Catalyzing hydrogen evolution reaction in alkali media is challenging owing to the sluggish kinetics, originated from the water dissociation process. In this context, synergistic coupling between Ni/Co-based materials with transition metal dichalcogenides (TMDs) often accelerates the alkaline hydrogen evolution reaction (HER). Significant interaction between the two components and active-site density are the keys for achieving a promising catalytic activity. This report emphasizes a two-step selenization approach to prepare a Ni0.85Se/MoSe2 interfacial structure with abundant active sites. Initially, Ni0.75Se nanoparticles were prepared using the solvothermal method and subsequently employed them as a support for the growth of MoSe2 under hydrothermal conditions. This resulted in the formation of a Ni0.85Se/MoSe2 interfacial structure. The results of physical characterization techniques confirm the significant interaction between Ni0.85Se and MoSe2. The interfacial structures showed a superior HER activity in alkali media compared to the individual components; especially, Ni0.85Se/MoSe2 (20) delivers a current density of 10 mA cm–2 at an overpotential of 108 mV. The improved HER activity of the interfacial structure is attributed to the (i) efficient water dissociation process over the Ni0.85Se promoter and (ii) exposure of more catalytic active sites (edges) of MoSe2. In addition, as-prepared Ni0.75Se exhibits a better oxygen evolution reaction (OER) activity by delivering a current density of 10 mA cm–2 at an overpotential of 340 mV. Furthermore, overall water splitting has been demonstrated by constructing an electrolyzer using Ni0.85Se/MoSe2 (20) and Ni0.75Se as a cathode and anode, respectively. The electrolyzer delivers a current density of 10 mA cm–2 at a cell potential of 1.7 V. The long-term stability experiment and the post catalytic characterization reveals the high robustness of the Ni0.85Se/MoSe2 interfacial structure.

The development of MoS2 in the metallic phase (1T‐MoS2) is of paramount interest as it exhibits superior electrochemical activities compared to its semiconducting polymorph (2H‐MoS2). In this work, an ionic liquid (IL)‐assisted solvothermal method was employed to produce the thermodynamically metastable 1T‐MoS2. Structural characterization of the material suggests the intercalation of the IL into MoS2. De‐intercalation of ILs from 1T‐MoS2 leads to the formation of 2H‐MoS2. Carbon cloth‐supported 1T‐MoS2(1T‐MoS2@CC) shows higher electrocatalytic activity towards acidic hydrogen evolution reaction (HER) by delivering a current density of 50 mA/cm2 at an overpotential of 210 mV whereas 2H‐MoS2@CC requires an overpotential of 260 mV to reach the same current density. In addition, the 1T‐MoS2@CC electrode delivers a high electrochemical double‐layer storage ability compared to 2H‐MoS2@CC in 1 M Na2SO4. The enhanced electrochemical activity of 1T‐MoS2 over 2H‐MoS2 may be due to the existence of conducting basal planes and the high interlayer spacing (about 1 nm) caused by the intercalation of ILs into the MoS2 layers.

Developing electrocatalysts with abundant active sites is a substantial challenge to reduce the overpotential requirement for the alkaline oxygen evolution reaction (OER). In this work, we have aimed to improve the catalytic activity of cobalt selenides by growing them over the self-supported Co3O4 microrods. Initially, Co3O4 microrods were synthesized through annealing of an as-prepared cobalt oxalate precursor. The subsequent selenization of Co3O4 resulted in the formation of a grainy rodlike Co3O4/Co0.85Se/Co9Se8 network. The structural and morphological analysis reveals the presence of Co3O4 even after the selenization treatment where the cobalt selenide nanograins are randomly covered over the Co3O4 support. The resultant electrode shows superior electrocatalytic activity toward OER in alkaline medium by delivering a benchmark current density of 10 mA/cm2 geo at an overpotential of 330 mV. As a comparison, we have developed Co0.85Se/Co9Se8 under similar conditions and evaluated its OER activity. This material consumes an overpotential of 360 mV to deliver the benchmark current density, which signifies the role of the Co3O4 support to improve the electrocatalytic activity of Co0.85Se/Co9Se8. Despite having a low TOF value for Co3O4/Co0.85Se/Co9Se8 (0.0076 s–1) compared to Co0.85Se/Co9Se8 (0.0102 s–1), the improved catalytic activity of Co3O4/Co0.85Se/Co9Se8 is attributed to the presence of a higher number of active sites rather than the improved per site activity. This is further supported from the C dl (double layer capacitance) measurements where Co3O4/Co0.85Se/Co9Se8 and Co0.85Se/Co9Se8 tender C dl values of about 8.19 and 1.08 mF/cm2, respectively, after electrochemical precondition. As-prepared Co3O4/Co0.85Se/Co9Se8 also manifests rapid kinetics (low Tafel slope ∼ 91 mV/dec), long-term stability, low charge-transfer resistance, and 82% Faradaic efficiency for alkaline electrocatalysis (pH = 14). Furthermore, the proton reaction order (ρRHE) is found to be 0.65, indicating a proton decoupled electron transfer (PDET) mechanism for alkaline OER. Thus, the Co3O4 support helps in the exposure of more catalytic sites of Co0.85Se/Co9Se8 to deliver the improved catalytic activities in alkaline medium.

The electrocatalytic oxygen evolution reaction (OER) demands an efficient catalyst with low overpotential, rapid kinetics, and long-term stability. Herein, we demonstrate the activity of molybdenum oxide (MoO 2 )-embedded cobalt oxalate (CoC 2 O 4 • 2H 2 O) nanostructures for the OER process. The excellent performance of the microrod-like MoO 2 /CoC 2 O 4 •2H 2 O composite is reflected in just 330 mV overpotential for 10 mA/cm geo 2 , low Tafel slope (78 mV/dec), 90% faradaic efficiency, and 24 h stability in 1.0 (M) KOH. The as-prepared electrocatalyst requires a significantly lower overpotential wrt CoC 2 O 4 •2H 2 O. Incorporation of MoO 2 elegantly modified the textural property, such as surface area and porosity, of the as-prepared material. Furthermore, MoO 2 / CoC 2 O 4 •2H 2 O was found to follow the proton-decoupled electrontransfer mechanism for electrocatalyzing OER. Postcatalytic characterization revealed the electrochemical transformation of a one-dimensional (1-D) MoO 2 /CoC 2 O 4 •2H 2 O microrod into a sheetlike two-dimensional α-Co(OH) 2 /CoOOH during alkaline OER. Interestingly, postcatalytic X-ray photoelectron spectroscopy, inductively coupled plasma, and energy-dispersive X-ray spectroscopy analyses suggest MoO 2 etching from the material, leading to exposure of a higher number of electrochemically active sites that otherwise lay inactive because of their presence in the bulk. Both CoC 2 O 4 •2H 2 O-and MoO 2 /CoC 2 O 4 •2H 2 O-integrated 1-D nanostructures showed an ∼0.01 s −1 turnover frequency value at 400 mV overpotential.We believe that the enhancement in geometrical electrocatalytic activity is not due to the direct participation of MoO 2 in catalysis but due to its electrochemical etching, which makes a higher number of catalytically active sites accessible to the electrolyte. This study conveys the in situ electrochemical activation strategy through etching of pore additive for the alkaline OER process.

Nickel–cobalt oxalate (Ni2.5Co5C2O4–nH2O) based block-like nanostructure has been introduced as superior electrocatalyst compared to nickel–cobalt oxide (NiCo2O4) for alkaline water oxidation.