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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.

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.

Exploring inexpensive and efficient electrocatalysts for the hydrogen evolution reaction (HER) in a wide pH range is crucial for the development of sustainable energy applications. Herein, a novel 3D hierarchical V–Ni-based nitride heterojunction on carbon cloth (VN@Ni3N–Ni/CC) was designed and fabricated as a promising pH-universal HER electrocatalyst through the controllable nitridation of the corresponding V–Ni–O/CC precursor. A series of experimental parameters were tested to adjust the nanostructure of the material and to gain insight into the relationship between its structure and activity. The VN@Ni3N–Ni/CC sample produced under optimized conditions showed excellent catalytic activity and stability over a wide pH range with onset potentials of 8, 23 and 32 mV and Tafel slopes of 40, 97 and 79 mV dec−1 in 1.0 M KOH, 1.0 M PBS and 0.5 M H2SO4 electrolytes, respectively. Notably, with regards to catalytic activity, our VN@Ni3N–Ni/CC sample outperformed most currently available non-noble metal catalysts, and was also found to be superior to Pt–C/CC at certain current density intervals in alkaline and neutral media. The outstanding performance of VN@Ni3N–Ni/CC was mainly attributed to the highly active heterointerfaces, excellent electronic conductivity and facilitated mass transport of its 3D hierarchical framework. We expect the results of this work to help in the design and engineering of other heterojunction materials based on hybrids of early- and late-transition metals, and hence yield materials that may be used as highly efficient catalysts for various applications.

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.

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.