER: ≈300 mV; HER: ≈100 mV) and high faradaic efficiencies (OER: ≈100 %, HER: ≈98 %). The new synthetic concept will enable the development of multifunctional, mixed metal oxide composites as high‐performance electrocatalysts for challenging energy conversion and storage reactions.     

Electrochemical Oxidation of 5‐Hydroxymethylfurfural on Nickel Nitride/Carbon Nanosheets: Reaction Pathway Determined by In Situ Sum Frequency Generation Vibrational Spectroscopy

2,5‐Furandicarboxylic acid was obtained from the electrooxidation of 5‐hydroxymethylfurfural (HMF) with non‐noble metal‐based catalysts. Moreover, combining the biomass oxidation with the hydrogen evolution reaction (HER) increased the energy conversion efficiency of an electrolyzer and also generated value‐added products at both electrodes. Here, the reaction pathway on the surface of a carbon‐coupled nickel nitride nanosheet (Ni₃N@C) electrode was evaluated by surface‐selective vibrational spectroscopy using sum frequency generation (SFG) during the electrochemical oxidation. The Ni₃N@C electrode shows catalytic activities for HMF oxidation and the HER. As the first in situ SFG study on transition‐metal nitride for the electrooxidation upgrade of HMF, this work not only demonstrates that the reaction pathway of electrochemical oxidation but also provides an opportunity for nonprecious metal nitrides to simultaneously upgrade biomass and produce H₂ under ambient conditions.     

Stability and Activity of Non‐Noble‐Metal‐Based Catalysts Toward the Hydrogen Evolution Reaction

A fundamental understanding of the behavior of non‐noble based materials toward the hydrogen evolution reaction is crucial for the successful implementation into practical devices. Through the implementation of a highly sensitive inductively coupled plasma mass spectrometer coupled to a scanning flow cell, the activity and stability of non‐noble electrocatalysts is presented. The studied catalysts comprise a range of compositions, including metal carbides (WC), sulfides (MoS₂), phosphides (Ni₅P₄, Co₂P), and their base metals (W, Ni, Mo, Co); their activity, stability, and degradation behavior was elaborated and compared to the state‐of‐the‐art catalyst platinum. The non‐noble materials are stable at HER potentials but dissolve substantially when no current is flowing. Through pre‐ and post‐characterization of the catalysts, explanations of their stability (thermodynamics and kinetics) are discussed, challenges for the application in real devices are analyzed, and strategies for circumventing dissolution are suggested. The precise correlation of metal dissolution with applied potential/current density allows for narrowing down suitable material choices as replacement for precious group metals as for example, platinum and opens up new ways in finding cost‐efficient, active, and stable new‐generation electrocatalysts.     

Titanium Dioxide‐Grafted Copper Complexes: High‐Performance Electrocatalysts for the Oxygen Reduction Reaction in Alkaline Media

The sluggish kinetics of the oxygen reduction reaction (ORR) at the cathodes of fuel cells significantly hampers fuel cell performance. Therefore, the development of high‐performance, non‐precious‐metal catalysts as alternatives to noble metal Pt‐based ORR electrocatalysts is highly desirable for the large‐scale commercialization of fuel cells. TiO₂‐grafted copper complexes deposited on multiwalled carbon nanotubes (CNTs) form stable and efficient electrocatalysts for the ORR. The optimized catalyst composite CNTs@TiO₂–ZA–[Cu(phen)(BTC)] shows surprisingly high selectivity for the 4 e^? reduction of O₂ to water (approximately 97 %) in alkaline solution with an onset potential of 0.988 V vs. RHE, and demonstrates superior stability and excellent tolerance for the methanol crossover effect in comparison to a commercial Pt/C catalyst. The copper complexes were grafted onto the surface of TiO₂ through coordination of an imidazole‐containing ligand, zoledronic acid (ZA), which binds to TiO₂ through its bis‐phosphoric acid anchoring group. Rational optimization of the copper catalyst’s ORR performance was achieved by using an electron‐deficient ligand, 5‐nitro‐1,10‐phenanthroline (phen), and bridging benzene‐1,3,5‐tricarboxylate (BTC). This facile approach to the assembly of copper catalysts on TiO₂ with rationally tuned ORR activity will have significant implications for the development of high‐performance, non‐precious‐metal ORR catalysts.     

Controlled Synthesis of 3D Flower‐like Ni2P Composed of Mesoporous Nanoplates for Overall Water Splitting

Developing efficient non‐noble metal and earth‐abundant electrocatalysts with tunable microstructures for overall water splitting is critical to promote clean energy technologies for a hydrogen economy. Herein, novel three‐dimensional (3D) flower‐like Ni₂P composed of mesoporous nanoplates with controllable morphology and high surface area was prepared by a hydrothermal method and low‐temperature phosphidation as efficient electrocatalysts for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Compared with the urchin‐like Ni_x P_y , the 3D flower‐like Ni₂P with a diameter of 5 μm presented an efficient and stable catalytic performance in 0.5 m H₂SO₄, with a small Tafel slope of 79 mV dec⁻¹ and an overpotential of about 240 mV at a current density of 10 mA cm⁻² with a mass loading density of 0.283 mg cm⁻². In addition, the catalyst also exhibited a remarkable performance for the OER in 1.0 m KOH electrolyte, with an overpotential of 320 mV to reach a current density of 10 mA cm⁻² and a small Tafel slope of 72 mV dec⁻¹. The excellent catalytic performance of the as‐prepared Ni₂P may be ascribed to its novel 3D morphology with unique mesoporous structure.     

Synthesis of Highly Active and Stable Spinel‐Type Oxygen Evolution Electrocatalysts by a Rapid Inorganic Self‐Templating Method

Composition‐adjustable spinel‐type metal oxides, Mn_xCo_3?xO_4?δ (x=0.8–1.4), were synthesized in ethanol solutions by a rapid inorganic self‐templating mechanism using KCl nanocrystals as the structure‐directing agent. The Mn_xCo_3?xO_4?δ materials showed ultrahigh oxygen evolution activity and strong durability in alkaline solutions, and are capable of delivering a current density of 10 mA cm^?2 at 1.58 V versus the reversible hydrogen electrode in 0.1 M KOH solution, which is superior in comparison to IrO₂ catalysts under identical experimental conditions, and comparable to the most active noble‐metal and transition‐metal oxygen evolution electrocatalysts reported so far. The high performance for catalytic oxygen evolution originates from both compositional and structural features of the synthesized materials. The moderate content of Mn doping into the spinel framework led to their improved electronic conductivity and strong oxidizing ability, and the well‐developed porosity, accompanied with the high affinity between OH^? reactants and catalyst surface, contributed to the smooth mass transport, thus endowing them with superior oxygen evolution activity.     

CoP‐Doped MOF‐Based Electrocatalyst for pH‐Universal Hydrogen Evolution Reaction

Although electrocatalysts based on transition metal phosphides (TMPs) with cationic/anionic doping have been widely studied for hydrogen evolution reaction (HER), the origin of performance enhancement still remains elusive mainly due to the random dispersion of dopants. Herein, we report a controllable partial phosphorization strategy to generate CoP species within the Co‐based metal‐organic framework (Co‐MOF). Density functional theory calculations and experimental results reveal that the electron transfer from CoP to Co‐MOF through N‐P/N‐Co bonds could lead to the optimized adsorption energy of H₂O (ΔG ) and hydrogen (ΔG_H*), which, together with the unique porous structure of Co‐MOF, contributes to the remarkable HER performance with an overpotential of 49 mV at a current density of 10 mA cm^?2 in 1 m phosphate buffer solution (PBS, pH 7.0). The excellent catalytic performance exceeds almost all the documented TMP‐based and non‐noble‐metal‐based electrocatalysts. In addition, the CoP/Co‐MOF hybrid also displays Pt‐like performance in 0.5 m H₂SO₄ and 1 m KOH, with the overpotentials of 27 and 34 mV, respectively, at a current density of 10 mA cm^?2.     

Facile Synthesis of PdCu Echinus‐Like Nanocrystals as Robust Electrocatalysts for Methanol Oxidation Reaction

Exploiting high‐performance and inexpensive electrocatalysts for methanol electro‐oxidation is conductive to promoting the commercial application of direct methanol fuel cells. Here, we present a facile synthesis of echinus‐like PdCu nanocrystals (NCs) via a one‐step and template‐free method. The echinus‐like PdCu NCs possess numerous straight and long branches which can provide abundant catalytic active sites. Owing to the novel nanoarchitecture and electronic effect of the PdCu alloy, the echinus‐like PdCu NCs display high electrocatalytic performance toward methanol oxidation reaction in an alkaline medium. The mass activity of echinus‐like PdCu NCs is 1202.1 mA mg_Pd^?1, which is 3.7 times that of Pd/C catalysts. In addition, the echinus‐like structure, as a kind of three‐dimensional self‐supported nanoarchitecture, endows PdCu NCs with significantly enhanced stability and durability. Hence, the echinus‐like PdCu NCs hold prospect of being employed as electrocatalysts for direct alcohol fuel cells.     

Molybdenum‐tungsten Oxide Nanowires Rich in Oxygen Vacancies as An Advanced Electrocatalyst for Hydrogen Evolution

Electrolysis of water is a promising way to produce hydrogen fuel in large scale. The commercialization of this technology requires highly efficient non‐noble metal electrocatalysts to decease the energy input for the hydrogen evolution reaction (HER). In this work, a novel nanowire structured molybdenum‐tungsten bimetallic oxide (CTAB‐D‐W₄MoO₃) is synthesized by a simple hydrothermal method followed with post annealing treatment. The obtained metal oxides feature with enhanced conductivity, rich oxygen vacancies and customized electronic structure. As such, the composite electrocatalyst exhibits excellent electrocatalytic performance for HER in an acidic environment, achieving a large current density of 100 mA cm^?2 at overpotential of only 286 mV and a small Tafel slope of 71.2 mV dec^?1. The excellent electrocatalytic HER performance of CTAB‐D‐W₄MoO₃ is attributed to the unique nanowire structure, rich catalytic active sites and promoted electron transfer rate.     

Boosting Hydrogen Oxidation Activity of Ni in Alkaline Media through Oxygen‐Vacancy‐Rich CeO2/Ni Heterostructures

The search for highly efficient platinum group metal (PGM)‐free electrocatalysts for the hydrogen oxidation reaction (HOR) in alkaline electrolytes remains a great challenge in the development of alkaline exchange membrane fuel cells (AEMFCs). Here we report the synthesis of an oxygen‐vacancy‐rich CeO₂/Ni heterostructure and its remarkable HOR performance in alkaline media. Experimental results and density functional theory (DFT) calculations indicate the electron transfer between CeO₂ and Ni could lead to thermoneutral adsorption free energies of H* (ΔG_H*). This, together with the promoted OH* adsorption strength derived from the abundance of oxygen vacancies in the CeO₂ species, contributes to the excellent HOR performance with the exchange current density and mass activity of 0.038 mA cm_Ni^?2 and 12.28 mA mg_Ni^?1, respectively. This presents a new benchmark for PGM‐free alkaline HOR and opens a new avenue toward the rational design of high‐performance PGM‐free electrocatalysts for alkaline HOR.     

Single‐Crystalline Ultrathin Nickel Nanosheets Array from In Situ Topotactic Reduction for Active and Stable Electrocatalysis

Simultaneously synthesizing and structuring atomically thick or ultrathin 2D non‐precious metal nanocrystal may offer a new class of materials to replace the state‐of‐art noble‐metal electrocatalysts; however, the synthetic strategy is the bottleneck which should be urgently solved. Here we report the synthesis of an ultrathin nickel nanosheet array (Ni‐NSA) through in situ topotactic reduction from Ni(OH)₂ array precursors. The Ni nanosheets showed a single‐crystalline lamellar structure with only ten atomic layers in thickness and an exposed (111) facet. Combined with a superaerophobic (low bubble adhesive) arrayed structure the Ni‐NSAs exhibited a dramatic enhancement on both activity and stability towards the hydrazine‐oxidation reaction (HzOR) relative to platinum. Furthermore, the partial oxidization of Ni‐NSAs in ambient atmosphere resulted in effective water‐splitting electrocatalysts for the hydrogen‐evolution reaction (HER).     

Identification of Key Reversible Intermediates in Self‐Reconstructed Nickel‐Based Hybrid Electrocatalysts for Oxygen Evolution

The oxygen evolution reaction (OER) has been explored extensively for reliable hydrogen supply to boost the energy conversion efficiency. The superior OER performance of newly developed non‐noble metal electrocatalysts has concealed the identification of the real active species of the catalysts. Now, the critical active phase in nickel‐based materials (represented by NiNPS) was directly identified by observing the dynamic surface reconstruction during the harsh OER process via combining in situ Raman tracking and ex situ microscopy and spectroscopy analyses. The irreversible phase transformation from NiNPS to α‐Ni(OH)₂ and reversible phase transition between α‐Ni(OH)₂ and γ‐NiOOH prior to OER demonstrate γ‐NiOOH as the key active species for OER. The hybrid catalyst exhibits 48‐fold enhanced catalytic current at 300 mV and remarkably reduced Tafel slope to 46 mV dec^?1, indicating the greatly accelerated catalytic kinetics after surface evolution.     

Tailoring Transition‐Metal Hydroxides and Oxides by Photon‐Induced Reactions

Controlled synthesis of transition‐metal hydroxides and oxides with earth‐abundant elements have attracted significant interest because of their wide applications, for example as battery electrode materials or electrocatalysts for fuel generation. Here, we report the tuning of the structure of transition‐metal hydroxides and oxides by controlling chemical reactions using an unfocused laser to irradiate the precursor solution. A Nd:YAG laser with wavelengths of 532 nm or 1064 nm was used. The Ni²⁺, Mn²⁺, and Co²⁺ ion‐containing aqueous solution undergoes photo‐induced reactions and produces hollow metal‐oxide nanospheres (Ni_0.18Mn_0.45Co_0.37O_x) or core–shell metal hydroxide nanoflowers ([Ni_0.15Mn_0.15Co_0.7(OH)₂](NO₃)_0.2?H₂O), depending on the laser wavelengths. We propose two reaction pathways, either by photo‐induced redox reaction or hydrolysis reaction, which are responsible for the formation of distinct nanostructures. The study of photon‐induced materials growth shines light on the rational design of complex nanostructures with advanced functionalities.     

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.     

新型的钛基Ni-Sn/Ti电极的制备及对甲醇氧化反应的电催化活性

利用电热法,一步制备出新型的钛基Ni-Sn/Ti电极(Ni8Sn/Ti, Ni7Sn3/Ti 和 Ni/Ti)。扫描电镜（SEM）图像表明,催化剂以片状的纳米颗粒形式沉积于钛基体上。利用电化学伏安技术、电位阶跃法和电化学交流阻抗谱（EIS）,研究了这些电极在1mol.L�1NaOH溶液中对甲醇氧化反应的电催化活性。研究表明,与Ni7Sn3/Ti,Ni/Ti以及多晶镍电极相比,Ni8Sn/Ti电极对甲醇氧化反应表现出更高的阳极氧化电流和更低的起始电位。EIS分析表明,在本文所考察的阳极电位和甲醇浓度下,Ni8Sn/Ti电极对甲醇氧化反应显示出极低的电荷传递电阻。结果表明,这种新型的钛基Ni8Sn/Ti电极对甲醇氧化反应具有极高的电催化活性。