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 Fe 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 , and only 8 mV of polarization-curve shift after a 1000-cycle durability test in 0.5 m H SO 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.

The grand challenge in the development of atomically dispersed metallic catalysts is their low metal-atom loading density, uncontrollable localization and ambiguous interactions with supports, posing difficulty in maximizing their catalytic performance. Here, we achieve an interface catalyst consisting of atomic cobalt array covalently bound to distorted 1T MoS2 nanosheets (SA Co-D 1T MoS2). The phase of MoS2 transforming from 2H to D-1T, induced by strain from lattice mismatch and formation of Co-S covalent bond between Co and MoS2 during the assembly, is found to be essential to form the highly active single-atom array catalyst. SA Co-D 1T MoS2 achieves Pt-like activity toward HER and high long-term stability. Active-site blocking experiment together with density functional theory (DFT) calculations reveal that the superior catalytic behaviour is associated with an ensemble effect via the synergy of Co adatom and S of the D-1T MoS2 support by tuning hydrogen binding mode at the interface.

The development of highly efficient and durable electrocatalysts for high-performance overall water-splitting devices is crucial for clean energy conversion. However, the existing electrocatalysts still suffer from low catalytic efficiency, and need a large overpotential to drive the overall water-splitting reactions. Herein, we report an iridium–tungsten alloy with nanodendritic structure (IrW ND) as a new class of high-performance and pH-universal bifunctional electrocatalysts for hydrogen and oxygen evolution catalysis. The IrW ND catalyst presents a hydrogen generation rate ∼2 times higher than that of the commercial Pt/C catalyst in both acid and alkaline media, which is among the most active hydrogen evolution reaction (HER) catalysts yet reported. The density functional theory (DFT) calculations reveal that the high HER intrinsic catalytic activity results from the suitable hydrogen and hydroxyl binding energies, which can accelerate the rate-determining step of the HER in acid and alkaline media. Moreover, the IrW NDs show superb oxygen evolution reaction (OER) activity and much improved stability over Ir. The theoretical calculation demonstrates that alloying Ir metal with W can stabilize the formed active iridium oxide during the OER process and lower the binding energy of reaction intermediates, thus improving the Ir corrosion resistance and OER kinetics. Furthermore, the overall water-splitting devices driven by IrW NDs can work in a wide pH range and achieve a current density of 10 mA cm–2 in acid electrolyte at a low potential of 1.48 V.

The development of new electrocatalysts with high activity and durability for alcohol oxidation is an emerging need of direct alcohol fuel cells. However, the commonly used Pt‐based catalysts still exhibit drawbacks including limited catalytic activity, high overpotential, and severe CO poisoning. Here a general approach is reported for preparing ultrathin PtNiM (M = Rh, Os, and Ir) nanowires (NWs) with excellent anti‐CO‐poisoning ability and high activity. Owing to their superior nanostructure and optimal electronic interaction, the ultrathin PtNiM NWs show enhanced electrocatalytic performance for both methanol oxidation reaction (MOR) and ethanol oxidation reaction (EOR). The optimal PtNiRh NWs show mass activity of 1.72 A mg−1 and specific activity of 2.49 mA cm−2 for MOR, which are 3.17 and 2.79 times higher than those of Pt/C. In particular, the onset potentials of PtNiRh NWs for MOR and EOR shift down by about 65 and 85 mV compared with those of Pt/C. Density functional theory calculations further verify their high antipoison properties for MOR and EOR from both an electronic and energetic perspective. Facilitated by the introduction of Rh and Ni, the stable pinning of the Pt 5d band associated with electron‐rich and depletion centers solves the dilemma between reactivity and anti‐CO poisoning.

Proton exchange membrane (PEM)-based water-splitting electrolyzers have been considered as the most promising hydrogen production technology with great advantages including low Ohmic loss, high electrolyzer efficiency, and large partial load range. [1] However, most developed non-noble metal-based hydrogen/oxygen evolution electrocatalysts are usually not stable in the severe corrosive acidic environment in PEM electrolyzers, [2] which makes the utilization of noble metal indispensable. Moreover, the overall energy conversion efficiency of water-splitting devices is greatly depended on the activity of catalysts both at cathode and anode. [1,3] Therefore, developing electrocatalysts with high activity and corrosion resistant at minimized noble metal content is of great significance toward large-scale hydrogen generation through PEM electrolyzers.Among all the noble metals, Ir-based materials have been regarded as the efficient oxygen evolution reaction (OER) catalysts for their superior activity as well as stability in acidic media. [4] In addition, recent works also indicate the potential of Ir as good catalysts toward hydrogen evolution reaction (HER), even comparable to Pt. [5] Unfortunately, the further application of Ir still suffers from its high cost and scarcity, which greatly limits the widespread adoption of PEM electrolysis. Modulating the nanostructure of catalysts with high surface area stands for one of effective methods to improve the atomic utilization. [6] A series of different Ir-based nanostructures, such as nanoparticles, [7] porous/laminar nanosheets, [8] nanowires, [9] nanotubes, [10] etc., have been reported with enhanced catalytic activity. Among these various shape-controlled nanostructures, 3D flower-like architectures are equipped with abundant catalytic sites, meanwhile have antiaggregation properties in the drastic reaction. [11] Furthermore, alloying Ir with other 3d transition metals is the other valid strategy to decrease the content as well as increase the intrinsic activity of Ir. [12] In these cases, the optimized adsorption energy on the catalysts has been obtained with modified electronic distribution through alloying. However, as for HER on Ir-based alloy, though similar promotion on the catalytic activity compared with Ir metal has been reported, [13] the HER descriptor could be attributed to the hydrogen binding energy (HBE) in acidic solution. [14] The internal relationship Hydrogen production through proton exchange membrane water electrolyzers (PEMWE) requires more active and stable electrocatalysts in acidic media. Herein, a class of Ir-based alloys is reported with flower-like structure as excellent electrocatalysts both for hydrogen and oxygen generation in acid. Specially, the IrNi alloy nanoflowers (IrNi NFs) present the best hydrogen evolution reaction (HER) performance, revealed by a low Tafel slope and overpotential at current density of 10 mA cm −2 , exceeding the commercial Pt/C. It is discovered that alloying Ir with Ni can decrease the hydrogen binding e...