Efficient water splitting through electrocatalysis holds great promise for producing hydrogen fuel in modern energy devices. Its real application however suffers from sluggish reaction kinetics due to the lack of high-performance catalysts except noble metals such as platinum. Herein, we report an active system of plasmonic-metal Au nanorods/molybdenum disulfide (MoS2) nanosheets hybrids for the hydrogen evolution reaction (HER). The plasmonic Au-MoS2 hybrids dramatically improve the HER, leading to a ∼3-fold increase of current under excitation of Au localized surface plasmon resonance (LSPR). A turnover of 8.76 s(-1) at 300 mV overpotential is measured under LSPR excitation, which by far exceeds the activity of MoS2 catalysts reported recently. The HER enhancement can be largely attributed to the increase of carrier density in MoS2 induced by the injection of hot electrons of Au nanorods. We demonstrate that the synergistic effect of the hole scavengers can further facilitate electron-hole separation, resulting in a decrease of the overpotential of HER at MoS2 to ∼120 mV. This study highlights how metal LSPR activates the HER and promises novel opportunities for enhancing intrinsic activities of semiconducting materials.

In many green electrochemical energy devices, the conversion between oxygen and water suffers from high potential loss due to the difficulty in decreasing activation energy. Overcoming this issue requires full understanding of global reactions and development of strategies in efficient catalyst design. Here we report an active copper nanocomposite, inspired by natural coordination environments of catalytic sites in an enzyme, which catalyzes oxygen reduction/evolution at potentials closely approaching standard potential. Such performances are related to the imperfect coordination configuration of the copper(II) active site whose electron density is tuned by neighbouring copper(0) and nitrogen ligands incorporated in graphene. The electron transfer number of oxygen reduction is estimated by monitoring the redox of hydrogen peroxide, which is determined by the overpotential and electrolyte pH. An in situ fluorescence spectroelectrochemistry reveals that hydroxyl radical is the common intermediate for the electrochemical conversion between oxygen and water.

The crystal phase of metal nanocatalysts significantly affects their catalytic performance. Cu-based nanomaterials are unique electrocatalysts for CO2 reduction reaction (CO2RR) to produce high-value hydrocarbons. However, studies to date are limited to the conventional face-centered cubic (fcc) Cu. Here, we report a crystal phase-dependent catalytic behavior of Cu, after the successful synthesis of high-purity 4H Cu and heterophase 4H/fcc Cu using the 4H and 4H/fcc Au as templates, respectively. Remarkably, the obtained unconventional crystal structures of Cu exhibit enhanced overall activity and higher ethylene (C2H4) selectivity in CO2RR compared to the fcc Cu. Density functional theory calculations suggest that the 4H phase and 4H/fcc interface of Cu favor the C2H4 formation pathway compared to the fcc Cu, leading to the crystal phase-dependent C2H4 selectivity. This study demonstrates the importance of crystal phase engineering of metal nanocatalysts for electrocatalytic reactions, offering a new strategy to prepare novel catalysts with unconventional phases for various applications.

Molecularly sized and heterogeneous Ni-Fe sites on graphene serve as efficient electrocatalysts.

Molecular Co ions were grafted onto doped graphene in a coordination environment, resulting in the formation of molecularly well-defined, highly active electrocatalytic sites at a heterogeneous interface for the oxygen evolution reaction (OER). The S dopants of graphene are suggested to be one of the binding sites and to be responsible for improving the intrinsic activity of the Co sites. The turnover frequency of such Co sites is greater than that of many Co-based nanostructures and IrO catalysts. Through a series of carefully designed experiments, the pathway for the evolution of the Co cation-based molecular catalyst for the OER was further demonstrated on such a single Co-ion site for the first time. The Co ions were successively oxidized to Co and Co states prior to the OER. The sequential oxidation was coupled with the transfer of different numbers of protons/hydroxides and generated an active Co═O fragment. A side-on hydroperoxo ligand of the Co site is proposed as a key intermediate for the formation of dioxygen.

Immobilization of planar CoII‐2,3‐naphthalocyanine (NapCo) complexes onto doped graphene resulted in a heterogeneous molecular Co electrocatalyst that was active and selective to reduce CO2 into CO in aqueous solution. A systematic study revealed that graphitic sulfoxide and carboxyl dopants of graphene were the efficient binding sites for the immobilization of NapCo through axial coordination and resulted in active Co sites for CO2 reduction. Compared to carboxyl dopants, the sulfoxide dopants further improved the electron communication between NapCo and graphene, which led to the increase of turnover frequency of the Co sites by about 3 times for CO production with a Faradic efficiency up to 97 %. Pristine NapCo in the absence of a graphene support did not display efficient electron communication with the electrode and thus failed to serve as the electrochemical active site for CO2 reduction under the identical conditions.

We report that a structurally simple molecular 1,10-phenanthroline-Cu complex on a mesostructured graphene matrix can be active and selective toward CO2 reduction over H2 evolution in an aqueous solution. The active sites consisted of Cu(I) center in a 2 distorted trigonal bipyramidal geometry, which enabled the adsorption of CO2 with η 1 -COO-like configuration to commence the catalysis, with a turnover frequency of ~45 s -1 at -1 V vs reversible hydrogen electrode. Using in-situ infrared spectroelectrochemical investigation, we demonstrated that the Cu complex was reversibly heterogenized near graphene surface via potential control. An increase of electron density in the complex was observed as a result of the interaction from the electric field, which further tuned the electron distribution in the neighboring CO2. It was also found that the mesostructure of graphene matrix favored CO2 reduction on the Cu center over hydrogen evolution by limiting mass transport from the bulk solution to the electrode surface.Received: ((will be filled in by the editorial staff)) Revised: ((will be filled in by the editorial staff))

renewable energy resources should be integrated with some energy storage and conversion devices. [10,11] In particular, the electrochemical splitting of water to generate hydrogen (H 2 ) and oxygen (O 2 ) seems to provide an appealing solution through conversion of the electrical input driven by the intermittent energies into stable chemical fuel. [12][13][14][15] As H 2 contains the highest specific energy (141.86 MJ kg −1 ) than all chemicals, it is considered to be a promising energy carrier. The strategy of electrochemical water splitting is conceptually simple, as illustrated by Figure 1. In a typical water-electrolysis cell, the cathode and anode are incorporated into compartmentalized spaces separated by an ion-exchange membrane. As the electron flow passes through the circuit, protons (or water molecules) are reduced into H 2 at the cathode, termed as the hydrogen-evolution reaction (HER); in the meantime, water molecules (or hydroxide ions) are oxidized into O 2 at the anode, termed as the oxygen-evolution reaction (OER). The thermodynamic voltage to commence water splitting is commonly greater than 1.23 V, whereas to achieve high reaction rates, an additional driving force in the form of an overpotential (η) (around 0.7 to 1.0 V) [16] is needed to overcome the kinetic barriers of both the HER and the OER, which determines the conversion efficiency, from electrical to chemical energy.To minimize the η while maintaining the high efficiencies of energy conversion, the electrodes in a water electrolyzer are modified with active and stable electrocatalysts to increase the rates of the electrochemical reactions. The cathodic HER involves two-electron transfer and one central intermediate, known as the atomic H chemisorbed on the electrocatalyst surfaces (H*). Its elemental steps are depicted through either the Volmer-Heyrovsky or the Volmer-Tafel mechanism, as seen in Reaction equation (1) to (5): i) Volmer step: