Search for: All records

Identifying new catalyst composition for carbon dioxide electroreduction to high-value products has been the center of attraction over the last several years. In this article, nickel selenide (NiSe 2 ) has been identified as a high-efficiency electrocatalyst for CO 2 electroreduction at neutral pH. Interestingly, NiSe 2 shows high selectivity towards specific reduction products, forming carbon-rich C2 products like ethanol and acetic acid exclusively at lower applied potential with 98.45% faradaic efficiency, while C1 products formic acid and carbon monoxide formed preferentially at higher applied potential. More importantly, the C2 products such as acetic acid and ethanol are obtained at very low applied potential, which further corroborates the novelty of this catalyst in CO 2 utilization with minimal energy expense. The NiSe 2 catalyst surface has been studied through density functional theory calculations which show that the adsorption energy of the CO intermediate on the NiSe 2 surface is optimal for extensive reduction through formation of C–C bonds but not strong enough for surface passivation, thus leading to high selectivity for C2 products. Such high efficiency of the catalyst can be a result of increased covalency of the selenide anion along with a high d-electron density of the Ni center. The hydrothermally synthesized NiSe 2 sample also shows high activity for oxygen evolution through electrocatalytic water splitting in alkaline medium, effectively making it a bifunctional catalyst which can lower the concentration of the atmospheric pollutant CO 2 while at the same time enriching the air with O 2 . 

Transition metal selenides have attracted intensive interest as cost-effective electrocatalysts for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) because of the continuous thrust in sustainable energy conversion. In this article a Mn-based bifunctional electrocatalyst, MnSe, has been identified which shows efficient OER and ORR activity in alkaline medium. The catalytic activity could be further enhanced by using multiwalled carbon nanotubes (MWCNTs) which increases the charge transfer and electronic conductivity of the catalyst composite. This MnSe@MWCNT catalyst composite exhibits a very low overpotential of 290 mV at 10 mA cm −2 , which outperforms state-of-the-art RuO 2 as well as other oxide based electrocatalysts. Furthermore, the composite's facile OER kinetics was evidenced by its small Tafel slope of 54.76 mV dec −1 and low charge transfer resistance, indicating quick transport of the reactant species at the electrode interface. The MnSe@MWCNT also exhibited efficient electrocatalytic activity for ORR with an E onset of 0.94 V, which is among the best reported to date for chalcogenide based ORR electrocatalysts. More importantly, this MnSe-based ORR electrocatalyst exhibits high degree of methanol tolerance, showing no degradation of catalyst performance in the presence of copious quantities of methanol, thereby out-performing the state-of-the-art Pt electrocatalyst. The catalyst composite also exhibited exceptional functional and compositional stability for OER and ORR after a prolonged period of continuous operation in alkaline medium. The surface Raman analysis after OER revealed the retention of manganese selenide surface with evidence of oxo coordination, confirming the formation of an (oxy)selenide as the active surface for OER. Such efficient bifunctional OER and ORR activity makes this MnSe based catalyst attractive for overall electrolysis in regenerative as well as direct methanol fuel cells. 

CuSe nanostructures exhibit high-efficiency for glucose detection with high sensitivity (19.419 mA mM −1 cm −2 ) and selectivity at a low applied potential of +0.15 V vs. Ag|AgCl, a low detection limit of 0.196 μM and a linear range of glucose detection from 100 nM to 40 μM. 

The cobalt–seleno-based coordination complex, [Co{(SePiPr2)2N}2], is reported with respect to its catalytic activity in oxygen evolution and hydrogen evolution reactions (OER and HER, respectively) in alkaline solutions. An overpotential of 320 and 630 mV was required to achieve 10 mA cm−2 for OER and HER, respectively. The overpotential for OER of this CoSe4-containing complex is one of the lowest that has been observed until now for molecular cobalt(II) systems, under the reported conditions. In addition, this cobalt–seleno-based complex exhibits a high mass activity (14.15 A g−1) and a much higher turn-over frequency (TOF) value (0.032 s−1) at an overpotential of 300 mV. These observations confirm analogous ones already reported in the literature pertaining to the potential of molecular cobalt–seleno systems as efficient OER electrocatalysts. 

Water splitting has been widely considered to be an efficient way to generate sustainable and renewable energy resources in fuel cells, metal–air batteries and other energy conversion devices. Exploring efficient electrocatalysts to expedite the anodic oxygen evolution reaction (OER) is a crucial task that needs to be addressed in order to boost the practical application of water splitting. Intensive efforts have been devoted to develop mixed transition metal based chalcogenides as effective OER electrocatalysts. Herein, we have reported synthesis of a series of mixed metal selenides containing Co, Ni and Cu employing combinatorial electrodeposition, and systematically investigated how the transition metal doping affects the OER catalytic activity in alkaline medium. Energy dispersive spectroscopy (EDS) was performed to detect the elemental compositions and confirm the feasibility of compositional control of 66 metal selenide thin films. It was observed that the OER catalytic activity is sensitive to the concentration of Cu in the catalysts, and the catalyst activity tended to increase with increasing Cu concentration. However, increasing the Cu concentration beyond a certain limit led to decrease in catalytic efficiency, and copper selenide by itself, although catalytically active, showed higher onset potential and overpotential for OER compared to the ternary and quaternary mixed metal selenides. Interestingly, the best quaternary composition (Co 0.21 Ni 0.25 Cu 0.54 ) 3 Se 2 showed similar crystal structure as its parent compound of Cu 3 Se 2 with slight decrease in lattice spacings of (101) and (210) lattice planes (0.0222 Å and 0.0148 Å, respectively) evident from the powder X-ray diffraction pattern. (Co 0.21 Ni 0.25 Cu 0.54 ) 3 Se 2 thin film exhibited excellent OER catalytic activity and required an overpotential of 272 mV to reach a current density of 10 mA cm −2 , which is 54 mV lower than Cu 3 Se 2 , indicating a synergistic effect of transition metal doping in enhancing catalytic activity. 

Uniform and porous CoNi 2 Se 4 was successfully synthesized by electrodeposition onto a composite electrode comprising reduced graphene oxide (rGO) anchored on a Ni foam substrate (prepared hydrothermally). This CoNi 2 Se 4 –rGO@NF composite electrode has been employed as an electrocatalyst for the direct oxidation of glucose, thereby acting as a high-performance non-enzymatic glucose sensor. Direct electrochemical measurement with the as-prepared electrode in 0.1 M NaOH revealed that the CoNi 2 Se 4 –rGO nanocomposite has excellent electrocatalytic activity towards glucose oxidation in an alkaline medium with a sensitivity of 18.89 mA mM −1 cm −2 and a wide linear response from 1 μM to 4.0 mM at a low applied potential of +0.35 V vs. Ag|AgCl. This study also highlights the effect of decreasing the anion electronegativity on enhancing the electrocatalytic efficiency by lowering the potential needed for glucose oxidation. The catalyst composite also exhibits high selectivity towards glucose oxidation in the presence of several interferents normally found in physiological blood samples. A low glucose detection limit of 0.65 μM and long-term stability along with a short response time of approximately 4 seconds highlights the promising performance of the CoNi 2 Se 4 –rGO@NF electrode for non-enzymatic glucose sensing with high precision and reliability.