Phosphorus‐Modified Tungsten Nitride/Reduced Graphene Oxide as a High‐Performance,Non‐Noble‐Metal Electrocatalyst for the Hydrogen Evolution Reaction

Phosphorus‐modified tungsten nitride/reduced graphene oxide (P‐WN/rGO) is designed as a high‐efficient, low‐cost electrocatalyst for the hydrogen evolution reaction (HER). WN (ca. 3 nm in size) on rGO is first synthesized by using the H₃[PO₄(W₃O₉)₄] cluster as a W source. Followed by phosphorization, the particle size increase slightly to about 4 nm with a P content of 2.52 at %. The interaction of P with rGO and WN results in an obvious increase of work function, being close to Pt metal. The P‐WN/rGO exhibits low onset overpotential of 46 mV, Tafel slope of 54 mV dec⁻¹, and a large exchange current density of 0.35 mA cm⁻² in acid media. It requires overpotential of only 85 mV at current density of 10 mA cm⁻², while remaining good stability in accelerated durability testing. This work shows that the modification with a second anion is powerful way to design new catalysts for HER.     

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.     

Donor–Acceptor Nanocarbon Ensembles to Boost Metal‐Free All‐pH Hydrogen Evolution Catalysis by Combined Surface and Dual Electronic Modulation

A combined surface and dual electronic modulation strategy is used to realize metal‐free all‐pH catalysis towards the hydrogen evolution reaction (HER) by coupling a N‐doped carbon framework (MHCF, electron acceptors) derived from MOFs with higher‐Fermi‐level pure carbon nanotubes (CNTs, electron donors), followed by surface modification with carboxyl‐group‐rich polymers. Although the three constituents are inactive, as‐assembled ternary membranes yield superior HER performance with low overpotentials and high durability (≤5 % activity loss over 100 h) at all pH values. The C adjacent to pyrrolic N in MHCF is the most active site and the induced directional interfacial electron transfer from CNTs to MHCF coupled with N‐driven intramolecular electron transfer in MHCF optimizes Gibbs free energy for hydrogen adsorption (ΔG_H*) near zero, while the polymer modulation enables local H⁺ enrichment in acidic media and enhanced water adsorption and activation in neutral and basic media.     

Atomic Arrangement in Metal‐Doped NiS2 Boosts the Hydrogen Evolution Reaction in Alkaline Media

We report a novel modulation strategy by introducing transition metals into NiS₂ nanosheets (NSs) to flexibly optimize the electronic configurations and atomic arrangement. The Co‐NiS₂ NSs exhibit excellent hydrogen evolution reaction (HER) performance with an overpotential of 80 mV at j=10 mA cm^?2 and long‐term stability of 90 h in alkaline media. The turnover frequencies (TOFs) of 0.55 and 4.1 s^?1 at an overpotential of 100 and 200 mV also confirm their remarkable performance. DFT calculations reveal that the surface dopants abnormally sensitize surface Ni‐3d bands in the long‐range order towards higher electron‐transfer activity, acting as the electron‐depletion center. Meanwhile, the high lying surface S‐sites possess substantially high selectivity for splitting the adsorbing H₂O that guarantee the high HER performance within alkaline conditions. This work opens opportunities for enhancing water splitting by atomic‐arrangement‐assisted electronic modulation via a facile doping strategy.     

Oxygen‐Containing Amorphous Cobalt Sulfide Porous Nanocubes as High‐Activity Electrocatalysts for the Oxygen Evolution Reaction in an Alkaline/Neutral Medium

A novel OER electrocatalyst, namely oxygen‐incorporated amorphous cobalt sulfide porous nanocubes (A‐CoS_4.6O_0.6 PNCs), show advantages over the benchmark RuO₂ catalyst in alkaline/neutral medium. Experiments combining with calculation demonstrate that the desirable O* adsorption energy, associated with the distorted CoS_4.6O_0.6 octahedron structure and the oxygen doping, contribute synergistically to the outstanding electrocatalytic activity.     

Molybdenum Phosphosulfide: An Active,Acid‐Stable,Earth‐Abundant Catalyst for the Hydrogen Evolution Reaction

Introducing sulfur into the surface of molybdenum phosphide (MoP) produces a molybdenum phosphosulfide (MoP|S) catalyst with superb activity and stability for the hydrogen evolution reaction (HER) in acidic environments. The MoP|S catalyst reported herein exhibits one of the highest HER activities of any non‐noble‐metal electrocatalyst investigated in strong acid, while remaining perfectly stable in accelerated durability testing. Whereas mixed‐metal alloy catalysts are well‐known, MoP|S represents a more uncommon mixed‐anion catalyst where synergistic effects between sulfur and phosphorus produce a high‐surface‐area electrode that is more active than those based on either the pure sulfide or the pure phosphide. The extraordinarily high activity and stability of this catalyst open up avenues to replace platinum in technologies relevant to renewable energies, such as proton exchange membrane (PEM) electrolyzers and solar photoelectrochemical (PEC) water‐splitting cells.     

Potential‐Cycling Synthesis of Single Platinum Atoms for Efficient Hydrogen Evolution in Neutral Media

Single‐atom catalysts (SACs) have exhibited high activities for the hydrogen evolution reaction (HER) electrocatalysis in acidic or alkaline media, when they are used with binders on cathodes. However, to date, no SACs have been reported for the HER electrocatalysis in neutral media. We demonstrate a potential‐cycling method to synthesize a catalyst comprising single Pt atoms on CoP‐based nanotube arrays supported by a Ni foam, termed PtSA‐NT‐NF. This binder‐free catalyst is centimeter‐scale and scalable. It is directly used as HER cathodes, whose performances at low and high current densities in phosphate buffer solutions (pH 7.2) are comparable to and better than, respectively, those of commercial Pt/C. The Pt mass activity of PtSA‐NT‐NF is 4 times of that of Pt/C, and its electrocatalytic stability is also better than that of Pt/C. This work provides a large‐scale production strategy for binder‐free Pt SAC electrodes for efficient HER in neutral media.     

Surfactant‐Assisted Phase‐Selective Synthesis of New Cobalt MOFs and Their Efficient Electrocatalytic Hydrogen Evolution Reaction

Reported herein are two new polymorphic Co‐MOFs (CTGU‐5 and ‐6) that can be selectively crystallized into the pure 2D or 3D net using an anionic or neutral surfactant, respectively. Each polymorph contains a H₂O molecule, but differs dramatically in its bonding to the framework, which in turn affects the crystal structure and electrocatalytic performance for hydrogen evolution reaction (HER). Both experimental and computational studies find that 2D CTGU‐5 which has coordinates water and more open access to the cobalt site has higher electrocatalytic activity than CTGU‐6 with the lattice water. The integration with co‐catalysts, such as acetylene black (AB) leads to a composite material, AB&CTGU‐5 (1:4) with very efficient HER catalytic properties among reported MOFs. It exhibits superior HER properties including a very positive onset potential of 18 mV, low Tafel slope of 45 mV dec⁻¹, higher exchange current density of 8.6×10⁻⁴ A cm⁻², and long‐term stability.     

Engineering the Coordination Environment of Single‐Atom Platinum Anchored on Graphdiyne for Optimizing Electrocatalytic Hydrogen Evolution

Two Pt single‐atom catalysts (SACs) of Pt‐GDY1 and Pt‐GDY2 were prepared on graphdiyne (GDY)supports. The isolated Pt atoms are dispersed on GDY through the coordination interactions between Pt atoms and alkynyl C atoms in GDY, with the formation of five‐coordinated C₁‐Pt‐Cl₄ species in Pt‐GDY1 and four‐coordinated C₂‐Pt‐Cl₂ species in Pt‐GDY2. Pt‐GDY2 shows exceptionally high catalytic activity for the hydrogen evolution reaction (HER), with a mass activity up to 3.3 and 26.9 times more active than Pt‐GDY1 and the state‐of‐the‐art commercial Pt/C catalysts, respectively. Pt‐GDY2 possesses higher total unoccupied density of states of Pt 5d orbital and close to zero value of Gibbs free energy of the hydrogen adsorption (|Δ |) at the Pt active sites, which are responsible for its excellent catalytic performance. This work can help better understand the structure–catalytic activity relationship in Pt SACs.     

High‐Performance K–CO2 Batteries Based on Metal‐Free Carbon Electrocatalysts

Metal–CO₂ batteries have attracted much attention owing to their high energy density and use of greenhouse CO₂ waste as the energy source. However, the increasing cost of lithium and the low discharge potential of Na–CO₂ batteries create obstacles for practical applications of Li/Na–CO₂ batteries. Recently, earth‐abundant potassium ions have attracted considerable interest as fast ionic charge carriers for electrochemical energy storage. Herein, we report the first K–CO₂ battery with a carbon‐based metal‐free electrocatalyst. The battery shows a higher theoretical discharge potential (E^?=2.48 V) than that of Na–CO₂ batteries (E^?=2.35 V) and can operate for more than 250 cycles (1500 h) with a cutoff capacity of 300 mA h g^?1. Combined DFT calculations and experimental observations revealed a reaction mechanism involving the reversible formation and decomposition of P12₁/c1‐type K₂CO₃ at the efficient carbon‐based catalyst.     

Rational Design of Single Molybdenum Atoms Anchored on N‐Doped Carbon for Effective Hydrogen Evolution Reaction

The highly efficient electrochemical hydrogen evolution reaction (HER) provides a promising pathway to resolve energy and environment problems. An electrocatalyst was designed with single Mo atoms (Mo‐SAs) supported on N‐doped carbon having outstanding HER performance. The structure of the catalyst was probed by aberration‐corrected scanning transmission electron microscopy (AC‐STEM) and X‐ray absorption fine structure (XAFS) spectroscopy, indicating the formation of Mo‐SAs anchored with one nitrogen atom and two carbon atoms (Mo₁N₁C₂). Importantly, the Mo₁N₁C₂ catalyst displayed much more excellent activity compared with Mo₂C and MoN, and better stability than commercial Pt/C. Density functional theory (DFT) calculation revealed that the unique structure of Mo₁N₁C₂ moiety played a crucial effect to improve the HER performance. This work opens up new opportunities for the preparation and application of highly active and stable Mo‐based HER catalysts.     

Large‐Area,Free‐Standing,Two‐Dimensional Supramolecular Polymer Single‐Layer Sheets for Highly Efficient Electrocatalytic Hydrogen Evolution

The rational construction of covalent or noncovalent organic two‐dimensional nanosheets is a fascinating target because of their promising applications in electronics, membrane technology, catalysis, sensing, and energy technologies. Herein, a large‐area (square millimeters) and free‐standing 2D supramolecular polymer (2DSP) single‐layer sheet (0.7–0.9 nm in thickness), comprising triphenylene‐fused nickel bis(dithiolene) complexes has been readily prepared by using the Langmuir–Blodgett method. Such 2DSPs exhibit excellent electrocatalytic activities for hydrogen generation from water with a Tafel slope of 80.5 mV decade⁻¹ and an overpotential of 333 mV at 10 mA cm⁻², which are superior to that of recently reported carbon nanotube supported molecular catalysts and heteroatom‐doped graphene catalysts. This work is promising for the development of novel free‐standing organic 2D materials for energy technologies.     

Superhydrophilic Phytic‐Acid‐Doped Conductive Hydrogels as Metal‐Free and Binder‐Free Electrocatalysts for Efficient Water Oxidation

Recently, metal‐free, heteroatom‐doped carbon nanomaterials have emerged as promising electrocatalysts for the oxygen evolution reaction (OER), but their synthesis is a tedious process involving energy‐wasting calcination. Molecular electrocatalysts offer attractive catalysts for the OER. Here, phytic acid (PA) was selected to investigate the OER activity of carbons in organic molecules by DFT calculations and experiments. Positively charged carbons on PA were very active towards the OER. The PA molecules were fixed into a porous, conductive hydrogel with a superhydrophilic surface. This outperformed most metal‐free electrocatalysts. Besides the active sites on PA, the high OER activity was also related to the porous and conductive networks on the hydrogel, which allowed fast charge and mass transport during the OER. Therefore, this work provides a metal‐free, organic‐molecule‐based electrocatalyst to replace carbon nanomaterials for efficient OER.     

Sulfur and Nitrogen Codoped Carbon Tubes as Bifunctional Metal‐Free Electrocatalysts for Oxygen Reduction and Hydrogen Evolution in Acidic Media

Invited for the cover of this issue is the group of Qiang Wu and Zheng Hu at Nanjing University. The image depicts sulfur and nitrogen codoped carbon tubes as bifunctional metal‐free electrocatalysts for oxygen reduction and hydrogen evolution in acidic media. Read the full text of the article at 10.1002/chem.201601535 .     

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.     

Ni3FeN‐Supported Fe3Pt Intermetallic Nanoalloy as a High‐Performance Bifunctional Catalyst for Metal–Air Batteries

Electrocatalysts for both the oxygen reduction and evolution reactions (ORR and OER) are vital for the performances of rechargeable metal–air batteries. Herein, we report an advanced bifunctional oxygen electrocatalyst consisting of porous metallic nickel‐iron nitride (Ni₃FeN) supporting ordered Fe₃Pt intermetallic nanoalloy. In this hybrid catalyst, the bimetallic nitride Ni₃FeN mainly contributes to the high activity for the OER while the ordered Fe₃Pt nanoalloy contributes to the excellent activity for the ORR. Robust Ni₃FeN‐supported Fe₃Pt catalysts show superior catalytic performance to the state‐of‐the‐art ORR catalyst (Pt/C) and OER catalyst (Ir/C). The Fe₃Pt/Ni₃FeN bifunctional catalyst enables Zn–air batteries to achieve a long‐term cycling performance of over 480 h at 10 mA cm⁻² with high efficiency. The extraordinarily high performance of the Fe₃Pt/Ni₃FeN bifunctional catalyst makes it a very promising air cathode in alkaline electrolyte.