The recent advances in 1D and 2D metallic nanostructures for electrochemical water splitting (HER and OER) are highlighted.

Metal-organic frameworks (MOFs) are a class of promising materials for diverse heterogeneous catalysis, but they are usually not directly employed for oxygen evolution electrocatalysis. Most reports focus on using MOFs as templates to in situ create efficient electrocatalysts through annealing. Herein, we prepared a series of Fe/Ni-based trimetallic MOFs (Fe/Ni/Co(Mn)-MIL-53 accordingly to the Material of Institute Lavoisier) by solvothermal synthesis, which can be directly adopted as highly efficient electrocatalysts. The Fe/Ni/Co(Mn)-MIL-53 shows a volcano-type oxygen evolution reaction (OER) activity as a function of compositions. The optimized Fe/Ni /Co -MIL-53 can reach a current density of 20 mA cm at low overpotential of 236 mV with a small Tafel slope of 52.2 mV dec . In addition, the OER performance of these MOFs can be further enhanced by directly being grown on nickel foam (NF).

Pursuing active and durable water splitting electrocatalysts is of vital significance for solving the sluggish kinetics of the oxygen evolution reaction (OER) process in energy supply. Herein, theoretical calculations identify that the local distortion-strain effect in amorphous RuTe2 system abnormally sensitizes the Te-pπ coupling capability and enhances the electron-transfer of Ru-sites, in which the excellent inter-orbital p-d transfers determine strong electronic activities for boosting OER performance. Thus, a robust electrocatalyst based on amorphous RuTe2 porous nanorods (PNRs) is successfully fabricated. In the acidic water splitting, a-RuTe2 PNRs exhibit a superior performance, which only require a cell voltage of 1.52 V to reach a current density of 10 mA cm−2. Detailed investigations show that the high density of defects combine with oxygen atoms to form RuOxHy species, which are conducive to the OER. This work offers valuable insights for constructing robust electrocatalysts based on theoretical calculations guided by rational design and amorphous materials.

Carbon dioxide (CO2) hydrogenation to ethanol (C2H5OH) is considered a promising way for CO2 conversion and utilization, whereas desirable conversion efficiency remains a challenge. Herein, highly active, selective and stable CO2 hydrogenation to C2H5OH was enabled by highly ordered Pd-Cu nanoparticles (NPs). By tuning the composition of the Pd-Cu NPs and catalyst supports, the efficiency of CO2 hydrogenation to C2H5OH was well optimized with Pd2Cu NPs/P25 exhibiting high selectivity to C2H5OH of up to 92.0% and the highest turnover frequency of 359.0 h–1. Diffuse reflectance infrared Fourier transform spectroscopy results revealed the high C2H5OH production and selectivity of Pd2Cu NPs/P25 can be ascribed to boosting *CO (adsorption CO) hydrogenation to *HCO, the rate-determining step for the CO2 hydrogenation to C2H5OH.

The renewable electricity-driven reduction of carbon dioxide (CO 2 RR) is a promising technology for carbon utilization. However, it is still a challenge to broaden the application of CO 2 RR. Herein, we report a Te-doped Pd nanocrystals (Te−Pd NCs) for promoting urea synthesis by coupling CO 2 RR with electrochemical reduction of nitrite. The electrochemical synthesis of urea has been achieved with nearly 12.2% Faraday efficiency (FE) and 88.7% N atom efficiency (NE) at −1.1 V versus reversible hydrogen electrode (vs RHE), much higher than those of pure Pd NCs (4.2% FE and 21.8% NE). Significantly, an FE of ∼10.2% and an NE of ∼82.3% for urea solution production via an optimized flow cell system have been realized, where a solution with up to 0.95 wt % of urea has been obtained. Mechanistic insights show that Te-doping not only optimizes the CO 2 / CO adsorption but also promotes NH 3 production, fully meeting the requirements of urea synthesis.

more promising approach to generating H 2 with high purity. Electrochemical water splitting, driven by renewable electricity, proceeds through hydrogen evolution reaction (HER) at the cathode side and oxygen evolution reaction (OER) at the anode side of an electrochemical cell. [7,10] The HER, a two-electron transfer process, is the simplest electrochemical reaction and relatively easy to occur. On the contrary, OER involving four-electron transfer is a much more complicated multistep reaction. A considerably large overpotential is thus added to the actual water splitting process because of the complexity of OER, leading to sluggish reaction kinetics and distinctly reducing the energy efficiency. [11] Therefore, efficient electrocatalysts with high activity and durable stability are needed to overcome the high energy barrier.OER is an electrochemical process of producing molecular O 2 through a series of proton-electron coupled steps. [12][13][14] Depending on the pH of the electrolytes, the reaction pathways of producing O 2 are totally different. In alkaline electrolytes, hydroxyl groups (OH − ) are oxidized and converted to H 2 O and O 2 . In acidic media, two water molecules (H 2 O) are oxidized generating four protons (H + ) and O 2 . Compared to acidic OER, alkaline OER possesses more favorable reaction kinetics because of the abundant hydroxyl groups in the electrolyte. For acidic OER, however, the break of the strong covalent OH bond of H 2 O requires high energy thus leading to more sluggish kinetics. Another advantage for alkaline OER lies in the wide range of catalysts such as transition metal (e.g., Ni, Co, and Fe) based oxides and hydroxides as well as carbon materials. [15][16][17][18][19][20][21][22] The electrocatalysts for acidic OER are mostly related to iridium (Ir) and ruthenium (Ru) based materials currently. [19,[23][24][25][26][27][28][29][30][31] In spite of the more favorable kinetics and wide range of catalysts for alkaline OER, however, acidic OER is more preferable than alkaline OER because of the diversified advantages of proton exchange membrane water electrolyzers over alkaline water electrolyzers. [19,23] Proton exchange membrane (PEM) is an acidic solid polymer electrolyte membrane with much smaller gas crossover than that of the alkaline solid polymer, which can ensure a larger load range and much safer operation of an acidic electrolyzer by largely avoiding forming H 2 /O 2 mixture. [32] Furthermore, the fully developed PEMs can provide high proton conductivity, resulting in low Ohmic loss and high current density. [32] Proton exchange membrane (PEM) water electrolyzers hold great significance for renewable energy storage and conversion. The acidic oxygen evolution reaction (OER) is one of the main roadblocks that hinder the practical application of PEM water electrolyzers. Highly active, cost-effective, and durable electrocatalysts are indispensable for lowering the high kinetic barrier of OER to achieve boosted reaction kinetics. To date, a wide spectrum of advanced electroca...

The development of bifunctional electrocatalysts for overall water splitting in acidic media is vital for polymer electrolyte membrane (PEM) electrolyzers, but still full of obstacles. Here, highly efficient acidic overall water splitting is realized by utilizing ultrasmall, monodispersed Iridium (Ir)‐based nanoclusters (NCs) as the candidate, via a surfactant‐free, wet‐chemical, and large‐scalable strategy. Benefiting from the high specific surface area, clean surface, and strong binding between NCs and supports, the IrM NCs exhibit attractive activities and durability for both oxygen evolution reaction and hydrogen evolution reaction in acidic electrolytes, with IrNi NCs showing the best performance. More significantly, in the overall water splitting, IrNi NCs reach 10 mA cm−2 at a cell voltage of only 1.58 V in 0.5 m H2SO4 electrolyte, holding promises for potential implementation of PEM water electrolysis. This work opens a new avenue toward designing bifunctional “acidic stable” catalysts for efficient overall water splitting.

One of the most critical aspects in the preparation of single-walled carbon nanotubes (SWCNTs)/ conducting polymer hybrid electrodes is to improve the energy density without seriously deteriorating their high power capability. Here, we report a ''skeleton/skin'' strategy for the preparation of freestanding, thin and flexible SWCNT/polyaniline (PANI) hybrid films by a simple in situ electrochemical polymerization method using directly grown SWCNT films with a continuous reticulate structure as template. In situ electrochemical polymerization can achieve effective deposition of PANI onto the surface of SWCNT bundles in the films and control the morphology and microstructure of the SWCNT/PANI hybrid films. In a SWCNT/PANI hybrid film, the directly grown SWCNT film with continuous reticulate architecture acts as the skeleton and PANI layers act as the skin. This unique continuous ''skeleton/skin'' structure ensures that these hybrid films have much higher conductivity compared to SWCNT/PANI composite films based on post-deposition SWCNT films. Flexible supercapacitors have been fabricated using the SWCNT/PANI hybrid films as both electrodes and charge collectors without metallic current collectors. High energy and power densities (131 W h kg À1 and 62.5 kW kg À1 , respectively) have been achieved for the optimized assembly. The high electrical conductivity and flexibility, in combination with continuous porous architecture, suggests that the asprepared ultrathin free-standing SWCNT/PANI hybrid films have significant potential as promising electrode materials for thin, lightweight and flexible energy storage devices with high performance. Broader contextThe hybrid electrodes of SWCNT/conducting polymer display high energy density due to pseudocapacitance originating from the conducting polymer. However, their power density is dramatically reduced in comparison with pure SWCNT-based electrodes, due to the poor electrical conductivity of PANI layers and overlapped PANI-PANI contact. Therefore, one of the most critical aspects in the development of SWCNT/conducting polymer supercapacitors is to optimize the energy density without deteriorating their high power capability as these two parameters determine concomitantly the ultimate performance of the supercapacitor. In this work, we report a ''skeleton/skin'' strategy to prepare free-standing, thin and flexible SWCNT/PANI hybrid films by a simple in situ electrochemical polymerization method using directly grown SWCNT films with continuous reticulate structure as template. The high electrical conductivity and flexibility, in combination with continuous porous architecture, suggest that as-prepared ultrathin freestanding SWCNT/PANI hybrid films have significant potential as promising electrode materials for thin, lightweight and flexible energy storage devices with high performance. The flexible supercapacitors based on the SWCNT/PANI hybrid films achieve high energy and power densities. 8726