No abstract

Electrochemical water splitting plays a crucial role in the development of clean and renewable energy production and conversion, which is a promising pathway to reduce social dependence on fossil fuels. Thus, highly active, cost‐efficient, and robust catalysts must be developed to reduce the reaction overpotential and increase electrocatalytic efficiency. In this review, recent research efforts toward developing advanced electrocatalysts based on noble metals with outstanding performance for water splitting catalysis, which is mainly dependent on their structure engineering, are summarized. First, a simple description of the water‐splitting mechanism and some promising structure engineering strategies are given, including heteroatom incorporation, strain engineering, interface/hybrid engineering, and single atomic construction. Then, the underlying relationship between noble metal electronic/geometric structure and performance for water splitting is discussed with the assistance of theoretical simulation. Finally, a personal perspective is provided in order to highlight the challenges and opportunities for developing novel electrocatalysts suitable for a wide range of commercial uses in water splitting for structural engineering applications.

Selectively exposing active surfaces and judiciously tuning the near-surface composition of electrode materials represent two prominent means of promoting electrocatalytic performance. Here, a new class of Pt Fe zigzag-like nanowires (Pt-skin Pt Fe z-NWs) with stable high-index facets (HIFs) and nanosegregated Pt-skin structure is reported, which are capable of substantially boosting electrocatalysis in fuel cells. These unique structural features endow the Pt-skin Pt Fe z-NWs with a mass activity of 2.11 A mg and a specifc activity of 4.34 mA cm for the oxygen reduction reaction (ORR) at 0.9 V versus reversible hydrogen electrode, which are the highest in all reported PtFe-based ORR catalysts. Density function theory calculations reveal a combination of exposed HIFs and formation of Pt-skin structure, leading to an optimal oxygen adsorption energy due to the ligand and strain effects, which is responsible for the much enhanced ORR activities. In contrast to previously reported HIFs-based catalysts, the Pt-skin Pt Fe z-NWs maintain ultrahigh durability with little activity decay and negligible structure transformation after 50 000 potential cycles. Overcoming a key technical barrier in electrocatalysis, this work successfully extends the nanosegregated Pt-skin structure to nanocatalysts with HIFs, heralding the exciting prospects of high-effcient Pt-based catalysts in fuel cells.

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.

Core/shell nanocatalysts are ac lass of promising materials,w hicha chieve the enhanced catalytic activities through the synergy between ligand effect and strain effect. However,i th as been challenging to disentangle the contributions from the two effects,whichhinders the rational design of superior core/shell nanocatalysts.H erein, we report precise synthesis of PdCu/Ir core/shell nanocrystals,w hichc an significantly boost oxygen evolution reaction (OER) via the exclusive strain effect. The heteroepitaxial coating of four Ir atomic layers onto PdCu nanoparticle gives arelatively thickIr shell eliminating the ligand effect, but creates ac ompressive strain of ca. 3.60%. The strained PdCu/Ir catalysts can deliver al ow OER overpotential and ah igh mass activity.D ensity functional theory (DFT) calculations reveal that the compressive strain in Ir shell downshifts the d-band center and weakens the binding of the intermediates,c ausing the enhanced OER activity.The compressive strain also boosts hydrogen evolution reaction (HER) activity and the strained nanocrystals can be served as excellent catalysts for both anode and cathode in overall water-splitting electrocatalysis.

resource along with high gravimetric energy density. [2] In this respect, the electrochemical or photoelectrochemical splitting of water into hydrogen and oxygen has been regarded as a potential and clean technology to meet large-scale energy demands in the future. [3] However, water splitting is an unfavorable process due to its thermodynamic barrier, especially for the one-half reaction: oxygen evolution reaction (OER) involving four sequential proton-coupled electron transfer steps. [4] For the effective water-splitting catalysis, an advanced material should not only increase the reaction rate, but also lower the overpotential for full water splitting. Up to now, the commercial hydrogen evolution reaction (HER) catalysts consist of Pt group materials and RuO x /IrO x are considered as the best catalysts for catalyzing OER. [5] Unfortunately, the scarcity and high cost of noble metals limit their widespread use. Hence, to develop effective and earth-abundant alternative catalysts remain a critical task for extensive application of water splitting. Recently, great efforts have been devoted to designing novel structure and exploring advanced electrocatalysts based on earth-abundant elements with high activity, low-cost, and high tolerance. Some promising transition-metal compounds for catalyzing HER include M x P (M = Ni, Co, Fe,The development of cost-efficient, active, and stable electrode materials as bifunctional catalysts for electrochemical water splitting is crucial to highperformance renewable energy storage and conversion devices. In this work, the synthesis of Co-based multi-metal borides nanochains with amorphous structure is reported for boosting the oxygen evolution (OER) and hydrogen evolution reactions (HER) by one-pot NaBH 4 reduction of Co 2+ , Ni 2+ , and Fe 2+ under ambient temperature. In all the investigated Co-based metal borides, NiCoFeB nanochains show the excellent OER performance with a low overpotential of 284 mV at 10 mA cm -2 and Tafel slope of 46 mV dec -1 , respectively, together with excellent catalytic stability, and robust HER performance with an overpotential of 345 mV at 10 mA cm -2 . The density functional theory (DFT) calculations reveal that the excellent electrocatalytic performance is mainly attributed to optimal electronic structure by tuning the Co-3d band activities by the incorporation of Ni and Fe for enhanced water splitting via the potentially existed Co 0 state. Moreover, the electrolyzer using NiCoFeB nanochains as anode and cathode offers 10 mA cm -2 at a cell voltage of 1.81 V, comparable to commercial Pt/C // Ir/C, providing a simple method to design and explore highly efficient and cheap bifunctional electrocatalysts for overall water splitting.

Exploring a simple, fast, solvent-free synthetic method for large-scale preparation of cheap, highly active electrocatalysts for industrial hydrogen evolution reaction is one of the most promising work today. In this work, a simple, fast and solvent-free microwave pyrolysis method is used to synthesize ultra-small (3.5 nm) Ru-Mo2C@CNT catalyst with heterogeneous structure and strong metal-support interaction in one step. The Ru-Mo2C@CNT catalyst only exhibits an overpotential of 15 mV at a current density of 10 mA cm−2, and exhibits a large turnover frequency value up to 21.9 s−1 under an overpotential of 100 mV in 1.0 M KOH. In addition, this catalyst can reach high current densities of 500 mA cm−2 and 1000 mA cm−2 at low overpotentials of 56 mV and 78 mV respectively, and it displays high stability of 1000 h. This work provides a feasible way for the reasonable design of other large-scale production catalysts.

Two dimensional (2D), ordered intermetallic and core/shell architectures are highly desirable structural features for promoting electrocatalysis on Pt-based nanocrystals in terms of activity, durability, and cost. However, it is currently an extreme challenge to achieve all these features in a single catalytic nanostructure. Herein, we report a new class of 2D nanoplate catalyst composed of intermetallic hcp-PtBi core and ultrathin fcc-Pt shell synthesized by a facile one-pot wet-chemical approach. The unique structural features of PtBi/Pt core/shell nanoplates make them exhibit the highest oxygen reduction reaction (ORR) activity in all the reported PtBi-based catalytic systems and 5 times more active than commercial Pt/C catalyst for ORR. The combination of cyclic voltammograms, X-ray photoelectron spectroscopy, and density functional theory calculations reveals that an optimal oxygen adsorption energy and efficient reduction on both edge surface and interface regions between Pt-shell and PtBi-core from hcp-PtBi/fcc-Pt core/shell nanoplates relative to that on commercial Pt, deriving from the Bi-p empty band suppression at the core/shell interface, is the key to greatly boosting the ORR activity of the PtBi nanocatalyst system. The PtBi-Pt interface performs at relatively lower overpotential compared with the edge surface because of excellent reduction from OH to the H2O. Thanks to the intermetallic phase and core/shell architecture, hcp-PtBi/fcc-Pt core/shell nanoplates show little loss in electrochemically active surface area and ORR activity during the accelerated durability test. They also show enhanced catalytic performance for the electro-oxidation of liquid fuels in both acid and alkaline electrolytes. This work sheds light on the rational design of new 2D core/shell nanostructured catalysts for enhancing fuel-cell electrocatalysis.