Enhancing the alkaline hydrogen evolution reaction activity through the bifunctionality of Ni(OH)2/metal catalysts

Promoting Effect of Ni(OH)2 on Palladium Nanocrystals Leads to Greatly Improved Operation Durability for Electrocatalytic Ethanol Oxidation in Alkaline Solution

Most electrocatalysts for the ethanol oxidation reaction suffer from extremely limited operational durability and poor selectivity toward the CC bond cleavage. In spite of tremendous efforts over the past several decades, little progress has been made in this regard. This study reports the remarkable promoting effect of Ni(OH)₂ on Pd nanocrystals for electrocatalytic ethanol oxidation reaction in alkaline solution. A hybrid electrocatalyst consisting of intimately mixed nanosized Pd particles, defective Ni(OH)₂ nanoflakes, and a graphene support is prepared via a two-step solution method. The optimal product exhibits a high mass-specific peak current of >1500 mA mg^-1_Pd , and excellent operational durability forms both cycling and chronoamperometric measurements in alkaline solution. Most impressively, this hybrid catalyst retains a mass-specific current of 440 mA mg^-1 even after 20 000 s of chronoamperometric testing, and its original activity can be regenerated via simple cyclic voltammetry cycles in clean KOH. This great catalyst durability is understood based on both CO stripping and in situ attenuated total reflection infrared experiments suggesting that the presence of Ni(OH)₂ alleviates the poisoning of Pd nanocrystals by carbonaceous intermediates. The incorporation of Ni(OH)₂ also markedly shifts the reaction selectivity from the originally predominant C2 pathway toward the more desirable C1 pathway, even at room temperature.

Electrocatalytic hydrogen evolution reaction activity comparable to platinum exhibited by the Ni/Ni(OH)2/graphite electrode

Electrochemical dual-pulse plating with sequential galvanostatic and potentiostatic pulses has been used to fabricate an electrocatalytically active Ni/Ni(OH)₂/graphite electrode. This electrode design strategy to generate the Ni/Ni(OH)₂ interface on graphite from Ni deposits is promising for electrochemical applications and has been used by us for hydrogen generation. The synergetic effect of nickel, colloidal nickel hydroxide islands, and the enhanced surface area of the graphite substrate facilitating HO-H cleavage followed by H(ad) recombination, results in the high current density [200 mA/cm² at an overpotential of 0.3 V comparable to platinum (0.44 V)]. The easy method of fabrication of the electrode, which is also inexpensive, prompts us to explore its use in fabrication of solar-driven electrolysis.

Cactus-Like Hollow Cu2-x S@Ru Nanoplates as Excellent and Robust Electrocatalysts for the Alkaline Hydrogen Evolution Reaction

The development of Pt-free electrocatalysts for the hydrogen evolution reaction (HER) recently is a focus of great interest. While several strategies are developed to control the structural properties of non-Pt catalysts and boost their electrocatalytic activities for the HER, the generation of highly reactive defects or interfaces by combining a metal with other metals, or with metal oxides/sulfides, can lead to notably enhanced catalytic performance. Herein, the preparation of cactus-like hollow Cu_2-x S@Ru nanoplates (NPs) that contain metal/metal sulfide heterojunctions and show excellent catalytic activity and durability for the HER in alkaline media is reported. The initial formation of Ru islands on presynthesized Cu_1.94 S NPs, via cation exchange between three Cu⁺ ions and one Ru³⁺ , induces the growth of the Ru phase, which is concomitant with the dissolution of the Cu_1.94 S nanotemplate, culminating in the formation of a hollow nanostructure with numerous thin Ru pillars. Hollow Cu_2-x S@Ru NPs exhibit a small overpotential of 82 mV at a current density of -10 mA cm^-2 and a low Tafel slope of 48 mV dec^-1 under alkaline conditions; this catalyst is among state-of-the-art HER electrocatalysts in alkaline media. The excellent performance of hollow Cu_2-x S@Ru NPs originates from the facile dissociation of water in the Volmer step.

Efficient hydrogen production on MoNi4 electrocatalysts with fast water dissociation kinetics

Various platinum-free electrocatalysts have been explored for hydrogen evolution reaction in acidic solutions. However, in economical water-alkali electrolysers, sluggish water dissociation kinetics (Volmer step) on platinum-free electrocatalysts results in poor hydrogen-production activities. Here we report a MoNi₄ electrocatalyst supported by MoO₂ cuboids on nickel foam (MoNi₄/MoO₂@Ni), which is constructed by controlling the outward diffusion of nickel atoms on annealing precursor NiMoO₄ cuboids on nickel foam. Experimental and theoretical results confirm that a rapid Tafel-step-decided hydrogen evolution proceeds on MoNi₄ electrocatalyst. As a result, the MoNi₄ electrocatalyst exhibits zero onset overpotential, an overpotential of 15 mV at 10 mA cm⁻² and a low Tafel slope of 30 mV per decade in 1 M potassium hydroxide electrolyte, which are comparable to the results for platinum and superior to those for state-of-the-art platinum-free electrocatalysts. Benefiting from its scalable preparation and stability, the MoNi₄ electrocatalyst is promising for practical water-alkali electrolysers.

In water-alkali electrolyzers, sluggish water dissociation kinetics on platinum-free electrocatalysts result in poor hydrogen-production activities. Here the authors report a MoNi₄ electrocatalyst which reduces the kinetic energy barrier of water dissociation, leading to improved hydrogen-production performance.

Towards Versatile and Sustainable Hydrogen Production through Electrocatalytic Water Splitting: Electrolyte Engineering

Recent advances in power generation from renewable resources necessitate conversion of electricity to chemicals and fuels in an efficient manner. Electrocatalytic water splitting is one of the most powerful and widespread technologies. The development of highly efficient, inexpensive, flexible, and versatile water electrolysis devices is desired. This review discusses the significance and impact of the electrolyte on electrocatalytic performance. Depending on the circumstances under which the water splitting reaction is conducted, the required solution conditions, such as the identity and molarity of ions, may significantly differ. Quantitative understanding of such electrolyte properties on electrolysis performance is effective to facilitate the development of efficient electrocatalytic systems. The electrolyte can directly participate in reaction schemes (kinetics), affect electrode stability, and/or indirectly impact the performance by influencing the concentration overpotential (mass transport). This review aims to guide fine-tuning of the electrolyte properties, or electrolyte engineering, for (photo)electrochemical water splitting reactions.

Non-Noble Metal-based Carbon Composites in Hydrogen Evolution Reaction: Fundamentals to Applications

Hydrogen has been hailed as a clean and sustainable alternative to finite fossil fuels in many energy systems. Water splitting is an important method for hydrogen production in high purity and large quantities. To accelerate the hydrogen evolution reaction (HER) rate, it is highly necessary to develop high efficiency catalysts and to select a proper electrolyte. Herein, the performances of non-noble metal-based carbon composites under various pH values (acid, alkaline and neutral media) for HER in terms of catalyst synthesis, structure and molecular design are systematically discussed. A detailed analysis of the structure-activity-pH correlations in the HER process gives an insight on the origin of the pH-dependence for HER, and provide guidance for future HER mechanism studies on non-noble metal-based carbon composites. Furthermore, this Review gives a fresh impetus to rational design of high-performance noble-metal-free composites catalysts and guide researchers to employ the established electrocatalysts in proper water electrolysis technologies.

Dominating Role of Ni0 on the Interface of Ni/NiO for Enhanced Hydrogen Evolution Reaction

The research of a robust catalytic system based on single NiO_x electrocatalyst for hydrogen evolution reaction (HER) remains a huge challenge. Particularly, the factors that dominate the catalytic properties of NiO_x-based hybrids for HER have not been clearly demonstrated. Herein, a convenient protocol for the fabrication of NiO_x@bamboo-like carbon nanotube hybrids (NiO_x@BCNTs) is designed. The hybrids exhibit superb catalytic ability and considerable durability in alkaline solution. A benchmark HER current density of 10 mA cm^-2 has been achieved at an overpotential of ∼79 mV. In combination with the experimental results and density functional theory (DFT) calculations, this for the first time definitely validates that the inherent high Ni⁰ ratio and the Ni⁰ on the interface of Ni/NiO play a vital role in the outstanding catalytic performance. Especially, the Ni⁰ on the interface of Ni/NiO performs superior activity for water splitting compared with that of bulk Ni⁰. These conclusions provide guidance for the rational design of the future non-noble metallic catalysts.

Ni3Co/G alloy as an earth-abundant robust and stable electrocatalyst for the hydrogen evolution reaction

Nickel-rich nickel–cobalt–graphene alloy was fabricated with outstanding catalytic activity and stability towards HER in alkaline media.

High-efficiency electrochemical hydrogen evolution based on the intermetallic Pt2Si compound prepared by magnetron-sputtering

An intermetallic Pt₂Si compound was prepared by magnetron sputtering, which exhibited higher HER activity than that of Pt in acidic solution.

One-Step Synthesis of a Self-Supported Copper Phosphide Nanobush for Overall Water Splitting

Developing cheap, stable, and efficient electrocatalysts is of extreme importance in the effort to replace noble metal electrocatalysts for use in the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). We report a three-dimensional self-supported Cu3P nanobush (NB) catalyst directly grown on a copper mesh via a one-step method. This nanostructure exhibits a superior catalytic activity of achieving a current density of 10 mA cm-2 at 120 mV and exhibits a long-term stability in acid solutions. It shows a Tafel slope of 72 mV dec-1 and an onset potential of -44 mV. This catalyst displays a good catalytic activity in basic electrolytes, reaching a current density of 10 mA cm-2 at the overpotential values of 252 and 380 mV for HER and OER, respectively. The bifunctional Cu3P NB/Cu catalyst exhibits better catalytic performances than the Pt/C and IrO2 catalysts in a two-electrode electrolyzer for overall water splitting.

Energy and fuels from electrochemical interfaces

Advances in electrocatalysis at solid-liquid interfaces are vital for driving the technological innovations that are needed to deliver reliable, affordable and environmentally friendly energy. Here, we highlight the key achievements in the development of new materials for efficient hydrogen and oxygen production in electrolysers and, in reverse, their use in fuel cells. A key issue addressed here is the degree to which the fundamental understanding of the synergy between covalent and non-covalent interactions can form the basis for any predictive ability in tailor-making real-world catalysts. Common descriptors such as the substrate-hydroxide binding energy and the interactions in the double layer between hydroxide-oxides and H---OH are found to control individual parts of the hydrogen and oxygen electrochemistry that govern the efficiency of water-based energy conversion and storage systems. Links between aqueous- and organic-based environments are also established, encouraging the 'fuel cell' and 'battery' communities to move forward together.

Ultramicroelectrode Studies of Self-Terminated Nickel Electrodeposition and Nickel Hydroxide Formation upon Water Reduction

The interaction between electrodeposition of Ni and electrolyte breakdown, namely the hydrogen evolution reaction (HER) via H₃O⁺ and H₂O reduction, was investigated under well-defined mass transport conditions using ultramicroelectrodes (UME's) coupled with optical imaging, generation/collection scanning electrochemical microscopy (G/C-SECM), and preliminary microscale pH measurements. For 5 mmol/L NiCl₂ + 0.1 mol/L NaCl, pH 3.0, electrolytes, the voltammetric current at modest overpotentials, i.e., between -0.6 V and -1.4 V vs. Ag/AgCl, was distributed between metal deposition and H₃O⁺ reduction, with both reactions reaching mass transport limited current values. At more negative potentials, an unusual sharp current spike appeared upon the onset of H₂O reduction that was accompanied by a transient increase in H₂ production. The peak potential of the current spike was a function of both [Ni(H₂O)₆]²⁺_(aq) concentration and pH. The sharp rise in current was ascribed to the onset of autocatalytic H₂O reduction, where electrochemically generated OH^- species induce heterogeneous nucleation of Ni(OH)_2(ads) islands, the perimeter of which is reportedly active for H₂O reduction. As the layer coalesces, further metal deposition is quenched while H₂O reduction continues albeit at a decreased rate as fewer of the most reactive sites, e.g., Ni/Ni(OH)₂ island edges, are available. At potentials below -1.5 V vs. Ag/AgCl, H₂O reduction is accelerated, leading to homogeneous precipitation of bulk Ni(OH)₂·xH₂O within the nearly hemispherical diffusion layer of the UME.

A Perovskite Electrocatalyst for Efficient Hydrogen Evolution Reaction

Perovskite oxides are demonstrated for the first time as efficient electrocatalysts for the hydrogen evolution reaction (HER) in alkaline solutions. A-site praseodymium-doped Pr0.5 (Ba0.5 Sr0.5 )0.5 Co0.8 Fe0.2 O3- δ (Pr0.5BSCF) exhibits dramatically enhanced HER activity and stability compared to Ba0.5 Sr0.5 Co0.8 Fe0.2 O3- δ (BSCF), superior to many well-developed bulk/nanosized nonprecious electrocatalysts. The improved HER performance originates from the modified surface electronic structures and properties of Pr0.5BSCF induced by the Pr-doping.

Design of active and stable Co-Mo-Sx chalcogels as pH-universal catalysts for the hydrogen evolution reaction

Three of the fundamental catalytic limitations that have plagued the electrochemical production of hydrogen for decades still remain: low efficiency, short lifetime of catalysts and a lack of low-cost materials. Here, we address these three challenges by establishing and exploring an intimate functional link between the reactivity and stability of crystalline (CoS2 and MoS2) and amorphous (CoSx and MoSx) hydrogen evolution catalysts. We propose that Co(2+) and Mo(4+) centres promote the initial discharge of water (alkaline solutions) or hydronium ions (acid solutions). We establish that although CoSx materials are more active than MoSx they are also less stable, suggesting that the active sites are defects formed after dissolution of Co and Mo cations. By combining the higher activity of CoSx building blocks with the higher stability of MoSx units into a compact and robust CoMoSx chalcogel structure, we are able to design a low-cost alternative to noble metal catalysts for efficient electrocatalytic production of hydrogen in both alkaline and acidic environments.

Nickel sulfides for electrocatalytic hydrogen evolution under alkaline conditions: a case study of crystalline NiS, NiS2, and Ni3S2 nanoparticles

Electrocatalytic water splitting to produce H₂ plays an important role in the capture, conversion, and storage of renewable energy sources, such as solar energy and wind power.

Nickel cobalt phosphides quasi-hollow nanocubes as an efficient electrocatalyst for hydrogen evolution in alkaline solution

Nickel cobalt phosphides quasi-hollow nanocubes for efficient HER in alkaline solution are synthesized using Ni–Co Prussian blue analogue as templates.

Synthetic advancements and catalytic applications of nickel nitride

This minireview discusses controlled chemical synthetic advancements of nickel nitride and its composites, their fundamental properties, and energy-related applications.

Iron triad (Fe, co, Ni) trinary phosphide nanosheet arrays as high-performance bifunctional electrodes for full water splitting in basic and neutral conditions

A bifunctional electrode consisted of trinary transition-metal phosphide nanosheets on Ni foam has been developed through a facile two-step process.

Direct Observation of Photoinduced Charge Separation in Ruthenium Complex/Ni(OH)2 Nanoparticle Hybrid

Ni(OH)₂ have emerged as important functional materials for solar fuel conversion because of their potential as cost-effective bifunctional catalysts for both hydrogen and oxygen evolution reactions. However, their roles as photocatalysts in the photoinduced charge separation (CS) reactions remain unexplored. In this paper, we investigate the CS dynamics of a newly designed hybrid catalyst by integrating a Ru complex with Ni(OH)₂ nanoparticles (NPs). Using time resolved X-ray absorption spectroscopy (XTA), we directly observed the formation of the reduced Ni metal site (~60 ps), unambiguously demonstrating CS process in the hybrid through ultrafast electron transfer from Ru complex to Ni(OH)₂ NPs. Compared to the ultrafast CS process, the charge recombination in the hybrid is ultraslow (≫50 ns). These results not only suggest the possibility of developing Ni(OH)₂ as solar fuel catalysts, but also represent the first time direct observation of efficient CS in a hybrid catalyst using XTA.

One-step Synthesis of Few-layer WS2 by Pulsed Laser Deposition

Atomically thin tungsten disulfide (WS₂) has attracted much attention in recent years due its indirect-to-direct band gap transition, band gap tunability, and giant spin splitting. However, the fabrication of atomically thin WS₂ remains largely underdeveloped in comparison to its structural analogue MoS₂. Here we report the direct fabrication of highly crystalline few-layer WS₂ on silver substrates by pulse laser deposition at the relatively low temperature of 450 °C. The growth takes places by conventional epitaxy, through the in-situ formation of nearly lattice-matching Ag₂S on the silver surface. Intriguingly, it was observed that the resulting film was composed of not only the usual semiconducting 2H-WS₂ structure but also the less common metallic 1T-WS₂. Modifications of the synthesis parameters allow for control over the crystalline quality, film thickness and crystal phase composition of the resulting WS₂ film.

Ultrathin PdTe nanowires anchoring reduced graphene oxide cathodes for efficient hydrogen evolution reaction

The design and synthesis of efficient electrocatalysts for hydrogen evolution reaction under all pH conditions is extremely desirable but still remains a challenge. Here a facile method to decorate PdTe nanowires on reduced graphene oxide nanosheets (PdTe NWs/rGO) has been developed. As a robust integrated 2D hydrogen-evolving cathode catalyst, the Pd3.02Te NWs/rGO shows a low onset potential of -7 mV and maintains its catalytic activity for at least 48 h in alkaline media. It requires overpotentials (η) of 97 and 355 mV to afford current densities of 10 and 100 mA cm(-2), respectively. The Pd3.02Te NWs/rGO also exhibits a high activity and excellent durability in acidic media.

Co(OH)2 @PANI Hybrid Nanosheets with 3D Networks as High-Performance Electrocatalysts for Hydrogen Evolution Reaction

Hybrid electrocatalysts with excellent electrocatalytic activity for hydrogen reduction are fabricated using an efficient and facile electrochemical route. The electronic and synergistic effects between Co(OH)2 and polyaniline (PANI) in the composite structure are the key factors that generate the high electrocatalytic activity and excellent stability. A highly efficient, non-precious metal-based flexible electrocatalyst for high-performance electrocatalysts is shown, which reveals a novel route for the design and synthesis of electrocatalysts.

Highly active and durable methanol oxidation electrocatalyst based on the synergy of platinum-nickel hydroxide-graphene

Active and durable electrocatalysts for methanol oxidation reaction are of critical importance to the commercial viability of direct methanol fuel cell technology. Unfortunately, current methanol oxidation electrocatalysts fall far short of expectations and suffer from rapid activity degradation. Here we report platinum-nickel hydroxide-graphene ternary hybrids as a possible solution to this long-standing issue. The incorporation of highly defective nickel hydroxide nanostructures is believed to play the decisive role in promoting the dissociative adsorption of water molecules and subsequent oxidative removal of carbonaceous poison on neighbouring platinum sites. As a result, the ternary hybrids exhibit exceptional activity and durability towards efficient methanol oxidation reaction. Under periodic reactivations, the hybrids can endure at least 500,000 s with negligible activity loss, which is, to the best of our knowledge, two to three orders of magnitude longer than all available electrocatalysts.

Metal/Oxide Interface Nanostructures Generated by Surface Segregation for Electrocatalysis

Strong metal/oxide interactions have been acknowledged to play prominent roles in chemical catalysis in the gas phase, but remain as an unexplored area in electrocatalysis in the liquid phase. Utilization of metal/oxide interface structures could generate high performance electrocatalysts for clean energy storage and conversion. However, building highly dispersed nanoscale metal/oxide interfaces on conductive scaffolds remains a significant challenge. Here, we report a novel strategy to create metal/oxide interface nanostructures by growing mixed metal oxide nanoparticles on carbon nanotubes (CNTs) and then selectively promoting migration of one of the metal ions to the surface of the oxide nanoparticles and simultaneous reduction to metal. Employing this strategy, we have synthesized Ni/CeO2 nanointerfaces coupled with CNTs. The Ni/CeO2 interface promotes hydrogen evolution catalysis by facilitating water dissociation and modifying the hydrogen binding energy. The Ni/CeO2-CNT hybrid material exhibits superior activity for hydrogen evolution as a result of synergistic effects including strong metal/oxide interactions, inorganic/carbon coupling, and particle size control.

A Flexible Electrode Based on Iron Phosphide Nanotubes for Overall Water Splitting

The design of cheap and efficient water splitting systems for sustainable hydrogen production has attracted increasing attention. A flexible electrode, based on carbon cloth substrate and iron phosphide nanotubes coated with an iron oxide/phosphate layer, is shown to catalyze overall water splitting. The as-prepared flexible electrode demonstrates remarkable electrocatalytic activity for both the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) at modest overpotentials. The surface iron oxide/phosphate, which is formed in situ, is proposed to improve the HER activity by facilitating the water-dissociation step and serves directly as the catalytically-active component for the OER process.

Insight on Tafel slopes from a microkinetic analysis of aqueous electrocatalysis for energy conversion

Microkinetic analyses of aqueous electrochemistry involving gaseous H2 or O2, i.e., hydrogen evolution reaction (HER), hydrogen oxidation reaction (HOR), oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), are revisited. The Tafel slopes used to evaluate the rate determining steps generally assume extreme coverage of the adsorbed species (θ≈0 or ≈1), although, in practice, the slopes are coverage-dependent. We conducted detailed kinetic analyses describing the coverage-dependent Tafel slopes for the aforementioned reactions. Our careful analyses provide a general benchmark for experimentally observed Tafel slopes that can be assigned to specific rate determining steps. The Tafel analysis is a powerful tool for discussing the rate determining steps involved in electrocatalysis, but our study also demonstrated that overly simplified assumptions led to an inaccurate description of the surface electrocatalysis. Additionally, in many studies, Tafel analyses have been performed in conjunction with the Butler-Volmer equation, where its applicability regarding only electron transfer kinetics is often overlooked. Based on the derived kinetic description of the HER/HOR as an example, the limitation of Butler-Volmer expression in electrocatalysis is also discussed in this report.

Highly porous non-precious bimetallic electrocatalysts for efficient hydrogen evolution

A robust and efficient non-precious metal catalyst for hydrogen evolution reaction is one of the key components for carbon dioxide-free hydrogen production. Here we report that a hierarchical nanoporous copper-titanium bimetallic electrocatalyst is able to produce hydrogen from water under a mild overpotential at more than twice the rate of state-of-the-art carbon-supported platinum catalyst. Although both copper and titanium are known to be poor hydrogen evolution catalysts, the combination of these two elements creates unique copper-copper-titanium hollow sites, which have a hydrogen-binding energy very similar to that of platinum, resulting in an exceptional hydrogen evolution activity. In addition, the hierarchical porosity of the nanoporous copper-titanium catalyst also contributes to its high hydrogen evolution activity, because it provides a large-surface area for electrocatalytic hydrogen evolution, and improves the mass transport properties. Moreover, the catalyst is self-supported, eliminating the overpotential associated with the catalyst/support interface.

Investigations into non-precious metal catalysts for hydrogen evolution are ongoing. Here, the authors report a hierarchical, nanoporous copper-titanium electrocatalyst, and demonstrate that it catalyses hydrogen production at twice the over-all rate of commercial platinum-based catalysts.

Composite Ni/NiO-Cr2O3 Catalyst for Alkaline Hydrogen Evolution Reaction

We report a Ni-Cr/C electrocatalyst with unprecedented mass-activity for the hydrogen evolution reaction (HER) in alkaline electrolyte. The HER kinetics of numerous binary and ternary Ni-alloys and composite Ni/metal-oxide/C samples were evaluated in aqueous 0.1 M KOH electrolyte. The highest HER mass-activity was observed for Ni-Cr materials which exhibit metallic Ni as well as NiO _x and Cr₂O₃ phases as determined by X-ray diffraction (XRD) and X-ray absorption spectroscopy (XAS) analysis. The onset of the HER is significantly improved compared to numerous binary and ternary Ni-alloys, including Ni-Mo materials. It is likely that at adjacent Ni/NiO _x sites, the oxide acts as a sink for OH_ads, while the metallic Ni acts as a sink for the H_ads intermediate of the HER, thus minimizing the high activation energy of hydrogen evolution via water reduction. This is confirmed by in situ XAS studies that show that the synergistic HER enhancement is due to NiO _x content and that the Cr₂O₃ appears to stabilize the composite NiO _x component under HER conditions (where NiO _x would typically be reduced to metallic Ni⁰). Furthermore, in contrast to Pt, the Ni(O _x )/Cr₂O₃ catalyst appears resistant to poisoning by the anion exchange ionomer (AEI), a serious consideration when applied to an anionic polymer electrolyte interface. Furthermore, we report a detailed model of the double layer interface which helps explain the observed ensemble effect in the presence of AEI.

Carbon nitride in energy conversion and storage: recent advances and future prospects

With the explosive growth of energy consumption, the exploration of highly efficient energy conversion and storage devices becomes increasingly important. Fuel cells, supercapacitors, and lithium-ion batteries are among the most promising options. The innovation of these devices mainly resides in the development of high-performance electrode materials and catalysts. Graphitic carbon nitride (g-C3 N4 ), due to structural and chemical properties such as semiconductor optical properties, rich nitrogen content, and tunable porous structure, has drawn considerable attention and shown great potential as an electrode material or catalyst in energy conversion and storage devices. This review covers recent progress in g-C3 N4 -containing systems for fuel cells, electrocatalytic water splitting devices, supercapacitors, and lithium-ion batteries. The corresponding catalytic mechanisms and future research directions in these areas are also discussed.

Carbon-protected bimetallic carbide nanoparticles for a highly efficient alkaline hydrogen evolution reaction

The hydrogen evolution reaction (HER) is one of the two important half reactions in current water-alkali and chlor-alkali electrolyzers. To make this reaction energy-efficient, development of highly active and durable catalytic materials in an alkaline environment is required. Herein we report the synthesis of carbon-coated cobalt-tungsten carbide nanoparticles that have proven to be efficient noble metal-free electrocatalysts for alkaline HER. The catalyst affords a current density of 10 mA cm(-2) at a low overpotential of 73 mV, which is close to that (33 mV) required by Pt/C to obtain the same current density. In addition, this catalyst operates stably at large current densities (>30 mA cm(-1)) for as long as 18 h, and gives nearly 100% Faradaic yield during alkaline HER. The excellent catalytic performance (activity and stability) of this nanocomposite material is attributed to the cooperative effect between nanosized bimetallic carbide and the carbon protection layer outside the metal carbide. The results presented herein offer the exciting possibility of using carbon-armoured metal carbides for an efficient alkaline HER, although pristine metal carbides are not, generally, chemically stable enough under such strong alkaline conditions.

Identification of intrinsic catalytic activity for electrochemical reduction of water molecules to generate hydrogen

Addition of foreign metal onto platinum nearly doubles its reactivity toward water molecule reduction under unbuffered neutral pH conditions.