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Development of cost-effective and highly-efficient bifunctional hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) catalysts is crucial for overall water splitting in practical utilization. Herein, we proposed a novel non-noble metal bifunctional HER/OER electrocatalyst by synergistically coupling a dual-active Co-based heterojunction (Co-CoO) with high conductive and stable two-dimensional Ti3C2-MXene (defined as Co-CoO/Ti3C2-MXene). A series of characterizations and theoretical calculations verify that the synergistic effect of metallic Co with HER activity and CoO with OER performance leads to superb bifunctional catalytic performance, and Ti3C2-MXene can enhance electrical conductivity and prevent the aggregation of the Co-based catalysts, thereby improving both the activity and stability. Co-CoO/Ti3C2-MXene presents low onset potential (ηonset) of 8 mV and Tafel slope of 47 mV·dec−1 for HER (close to that of Pt/C) and ηonset of 196 mV and Tafel slope of 47 mV·dec−1 for OER (superior to that of RuO2). Assembled as an electrolyzer, Co-CoO/Ti3C2-MXene shows a low voltage of 1.55 V at 10 mA·cm−2, high Faradaic efficiency and remarkable stability. It can be driven by a solar cell of ∼ 1.55 V for consecutive production of hydrogen and oxygen gases.

Herein, we present a new strategy for the synthesis of 2D porous MoP/Mo2 N heterojunction nanosheets based on the pyrolysis of 2D [PMo12 O40 ]3- -melamine (PMo12 -MA) nanosheet precursor from a polyethylene glycol (PEG)-mediated assembly route. The heterostructure nanosheets are ca. 20 nm thick and have plentiful pores ( 55 mA cm-2 in neutral medium and >190 mA cm-2 in alkaline medium.

Development of cost-effective, active and durable electrocatalysts for overall water splitting is still a huge challenge. Herein, we have constructed one-dimensional (1D) cobalt sulfide and vanadium sulfide heterojunction nanowires arranged on carbon cloth (Co9S8-V3S4/CC) as bifunctional electrocatalysts for the efficient overall water splitting. The 1D wire-structured Co9S8-V3S4 heterojunctions possess large surface area, plentiful active sites and rapid transport of electrons/reactants and the release of gas. Importantly, the electron transfer from Co9S8 to V3S4 occurs at the interface due to the strong electronic coupling effect in Co9S8-V3S4 heterojunction, in which the electron-attracting V3S4 (V2+) optimizes the adsorption of H* active species for hydrogen evolution reaction (HER), while the electron-losing Co9S8 (Co3+) responds to the enhancement of oxygen evolution reaction (OER) activity. Co9S8-V3S4/CC exhibits low overpotentials of 85 and 232 mV at 10 mA cm−2 and small Tafel slopes of 51 and 59 mV dec−1 for HER and OER, respectively. Especially, the electrolyzer with Co9S8 V3S4/CC as both the anode and cathode requires low onset voltage of 1.35 V and cell voltage of 1.53 V at 10 mA cm−2 and exhibits high Faradaic efficiencies and robust stability. It can be driven by a solar cell (1.53 V) for continuous production of hydrogen and oxygen. This study highlights the design of 1D sulfide heterojunction in pursuit of highly efficient electrocatalysts for overall water splitting.

Convenient high-yield synthesis of metal nitride-based materials with good stability is pursued constantly. Especially considering the advantages of 2D materials, the combination of cobalt nitride with 2D nanosheets is hoped to promote its catalytic ability, but the synthesis remains a challenge. Herein, we showed the feasible synthesis of 2D thin sheets composed of Co5.47N–MgO embedded in carbon (2D Co5.47N–MgO@C sheets) in high yield, which is based on a grinding treatment of Co salt and 2-methylimidazole (2-MIM) in MgCl2/NaCl/KCl salts followed by two-step calcination. During the first nitridation step, 2-MIM, which had already been coordinated with Co and Mg, can convert into an amorphous carbon layer with the embedded Co species, along with the formation of MgO. During the next step, Co5.47N can be generated in tight connection with the amorphous carbon layer and MgO. The molten salt medium can induce the orientated growth of the material and prevent it from agglomeration, even in the case of a high Co concentration, thus realizing the high-yield synthesis and dispersion of the 2D sheets. Remarkably, the present synthetic strategy exhibits high conversion (almost 100%) of the added Co source into cobalt nitride. The reduction of an aromatic nitro compound (4-nitrophenol, 4-NP) into an amine compound (4-aminophenol, 4-AP) was used to evaluate the catalytic performance. 4-NP was effectively converted. The alkalinity of MgO is favourable for the deprotonation of 4-NP, which enhances the activity. Notably, there was no obvious change in performance after recycled use up to 10 times owing to the protection of carbon. Furthermore, tests confirmed that the 2D Co5.47N–MgO@C sheets exhibit excellent catalytic performance for the reduction of a series of nitro compounds. The present method provides a promising route for the convenient synthesis of 2D nanosheet-based catalysts.

Molybdenum phosphide is one of the most potential electrocatalysts for the hydrogen evolution reaction (HER), whereas it is still challenging to achieve an efficient molybdenum phosphide-based catalyst that performs well over a wide pH range. Herein, a porous nanoplate composed of small MoP flakes confined in thin N, P, S-triple-doped carbon (MoP@NPSC) was prepared by the assembly of phosphomolybdic acid (H3PMo12O40·nH2O, {PMo12}) and egg white, followed by phosphorization. Given its small size (ca. 1 nm) in favor of deriving small particles and the oxygen-rich surface with strong coordination ability, the {PMo12} cluster was selected to combine with egg white to obtain a lamellar hybrid precursor via a hydrogen bond. Through controllable phosphating, a nanoplate organized by interconnected MoP particles was generated, accompanied by the in situ formation of the N, P, S-doped carbon thin layer and pores from the pyrolysis of egg white. The plentiful pores, thin carbon coating, and multielement doping bring about promoted electrolyte/bubble diffusion, enhanced conductivity and stability, and lowered adsorption energy of hydrogen/hydroxyl, respectively. All of the above merits endow MoP@NPSC with prominent activity with low overpotentials of 50, 76, and 71 mV at 10 mA cm-2 toward the HER in alkaline, neutral, and acid media, respectively, and nearly no attenuation after 40 h of testing. Especially, compared with commercial Pt/C, MoP@NPSC exhibits similar low onset potential and even better at large current density in 1 M KOH. The electrolyzer equipped with the MoP@NPSC cathode and the NiFe-LDH anode requires only 1.52 V to deliver 10 mA cm-2 and can be powered by a solar cell (1.524 V) charged by sunlight.

Proton exchange membrane water electrolyzer (PEMWE) in acidic media is a hopeful scenario for hydrogen production by using renewable energy sources, but the grand challenge lies in substituting active and stable noble-metal catalysts. Herein, a robust electrocatalyst of V-CoP2 porous nanowires arranged on carbon cloth is successfully fabricated via incorporating vanadium into CoP2 lattice. Structural characterizations and theoretical analysis indicate that lattice expansion of CoP2 caused by V incorporation results in the upshift of d-band center, which is conducive to hydrogen adsorption for boosting HER activity. Besides, V promotes surface reconstruction to generate a thicker Co3O4 layer that enhances acid-corrosion resistance and optimizes the adsorption of water and oxygen-containing species, thus improving OER activity and stability. Accordingly, it presents a superior acidic overall water splitting activity (1.47 V@10 mA cm-2) over Pt-C/CC||RuO2/CC, and remarkable stability. This work proposes a new route to design efficient electrocatalysts via lattice engineering for PEMWE.

The three-dimensional character of carbon nitride can endow it with a larger specific surface area and more catalytic active sites, which are beneficial for charge and mass transfer to enhance photocatalytic hydrogen production reactions. Herein, we reported the direct assembly of three-dimensional structured carbon nitride from the thermal polymerization of 3-amino-1,2,4-triazole (AT) and melamine molecules. The 3D C3N4 consisted of one-dimensional thick tubes with numbers of thin tubes grown uniformly on their surfaces. It was noted that the assembly was decorated with triazole ring groups that generated a special nitrogen-rich structure, further broadening the visible-light response range. Furthermore, the nitrogen-rich carbon nitride had a large surface area of 71 m2 g−1, leading to a significant increase in the number of catalytic active sites. Thus, the photocatalytic hydrogen production rate reached 7.1 mmol g−1 h−1, 11.2 times higher than that of bulk C3N4. This work may provide a new strategy to controllably synthesize three-dimensional carbon nitride assemblies for photocatalytic applications.

The construction of porous bifunctional electrocatalysts is highly desirable for efficient overall water splitting, which however remains a challenge. Herein, porous cobalt/tungsten nitride (Co/WN) polyhedra were successfully synthesized by the growth of a polyhedral Co–W oxide precursor on Ni foam followed by a controlled nitridation as a bifunctional electrocatalyst for high-efficiency hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). The porous structure of the Co/WN polyhedra can provide more reactive sites and promote mass/charge transfer. Moreover, the synergy between Co and WN can adjust the electronic structure, thus facilitating the adsorption/desorption of intermediates on the catalyst. Due to the above advantages, the optimized Co/WN polyhedra exhibit superior bifunctional performance in alkaline electrolyte with low overpotentials of 27 and 232 mV (without iR compensation) at a current density of 10 mA cm−2 for the HER and OER, respectively. Especially, the Co/WN-600 sample shows better performance than commercial Pt/C and RuO2 at high current densities. Furthermore, the self-supported Co/WN polyhedra enable overall water splitting at a low cell voltage of 1.51 V to obtain a current density of 10 mA cm−2 with outstanding catalytic durability.

The photocatalytic efficiency of polymeric carbon nitride is hampered by high carrier recombination rate and low charge transfer. Herein, these issues are addressed by constructing 1D strip-like carbon nitride with a large π-electron conjugated system from carbon-doping, realizing the synchronization control of its electronic structure and morphology. Nicotinic acid, a monomer with the carboxyl group and pyridine ring, and melamine are selected for assembling the strip-like supramolecular via hydrogen bond under hydrothermal process. Both peripheral pyridine unit and hydrogen bond have significant effect on self-assembly process of nicotinic acid and melamine along one dimension to form a strip-like precursor. Subsequently, 1D thin porous strip-like carbon nitride is obtained by calcination treatment of precursor. The as-prepared 1D strip-like carbon nitride with effective π delocalization from carbon-doping and porous structure can accelerate charges and mass transfer and provide extra active sites. Both theoretical and experimental results demonstrate that carbon doping (pyridine heterocycle) narrows the bandgap via manipulating the band position and increases the π electron density. Thus, the 1D porous thin strip-like carbon nitride realizes compelling hydrogen evolution rate (126.2 µmol h-1 ), far beyond (≈18 fold) the value of polymeric carbon nitride (PCN) (7.2 µmol h-1 ) under visible light irradiation.

The direct formic acid fuel cell (DFAFC) has received increasing attention in the sustainable and clean energy field. However, the high cost, poor durability, and shortage of palladium (Pd) based catalysts for the formic acid oxidation reaction (FAOR) restrict the large-scale application of DFAFC. Herein, molybdenum nitride/reduced graphene oxide (Mo2N/rGO) was designed as an effective cocatalyst of Pd for FAOR based on an assembly-immobilization method. It is shown that the small-sized Mo2N is well dispersed on rGO with high density, which is favorable for the post-loading deposition of Pd onto the rGO to form a strongly coupled Pd–Mo2N structure. The strong interaction between Pd and Mo2N, verified by a series of characterizations, is helpful for promoting the performance of Pd. Electrochemical tests indicate that the Pd–Mo2N/rGO catalyst shows superior activity to other Pd based catalysts, with a current density of 532.7 mA mgPd−1, which is 1.7 and 2.2 times greater than those of Pd/reduced graphene oxide (Pd/rGO) and Pd/Vulcan XC-72 (Pd/VC), respectively. In addition, Pd–Mo2N/rGO exhibits enhanced CO tolerance and good stability. The good performance is mainly ascribed to the intimate contact between Mo2N and Pd which gives enhanced synergistic action. The excellent performance of Pd–Mo2N/rGO makes it a potential electrocatalyst for DFAFC applications.

The development of effective and low-cost catalysts for overall water splitting is essential for clean production of hydrogen from water. In this paper, we report the synthesis of cobalt-vanadium (Co-V) bimetal-based catalysts for the effective water splitting. The Co2V2O7· x H2O nanoplates containing both Co and V elements were selected as the precursors. After the calcination under NH3 atmosphere, the Co2VO4 and Co/VN could be obtained just by tuning the calcination temperature. Electrochemical tests indicated that the Co-V bimetal-based materials could be used as active hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) catalyst by regulating their structure. The Co/VN showed good performance for HER with the onset potential of 68 mV and can achieve a current density of 10 mA cm−2 at an overpotential of 92 mV . Meanwhile, the Co2VO4 exhibited the obvious OER performance with overpotential of 300 mV to achieve a current density of 10 mA cm−2. When the Co2VO4 and Co/VN were used as the anode and cathode in a two-electrode system, respectively, the cell needed a voltage of 1.65 V to achieve 10 mA cm−2 together with good stability. This work would be indicative to constructing Co-V bimetal-based catalysts for the catalytic application.

Cu2ZnSnS4 (CZTS) and Cu2ZnSn(S,Se)4 (CZTSSe) as promising photovoltaic materials have drawn much attention because they are environmentally benign and earth-abundant elements. In this work, the monodispersed, low-cost Cu2ZnSnS4 nanocrystals with small size have been controllably synthesized via a wet chemical routine. And CZTSSe could be easily prepared after selenization of CZTS. When they are employed as counter electrodes (CEs) for dye-sensitized solar cells (DSSCs), the power conversion efficiency (PCE) has been improved from 3.54% to 7.13% as CZTS is converted to CZTSSe, which is also compared to that of Pt (7.62%). The exact reason for the enhanced catalytic activity of I3– is discussed with the work function and density functional theory (DFT) when CZTSSe converted from CZTS. The results of a Kelvin probe suggest that the work function of CZTSSe (5.61 eV) is closer to that of Pt (5.65 eV) and higher than that of CZTS, which matched the redox shuttle potential better. According to the theory calcula...

The development of effective catalysts for the catalytic conversion of the harmful nitrophenol (NP) into the useful aminophenol (AP) has received extensive interest. Herein, we report the easy and large-scale synthesis of strongly coupled Ag/TiO2 heterojunctions based on the coordinated action of organic components with a multi-kind metal precursor. The heterojunctions were effective and stable catalysts for the photothermal catalytic reduction of 4-NP to 4-AP. In the synthesis, critic acid, ethylene glycol, AgNO3, and tetrabutyl titanate were dissolved and coordinated in water. Under heating, a precursor gel having a uniform distribution of Ag and Ti was gradually formed. Via calcination in air, the Ti precursor was transformed into TiO2, accompanied by the reduction of Ag+ to Ag nanoparticles. The formation of Ag/TiO2 composites with intimate interface contact benefited from the uniform distribution of different components in the precursor gel. The Ag/TiO2 functioned as an effective catalyst for the reduction of 4-NP, exhibiting higher activity than the many reported Ag-based catalysts. The catalytic reaction over Ag/TiO2 had a small t 0 with good activity and reuse performance. After 10 cycles of reuse, the conversion efficiency exhibited no obvious change. Importantly, the conversion of 4-NP was significantly enhanced under light irradiation provided by a 150-W Xe lamp (the visible light from cutoff have equal function), but ultraviolet light did not promote the conversion. The conversion time was reduced from 620 to 270 s with light irradiation (15 °C). The reaction rate under light irradiation (0.014 s−1) was approximately three times higher than that in the dark at 15 °C (0.0044 s−1) and even better than that in the dark at 25 °C (0.01 s−1). A series of experiments indicated that the light irradiation promoted the conversion of 4-NP because of the localized surface plasmon resonance effect of Ag, which generated hot e− and h+ particles and local heating around the particles via their absorption of the light.

The excellent photocatalytic performance of a commercial ZnO (C-ZnO-1) was demonstrated. This ZnO showed approximately 3.8, 7.4 and 5.2 times greater activity than P25 TiO 2 for the degradation of rhodamine B, methyl orange and methyl blue, respectively. After compounding with Ag, the catalyst showed record-high activities for the degradation of the three dyes (approximately 9.5, 13, and 50 times that of P25). The high activity of C-ZnO-1 is attributed to the low concentration of bulk defects (i.e., a high degree of crystallinity) and the relatively high number of surface defects (i.e., a higher ratio of surface hydroxyl oxygen).

The visible-light driven, Pt-free photocatalytic H2 evolution (PHE) is promising for clean and sustainable H2 production. The construction of the heterojunction structure with intimate contact and good light adsorption ability is important for realizing the high effective PHE. Here, the core-shell structured MoS2/CdS hybrids were constructed through “sequential two-step hydrothermal growth” route for Pt-free PHE. In the synthesis, the hierarchical flower-like MoS2 was firstly obtained through the reaction of ammonium molybdate and excessive thiourea. Subsequently, without need of centrifugation, the cadmium acetate (Cd source) was added into the cooled MoS2 solution directly followed by a secondary hydrothermal reaction. In the process, the Cd2+ could react with partially S2− in MoS2 (substituted reaction) and with the excessive S2− ions in solution to generate CdS, resulting in the formation of CdS shell contacted with MoS2 core. The micro-structure of the composites (such as the thickness and morphology of CdS shell) could be tuned by changing the amount of Mo source and Cd source. In the composites, the CdS on the outside is convenient to absorb the solar light. The intimate contact of CdS and MoS2 is beneficial to charge transfer. As a result, the MoS2/CdS catalyst showed high catalytic activity for PHE under visible light irradiation (λ > 420 nm). The H2 evolution rate could reach to 775 μmol h−1 (20 mg catalyst), which is much higher than pure CdS (12 μmol h−1) and Pt-CdS (64 μmol h−1). The good activity should be related with CdS outside shell beneficial for light adsorption and intimate contact of CdS and MoS2 for easy charge transfer. A series of experiments demonstrate that the formation of the heterojunction can effectively enhance the charge transfer ability and retard the recombination of electron-hole pairs, thus improving PHE activity and alleviating the photocorrosion of CdS component.

The construction of noble metal-oxide nanocrystal hybrids (MOHs) with good interface contact, broadly tunable composition and high yield is critical for their application in the advanced fields. In this paper, a general route was developed for constructing MOHs with intimate interfacial contact based on the coordination of an organic agent with multiple kinds of metal precursors. In the synthesis, critic acid, desirable sources for metal nanoparticles (NPs; for example, Ag+ salts), oxides (for example, Zn2+ salts) and ethylene glycol were dissolved in water. After heating at low temperature to produce the precursor gels and subsequent calcination under air, one kind of the ions (Zn2+) was transformed into an oxide (ZnO) in company with the reduction of another ion (Ag+) to generate metal NPs (Ag). Benefitting from the uniform distribution of Ag and Zn precursor in the gels, the Ag/ZnO composites with good interface contact were finally formed. The Ag/ZnO hybrids can be used as effective catalysts for the catalytic reduction of p-nitrophenol and photocatalytic degradation of pollutants. Under optimized conditions, the Ag/ZnO showed a rate approximately 1.5 times higher than that of Degussa P25 TiO2 for the degradation of rhodamine B. The OH· radicals and ·O2 − play predominant roles in the photocatalytic reaction. The Ag/ZnO can also act as an effective catalyst for the reduction of p-nitrophenol with good reuse performance. The present route is also suitable to construct MOHs with other components (Pt/TiO2, Pt/ZnO, etc.). The route is promising to produce MOHs due to the virtues of the easy synthesis process and high yields.

Cu2O is widely used in the visible-light photocatalytic field, but its photocatalytic activity and stability still need to be further enhanced. Thus, searching for an efficient method to inhibit photocorrosion of Cu2O and boost its photogenerated charge carriers’ separation is very important and challenging. Herein, Cu2O@CuS core-shell hexapetalous flowers were synthesized by hydrothermal and in-situ chemical vapor deposition (CVD) strategy. The Cu2O hexapetalous flowers were firstly obtained through hydrothermal procedure, and then CuS in-situ grew on Cu2O to form core-shell structure by CVD, which effectively inhibited the photocorrosion of Cu2O. Meanwhile, Cu2O@CuS core-shell structure could extend their light absorption ranges from 200 to 1500 nm; promote the separation of electrons and holes in photocatalytic system. Thus, under the wide-spectral region, Cu2O@CuS exhibited excellent photocatalytic performance for the degradation of tetracycline at 91% with good cycling ability, resulting from the effective separation of photogenerated charges, more free radicals such as OH and O2−, increases of utilization rate of visible-light. These results indicate that in-situ CVD strategy is a feasible method to improve visible-light photocatalytic activity and stability of Cu2O.

Simultaneous highly efficient production of hydrogen and conversion of biomass into value-added products is meaningful but challenging. Herein, a porous nanospindle composed of carbon-encapsulated MoO2 -FeP heterojunction (MoO2 -FeP@C) is proposed as a robust bifunctional electrocatalyst for hydrogen evolution reaction (HER) and biomass electrooxidation reaction (BEOR). X-ray photoelectron spectroscopy analysis and theoretical calculations confirm the electron transfer from MoO2 to FeP at the interfaces, where electron accumulation on FeP favors the optimization of H2 O and H* absorption energies for HER, whereas hole accumulation on MoO2 is responsible for improving the BEOR activity. Thanks to its interfacial electronic structure, MoO2 -FeP@C exhibits excellent HER activity with an overpotential of 103 mV at 10 mA cm-2 and a Tafel slope of 48 mV dec-1 . Meanwhile, when 5-hydroxymethylfurfural is chosen as the biomass for BEOR, the conversion is almost 100%, and 2,5-furandicarboxylic acid (FDCA) is obtained with the selectivity of 98.6%. The electrolyzer employing MoO2 -FeP@C for cathodic H2 and anodic FDCA production requires only a low voltage of 1.486 V at 10 mA cm-2 and can be powered by a solar cell (output voltage: 1.45 V). Additionally, other BEORs coupled with HER catalyzed by MoO2 -FeP@C also have excellent catalytic performance, implying their good versatility.

A low-cost catalyst for the hydrogen evolution reaction (HER) over a broad pH range is highly desired to meet the practical needs in different areas. In this study, hierarchical flower-like MoS2@MoP core-shell heterojunctions (HF-MoSP) are designed as a promising catalyst for HER over a broad pH range. The materials are obtained by the controllable phosphidation of the hierarchical MoS2 flower (HF-MoS2) composed of thin silk belt-like sheets. The phosphidation degree, P/S ratio and work function (WF) of HF-MoSP can be tuned easily over broad range by changing the phosphidation temperature. Under optimized condition, HF-MoSP exhibits excellent electrocatalytic activity for HER with a low onset overpotential of 29 mV and η of 108 mV at 10 mA cm(-2) in 0.5 M H2SO4 and retains its good activity for 30 h. In addition, the catalyst shows excellent activity in 1 M KOH with an onset overpotential of 42 mV and η of 119 mV at 10 mA cm(-2). The catalysts also exhibit obvious activity in neutral, weak acid and weak alkaline conditions. The good performance is relative to the synergy of the MoP shell and MoS2 core and the high WF of HF-MoSP close to Pt, and the large SBET of HF-MoSP benefited from the hierarchical structure. This study represents the construction of the core-shell heterojunction and provides a new way to provide the low-cost and high-performance catalyst for HER.

A effective “1-methylimidazole (1-MD)-fixation” strategy was developed to anchor small-sized nitrides on carbon supports. The carbon supports used (CNTs (carbon nanotubes), carbon black, reduced graphene oxides) and nitrides (WN, Mo2N) can be easily tuned. The application of the nitride/CNT hybrids as non-Pt catalysts for the hydrogen evolution reaction (HER) was also demonstrated. It was shown that the performance could be tuned by the kind of the nitride. The combination of WN and Mo2N simultaneously on CNTs can improve the HER performance obviously. It is expected that the present “fixation” route could be useful to anchor small-sized nitrides on carbon supports for application in electrocatalytic fields.

Cluster-like molybdenum phosphide particles were anchored on reduced graphene oxide (MoP/rGO) with high uniformity by using phosphomolybdic acid as a molybdenum precursor based on a robust assembly-immobilization method. Benefiting from the small size, and even distribution of the MoP particles, the MoP/rGO hybrid exhibits superior electrocatalytic activity towards the hydrogen evolution reaction both in acidic and alkaline media.

Layer-like nanocarbons with high surface area and good conductivity are promising materials for supercapacitors due to their good ability for effective charge-transfer and mass-transfer. In this paper, stacked layer-like porous carbon containing RGO (reduced graphene oxides) (LPCG) was constructed via the GO-induced assembly of gelatin followed by carbonization and activation processes. Under suitable conditions, LPCG-based materials with a thickness of about 100 nm and a high specific surface area (up to 1476 m(2) g(-1)) could be obtained. In the materials, the closed combination of RGO and porous carbon can be observed, which is favourable for the development of the synergistic effects of both components. The presence of GO can not only enhance the conductivity of LPCG-based materials, but also is essential for the formation of a thin carbon sheet with a stacked structure. Otherwise, the plate-like, non-stacked carbon with a thickness of about 500 nm could be formed in the absence of RGO. The porous structure along with the presence of RGO allows rapid charge-transfer and easy access and diffusion of electrolyte ions. As a result, the materials exhibited a high discharge specific capacitance (455 F g(-1) at 0.5 A g(-1), 366 F g(-1) at 1 A g(-1)), good rate capability (221 F g(-1) at density 30 A g(-1)) and good cycling stability. In aqueous electrolytes, the energy density could be up to 9.32 W h kg(-1) at a relatively low power density of 500 W kg(-1) with a good cycling stability (>96% over 5000 cycles). It was found that (1) the rational combination of RGO and porous carbon is essential for enhancing the capacitance performance and improving the cycling stability and (2) the high conductivity is favorable for improving the rate performance of the materials. The LPCG-based materials have extensive potential for practical applications in energy storage and conversion devices.

An in situ catalytic etching strategy is developed to fabricate holey reduced graphene oxide along with simultaneous coupling with a small-sized Mo2 N-Mo2 C heterojunction (Mo2 N-Mo2 C/HGr). The method includes the first immobilization of H3 PMo12 O40 (PMo12 ) clusters on graphite oxide (GO), followed by calcination in air and NH3 to form Mo2 N-Mo2 C/HGr. PMo12 not only acts as the Mo heterojunction source, but also provides the Mo species that can in situ catalyze the decomposition of adjacent reduced GO to form HGr, while the released gas (CO) and introduced NH3 simultaneously react with the Mo species to form an Mo2 N-Mo2 C heterojunction on HGr. The hybrid exhibits superior activity towards the hydrogen evolution reaction with low onset potentials of 11 mV (0.5 m H2 SO4 ) and 18 mV (1 m KOH) as well as remarkable stability. The activity in alkaline media is also superior to Pt/C at large current densities (>88 mA cm-2 ). The good activity of Mo2 N-Mo2 C/HGr is ascribed to its small size, the heterojunction of Mo2 N-Mo2 C, and the good charge/mass-transfer ability of HGr, as supported by a series of experiments and theoretical calculations.