Transition metal phosphides (TMPs) are expected to be excellent electrocatalysts for oxygen evolution reaction (OER) because of their high stability, highly conducting metalloid nature, highly abundant constituting elements, and the ability to act as a precatalyst due to in situ surface-formed oxy-hydroxide species. Herein, a "one-pot" colloidal approach has been used to develop a rod-shaped one-dimensional non-noble metal FeCoP electrocatalyst, which exhibits an excellent OER activity with an exceptionally high current density of 950 mA cm −2 , a turnover frequency value of 7.43 s −1 , and a low Tafel slope value of 54 mV dec −1 . The FeCoP electrocatalyst affords OER ultralow overpotentials of 230 and 260 mV at current densities of 50 and 100 mA cm −2 , respectively, in 1.0 M KOH, and demonstrates a superior catalytic stability of 10,000 cycles and durability up to 60 h at 50 mA cm −2 . An insight into the superior and stable electrocatalytic OER performance by the FeCoP nanorods is obtained by extensive Xray photoelectron spectroscopy, X-ray diffraction, Raman and infrared spectroscopy, and cyclic voltammetry analyses for a mechanistic study. This reveals that a high number of electrocatalytically active sites enhance the oxygen evolution and kinetics by offering metal ion sites for utilitarian in situ surface formation and adsorption of *O, *OH, and *OOH reactive species for OER catalysis.

Energy conversion and energy storage are two crucial challenges in green chemistry that have attracted tremendous attention for the last several decades. In this work, we have addressed both issues by synthesizing nitrogen-rich, few-layer-thick holey graphitic carbon nitride (g-C3N4) nanosheets by a simple, novel, direct thermal polymerization method, which is found to be very good in photocatalytic H2 evolution reaction (energy-conversion) and charge-storage supercapacitor (energy-storage) applications. This as-synthesized conjugated polymer semiconductor (obtained stoichiometry C3N4.8) with unique structural and morphological advantages exhibits superior photocatalytic water splitting activity to H2 evolution (2 620 μmol h–1 g–1) without the help of any cocatalysts under visible light in the presence of 20% triethanolamine (TEOA). The calculated apparent quantum yield is 8.5% at 427 nm, and the rate of photocatalytic hydrogen generation remained constant for nine consecutive catalytic cycles (9 h photocatalysis). The present material also shows electrochemical double layer capacitor (EDLC) behavior in alkaline electrolyte, where a symmetric coin cell device consisting of this electrode material without any large area support or conductive filler delivers high specific capacitance (275 F g–1), energy density (30 Wh kg–1), and power density (6651 W kg–1), and the supercapacitor cell can retain >98% capacitance efficiency up to 10 000 measured cycles at various current densities.

In the field of photocatalysis, metal–organic frameworks (MOFs) have emerged as potential photocatalysts owing to their well-defined and tailorable porous structures, high surface areas, and inherent semiconductor-like behavior. However, their photocatalytic H2 evolution reaction is still limited due to the higher charge recombination rates. Precious metal cocatalysts, such as Pt and Au, are used to suppress electron–hole recombination effects by forming a Schottky junction, but the high cost and scarcity of these metals limit their large-scale applications. Herein, for the first time, we have developed novel ZnCo-MOF hollow rings at room temperature and loaded it with monodispersed transition-metal phosphide (TMPs; NiCoP, FeCoP, Ni2P, CoP) nanoparticles as non-noble-metal cocatalysts for efficient visible light driven H2 evolution reaction. The as-obtained NiCoP@ZnCo-MOF composite displays significantly improved H2 production rates as compared to the parent MOF and their physical mixture and offers similar photocatalytic H2 evolution activity as compared to that of Pt@ZnCo-MOF. This is attributed to efficient n–n heterojunction charge separation and transfer, and rapid H2 evolution reaction dynamics by the reduction of activation energy by NiCoP cocatalyst. The H2 production rate of NiCoP@ZnCo-MOF is 8583.4 μmol h–1 g–1, 16 times higher than parent ZCM, and the apparent quantum yield (AQY) is 20.1% at 590 nm, which remained constant for a minimum of 18 h of repeated cycling in the H2 production without any degradation of the catalyst.

Ordered honeycomb-like mesoporous carbon nitride nanosheets with excess nitrogen (g-C₃N_4.5) were developed, which afford exclusive photocatalytic H₂ evolution from water.

The emerging metal-free carbon nitride (C3N4) offers prominent possibilities for realizing the highly effective hydrogen evolution reaction (HER). However, its poor surface conductivity and insufficient catalytic sites hinder the HER performance. Herein, a one-dimensional vermicular rope-like graphitic carbon nitride nanostructure is demonstrated that consists of multichannel tubular pores and high nitrogen content, which is fabricated through a cost-effective approach having the final stoichiometry g-C3N4.7 for HER application. The present g-C3N4.7 is unique owing to the presence of abundant channels for the diffusion process, modulated surface chemistry with rich-electroactive sites from N-electron lone pairs, greatly reduced recombination rate of photoexcited exciton pairs, and a high donor concentration (4.26 × 1017 cm3). The catalyst offers a visible-light-driven photocatalytic H2 evolution rate as high as 4910 μ mol h–1 g–1 with an apparent quantum yield of 14.07% at band gap absorption (2.59 eV, 479 nm) under 7.68 mW cm–2 illumination. The number of hydrogen gas molecules produced is 1.307 × 1015 s–1 cm–2, which remained constant for a minimum of 18 h of repeated cycling in the HER without any degradation of the catalyst. In density functional theory calculations, a significant change in the band offset is observed due to N doping into the system in favor of electron catalysis. The theoretical band gap of a monolayer of g-C3N4.7 was enormously reduced because of the presence of additional densities of states from the doped N atom inside the band gap. These impurity or donor bands are formed inside the band gap region, which ultimately enhance the hydrogen ion reduction reaction enormously.