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.

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.

Underlying factors responsible for superior phase-dependent electrocatalytic OER activity of crystalline Co-vanadates are investigated. Previous reports on Co-vanadates ascribed activity differences to optimal metal–oxygen bond strength. In contrast, we found etching of vanadate from precatalyst during electrochemical activation to be the primary contributor. The resulting higher surface reconstruction exposes a higher number of catalytically active cobalt sites that otherwise lay inactive due to their position in bulk. Co-vanadates with polymeric vanadates (CoV2O6) showed better OER over monomeric orthovanadates (Co3V2O8) due to higher vanadate etching. Further, this work validates that etching can happen even from lattice positions, where bonding between constituents is strong.

The quest toward finding an efficient oxygen evolution reaction (OER) catalyst utilizing a sustainable and facile synthetic strategy is still underway. Low overpotential, better stability, and rapid kinetics are the key features to be considered while designing a competent OER catalyst. Herein, we have developed a rapid and efficient wet chemical route for the synthesis of a cobalt-and silver-based precatalytic oxalate (CoC 2 O 4 /Ag 2 C 2 O 4 ) framework via a rapid precipitation method at room temperature. The optimized catalyst required an overpotential of 260 mV to reach the benchmark current density of 10 mA/cm 2 geo , with a Tafel slope value of 47 mV/dec. It has also shown 72 h of chronopotentiometry stability as well as 1000 cycles of potentiodynamic stability along with 90% Faradaic efficiency in 1(M) KOH for OER. Addition of a minimal amount of silver component assists in the reduction of overpotential up to 120 mV compared to CoC 2 O 4 . Furthermore, the minimal amount of silver inclusion improved the charge migration property via lowering the charge-transfer resistance besides tuning the charge storage mechanism (b value). The paradigm shift in catalytic efficiency can be manifested by calculating both intrinsic (persite activity) and geometric (based on the effective area of electrode materials) activities. Interestingly, significant improvement in C dl (double-layer capacitance) from 10.25 to 19.59 mF/cm 2 is achieved upon silver component inclusion, indicating a higher number of accessible catalytic sites for alkaline OER. The turnover frequency value further authenticates the importance of silver component in the precatalytic oxalate network for intrinsic catalytic activity under alkaline conditions. The mechanistic trajectory is also investigated from the proton reaction order (ρRHE), revealing the occurrence of the proton-decoupled electron transfer process for the optimized catalyst. The results reveal the efficient electrochemical surface reconstruction in the cobalt-and silver-based precatalytic oxalate framework for improved alkaline water oxidation through exposing the surface as well as bulk active centers for easy electrolyte diffusion in alkaline medium.

The electrocatalytic performance of transition metal dichalcogenides (TMDs) can be hugely impacted by their phase and electronic structure. In this regard, stabilization of the 1T (metallic) phase is a substantial challenge to attain superior electrocatalytic activity compared to its thermodynamically stable polymorph (2H phase). This report provides a simple approach to introduce the 1T phase into 2H−MoSe2 through heteroatom (Cr3+) doping using a hydrothermal method. 1T/2H−MoSe2 (x Cr) (x=1,2,3 and 5) materials have shown better electrocatalytic HER activities compared to the 2H−MoSe2, especially 2% Cr3+ doped MoSe2 (1T/2H−MoSe2 (2 Cr)) have shown the best catalytic activity. 1T/2H−MoSe2 (2 Cr) exhibits a current density of 20 mA cm−2 at an overpotential of 176 mV, low Tafel slope of 77 mV/dec, high double layer capacitance (Cdl) of 78.3 mF cm−2 and good cyclic stability. The improved electrocatalytic activity of 1T/2H−MoSe2 (2 Cr) could be attributed to the high conductance, high 1T phase content and the greater number of active sites resulting from the introduction of Cr3+ ions into MoSe2. In addition, density functional theory (DFT) studies predict that the introduction of Cr3+ ions into the MoSe2 monolayer increases the conduction electron density in the basal plane at room temperature which in turn supports the generation of additional active sites along the basal plane.