Ni3Te2 has been reported as a highly efficient OER electrocatalyst with an overpotential of 180 mV at 10 mA cm−2 and also showing HER catalytic activity in alkaline medium.

Electrodeposited Co7Se8 nanostructures exhibiting flake-like morphology show bifunctional catalytic activity for oxygen evolution and hydrogen evolution reaction (OER and HER, respectively) in alkaline medium with long-term durability (>12 h) and high Faradaic efficiency (99.62%). In addition to low Tafel slope (32.6 mV per decade), the Co7Se8 OER electrocatalyst also exhibited very low overpotential to achieve 10 mA cm(-2) (0.26 V) which is lower than other transition metal chalcogenide based OER electrocatalysts reported in the literature and significantly lower than the state-of-the-art precious metal oxides. A low Tafel slope (59.1 mV per decade) was also obtained for the HER catalytic activity in alkaline electrolyte. The OER catalytic activity could be further improved by creating arrays of 3-dimensional rod-like and tubular structures of Co7Se8 through confined electrodeposition on lithographically patterned nanoelectrodes. Such arrays of patterned nanostructures produced exceptionally high mass activity and gravimetric current density (∼68 000 A g(-1)) compared to the planar thin films (∼220 A g(-1)). Such high mass activity of the catalysts underlines reduction in usage of the active material without compromising efficiency and their practical applicability. The catalyst layer could be electrodeposited on different substrates, and an effect of the substrate surface on the catalytic activity was also investigated. The Co7Se8 bifunctional catalyst enabled water electrolysis in alkaline solution at a cell voltage of 1.6 V. The electrodeposition works with exceptional reproducibility on any conducting substrate and shows unprecedented catalytic performance especially with the patterned growth of catalyst rods and tubes.

Designing high-efficiency water oxidation catalysts from earth-abundant resources has attracted significant attention in the last couple of years owing to the potential application of this technology in several energy conversion devices. Among the transition metals, copper is one of the cheapest earth-abundant nonprecious element which can enhance electrocatalytic activity due to heavily occupied d-orbitals. In this article we have shown electrocatalytic activity of copper selenide for the first time for water oxidation reaction. The copper selenide phases were synthesized by direct electrodeposition on electrodes, as well as by hydrothermal and chemical vapor deposition (CVD) techniques. Structure and morphology characterization through powder X-ray diffraction, Raman, X-photoelectron spectroscopy, and electron microscopy revealed that all the synthesized phases were pure crystalline copper selenide of composition Cu 2 Se and comprising nanostructured granular morphology. Electrocatalytic performance for water oxidation was investigated in alkaline solution (1 M KOH) and it was observed that Cu 2 Se showed a low overpotential of only 270 mV to achieve 10 mA cm −2 . This catalyst also displayed a low Tafel slope of 48.1 mV dec −1 . Interestingly Cu 2 Se showed comparable electrocatalytic activity irrespective of the method of synthesis indicating that it is indeed an intrinsic property of the material. Chronoamperometric studies revealed that the catalyst retained its activity for prolonged periods of continuous oxygen evolution exceeded 6 h, while postactivity characterization revealed that crystallinity and surface composition was preserved after catalytic activity. Because copper selenides can be found in nature as stable minerals, this article can initiate a new concept for efficient catalyst design.

Herein we have shown that electrodeposited NiSe2 can be used as a bifunctional electrocatalyst under alkaline conditions to split water at very low potential by catalyzing both oxygen evolution and hydrogen evolution reactions at anode and cathode, respectively, achieving a very high electrolysis energy efficiency exceeding 80% at considerably high current densities (100 mA cm−2). The OER catalytic activity as well as electrolysis energy efficiency surpasses any previously reported OER electrocatalyst in alkaline medium and energy efficiency of an electrolyzer using state-of-the-art Pt and RuO2 as the HER and OER catalyst, respectively. Through detailed electrochemical and structural characterization, we have shown that the enhanced catalytic activity is attributed to directional growth of the electrodeposited film that exposes a Ni-rich lattice plane as the terminating plane, as well as increased covalency of the selenide lattice which decreases the Ni(II) to Ni(III) oxidation potential. Thereby, the high efficiency along with extended stability makes NiSe2 as the most efficient water electrolyzer known to-date.

Cobalt telluride has been identified as an efficient multifunctional electrocatalyst for oxygen and hydrogen evolution reactions and oxygen reduction reaction in alkaline medium. Both hydrothermally synthesized and electrodeposited, CoTe and CoTe2 show efficient electrocatalytic activities. CoTe shows better efficiency for OER with a low Tafel slope (43.8 mV dec–1) and lower overpotential (200 mV) at 10 mA cm–2 compared to CoTe2. DFT studies have also been performed which revealed that CoTe showed higher adsorption energy for intermediate −OH adsorption on the catalyst surface, which corresponds to the catalyst activation step. Comparison of the −OH adsorption energies (E ads) on different catalyst surfaces with the observed overpotential also revealed that this E ads can be used as an appropriate descriptor for benchmarking catalytic efficiencies. Both CoTe and CoTe2 exhibited improved OER catalytic efficiency compared to Co3O4, confirming the primary hypothesis that decreasing anion electronegativity enhances catalytic efficiency by virtue of increasing lattice covalency around the catalytically active site. The difference in OER catalytic activity between CoTe and CoTe2 could be explained from fundamental materials chemistry concepts by comparing their lattice structures which showed different packing density of catalytically active Co sites as well as varying unsaturation of Co-terminated surfaces. Band structure calculations also corroborated such differences and could potentially explain the difference in activity due to observed differences in electron density distribution around the catalytically active Co site. The cobalt telluride compositions also showed moderate HER and ORR activity in alkaline medium, making them trifunctional catalysts which can be used in practical devices. Both CoTe and CoTe2 showed extensive functional and compositional stability for OER, HER, and ORR, under continuous operation in alkaline medium for over 24 h with less than 5% degradation of current density. The excellent compositional stability of each catalyst was revealed by detailed electrochemical measurements and surface and bulk analytical characterizations, which confirmed that there was no catalyst leaching even with long-term operation and no other impurity enrichment in the electrolyte.