We report superior hydrogen evolution activity of metal-free borocarbonitride (BCN) catalysts.

Generation of hydrogen by photochemical, electrochemical, and other means is a vital area of research today, and a variety of materials have been explored as catalysts for this purpose. CN, MoS, and nitrogenated RGO (NRGO) are some of the important catalytic materials investigated for the hydrogen evolution reaction (HER) reaction, but the observed catalytic activities are somewhat marginal. Prompted by preliminary reports that covalent cross-linking of 2D materials to generate heteroassemblies or nanocomposites may have beneficial effect on the catalytic activity, we have synthesized nanocomposites wherein CN is covalently bonded to MoS or NRGO nanosheets. The photochemical HER activity of the CN-MoS nanocomposite is found to be remarkable with an activity of 12778 μmol h g and a turnover frequency of 2.35 h. The physical mixture of CN and MoS, on the other hand, does not exhibit notable catalytic activity. Encouraged by this result, we have studied electrochemical HER activity of these composites as well. CN-MoS shows superior activity relative to a physical mixture of MoS and CN. Density functional theory calculations have been carried out to understand the HER activity of the nanocomposites. Charge-transfer between the components and greater planarity of cross-linked layers are important causes of the superior catalytic activity of the nanocomposites. Covalent linking of such 2D materials appears to be a worthwhile strategy for catalysis and other applications.

Hydrogen generation by water splitting is clearly a predominant and essential strategy to tackle the problems related to renewable energy. In this context, the discovery of proper catalysts for electrochemical and photochemical water splitting assumes great importance. There is also a serious intent to eliminate platinum and other noble metal catalysts. To replace Pt by a non‐metallic catalyst with desirable characteristics is a challenge. Borocarbonitrides, (BxCyNz) which constitutes a new class of 2D material, offer great promise as non‐metallic catalysts because of the easy tunability of bandgap, surface area, and other electronic properties with variation in composition. Recently, BxCyNz composites with excellent electrochemical and photochemical hydrogen generation activities have been found, especially noteworthy being the observation that BxCyNz with a carbon‐rich composition or its nanocomposites with MoS2 come close to Pt in electrocatalytic properties, showing equally good photochemical activity.

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/cm 2 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.hydrogen evolution reaction | dual-pulse plating | nickel/nickel hydroxide interface | graphite rod electrode T o render electrochemical generation of H 2 from water ecofriendly, we could use electricity from solar photovoltaic devices. A major limitation would still be the use of Pt as the catalyst. In the last few years, there has been great interest in replacing Pt by inexpensive, readily available catalysts. Several catalysts have been studied in recent times for the electrochemical hydrogen evolution reaction (HER) including transition metal-based heterostructures (1-6) and certain metal-free catalysts (7-11). Of these, Ni-based catalysts such as Ni 2 P (12, 13), NiFeP (14), NiFe layered double hydroxide (15-17), and Ni/ NiO/carbon nanotube (18) seem to be more promising for water splitting. It has been shown recently that activation of a Nicarbon-based catalyst through the application of an electrochemical potential results in HER activity comparable to Pt in acidic medium (6). We have been investigating the use of Ni along with Ni(OH) 2 as a potential catalyst for the purpose, since Ni(OH) 2 clusters with Pt and other transition metals (19-23) generally exhibit good HER activity and Ni itself is only next to Pt in activity. With this purpose, we have used the dualpulse-plating (PP) method (24) to generate the Ni/Ni(OH) 2 interface embedded in graphene sheets on a graphite electrode. Amazingly, the Ni/Ni(OH) 2 /graphite electrode prepared by us gives a current density of ∼200 mA/cm 2 [at −0.30 V vs. reversible hydrogen electrode (RHE)] and an overpotential of ∼190 mV required to sustain a current density of 20 mA/cm 2 over long periods. For a current density of 200 mA/cm 2 , this electrode beats the activity of the Pt wire by a factor of ∼1.5 in terms of the overpotential.The outstanding performance of the Ni/Ni(OH) 2 /graphite electrode is due to the dual-PP method adopted by us to give rise to colloidal hydroxide inclusions in the electrodeposits (25-30) (Methods). While fabricating the Ni/Ni(OH) 2 interface, the galvanostatic pulses shift the cathodic potential in the negative direction to such an extent that the ensuing water splitting yielding hydrogen is followed by the simultaneous incorporati...

Hydrogen production by photochemical and electrochemical means is an important area of research related to renewable energy. 2D nanomaterials such as C 3 N 4 and MoS 2 have proven to be active for the hydrogen evolution reaction (HER). Phosphorene, a mono-elemental 2D layer of phosphorus, is known to catalyze the HER, but the activity is marginal. The use of phosphorene is also limited by its ambient instability. We have been able to prepare covalently cross-linked nanocomposites of phosphorene with MoS 2 as well as MoSe 2 . The phosphorene− MoS 2 nanocomposite shows excellent photochemical HER activity yielding 26.8 mmol h −1 g −1 of H 2 , while only a negligible amount is produced by the physical mixture of phosphorene and MoS 2 . The phosphorene−MoS 2 composite also displays high electrochemical HER activity with an onset overpotential of 110 mV, close to that of Pt. The enhanced HER activity of the phosphorene−MoS 2 nanocomposite can be attributed to the ordered cross-linking of the 2D sheets, increasing the interfacial area as well as the charge-transfer interaction between phosphorene and MoS 2 layers. The phosphorene−MoSe 2 nanocomposite also exhibits good photochemical HER activity.