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Designing highly active and robust catalysts for the oxygen evolution reaction is key to improving the overall efficiency of the water splitting reaction. It has been previously demonstrated that evaporation induced self‐assembly (EISA) can be used to synthesize highly porous and high surface area cerate‐based fluorite nanocatalysts, and that substitution of Ce with 50% rare earth (RE) cations significantly improves electrocatalyst activity. Herein, the defect structure of the best performing nanocatalyst in the series are further explored, Nd₂Ce₂O₇, with a combination of neutron diffraction and neutron pair distribution function analysis. It is found that Nd^{3 +}cation substitution for Ce in the CeO₂fluorite lattice introduces higher levels of oxygen Frenkel defects and induces a partially reduced RE_1.5Ce_1.5O_{5 +x}phase with oxygen vacancy ordering. Significantly, it is demonstrated that the concentration of oxygen Frenkel defects and improved electrocatalytic activity can be further enhanced by increasing the compositional complexity (number of RE cations involved) in the substitution. The resulting novel compositionally‐complex fluorite– (La_0.2Pr_0.2Nd_0.2Tb_0.2Dy_0.2)₂Ce₂O₇is shown to display a low OER overpotential of 210 mV at a current density of 10 mAcm⁻²in 1M KOH, and excellent cycling stability. It is suggested that increasing the compositional complexity of fluorite nanocatalysts expands the ability to tailor catalyst design.

 

Anion-tuning in metallic chalcogenides has been shown to have a significant impact on their electrocatalytic ability for overall water splitting. In this article, copper-based chalcogenides (Cu₂X, X= O, S, Se, and Te) have been systematically studied to examine the effect of decreasing anion electronegativity and increasing covalency on the electrocatalytic performance. Among the copper chalcogenides, Cu₂Te has the highest oxygen evolution reaction (OER) activity and can sustain high current density of 10 and 50 mA cm⁻²for 12 h. The difference in intrinsic catalytic activity of these chalcogenide surfaces have been also probed through density functional theory calculations, which was used to estimate energy of the catalyst activation step. It was observed that the hydroxyl adsorption on the surface catalytic site is critically important for the onset and progress of OER activity. Consequently, it was also observed that the –OH adsorption energy can be used as a simple but accurate descriptor to explain the catalytic efficiency through volcano-like correlation plot. Such observation will have a significant impact on developing design principle for optimal catalytic surface exhibiting high performance as well as prolonged stability.

 

Developing simple, affordable, and environmentally friendly water oxidation electrocatalysts with high intrinsic activity and low overpotential continues to be an area of intense research. In this article, a trichromium diselenide carbonyl cluster complex (Et4N)2[Se2Cr3(CO)10], with a unique bonding structure comprising bridging Se groups, has been identified as a promising electrocatalyst for oxygen evolution reaction (OER). This carbonyl cluster exhibits a promising overpotential of 310 mV and a low Tafel slope of 82.0 mV dec−1 at 10 mAcm−2, with superior durability in an alkaline medium, for a prolonged period of continuous oxygen evolution. The mass activity and turnover frequency of 62.2 Ag−1 and 0.0174 s−1 was achieved, respectively at 0.390 V vs. RHE. The Cr-complex reported here shows distinctly different catalytic activity based on subtle changes in the ligand chemistry around the catalytically active Cr site. Such dependence further corroborates the critical influence of ligand coordination on the electron density distribution which further affects the electrochemical activation and catalytic efficiency of the active site. Specifically, even partial substitution with more electronegative substituents leads to the weakening of the catalytic efficiency. This report further demonstrates that metal carbonyl chalcogenides cluster-type materials which exhibit partially occupied sites and high valence in their metal sites can serve as catalytically active centers to catalyze OER exhibiting high intrinsic activity. The insight generated from this report can be directly extrapolated to 3-dimensional solids containing similar structural motifs, thereby aiding in optimal catalyst design. 

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 . 

Recent emphasis on carbon dioxide utilization has necessitated the exploration of different catalyst compositions other than copper-based systems that can significantly improve the activity and selectivity towards specific CO₂ reduction products at low applied potential. In this study, a binary CoTe has been reported as an efficient electrocatalyst for CO₂reduction in aqueous medium under ambient conditions at neutral pH. CoTe showed high Faradaic efficiency and selectivity of 86.83 and 75%, respectively, for acetic acid at very low potential of − 0.25 V vs RHE. More intriguingly, C1 products like formic acid was formed preferentially at slightly higher applied potential achieving high formation rate of 547.24 μmol cm⁻² h⁻¹ at − 1.1 V vs RHE. CoTe showed better CO2RR activity when compared with Co₃O₄, which can be attributed to the enhanced electrochemical activity of the catalytically active transition metal center as well as improved intermediate adsorption on the catalyst surface. While reduced anion electronegativity and improved lattice covalency in tellurides enhance the electrochemical activity of Co, high d-electron density improves the intermediate CO adsorption on the catalyst site leading to CO₂reduction at lower applied potential and high selectivity for C₂products. CoTe also shows stable CO2RR catalytic activity for 50 h and low Tafel slope (50.3 mV dec^–1) indicating faster reaction kinetics and robust functionality. Selective formation of value-added C₂products with low energy expense can make these catalysts potentially viable for integration with other CO₂capture technologies thereby, helping to close the carbon loop.

 

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. 

Developing protocols for designing high‐efficiency, durable, cost‐effective electrocatalysts for oxygen evolution reaction (OER) necessitates deeper understanding of structure–property correlation as a function of composition. Herein, it has been demonstrated that incorporating tellurium into binary nickel chalcogenide (NiSe) and creating a mixed anionic phase perturbs its electronic structure and significantly enhances the OER activity. A series of nanostructured nickel chalcogenides comprising a layer‐by‐layer morphology along with mixed anionic ternary phase are grown in situ on nickel foam with varying morphological textures using simple hydrothermal synthesis route. Comprehensive X‐ray diffraction, X‐ray photoelectron spectroscopy, and in situ Raman spectroscopy analysis confirms the formation of a trigonal single‐phase nanocrystalline nickel (telluro)‐selenide (NiSeTe) as a truly mixed anionic composition. The NiSeTe electrocatalyst exhibits excellent OER performance, with a low overpotential of 300 mV at 50 mA cm⁻²and a small Tafel slope of 98 mV dec⁻¹in 1 mKOH electrolyte. The turnover frequency and mass activity are 0.047 s⁻¹and 90.3 Ag⁻¹, respectively. Detailed electrochemical measurements also reveal enhanced charge transfer properties of the NiSeTe phase compared to the mixture of binaries. Density functional theory calculations reveal favorable OH adsorption energy in the mixed anionic phase compared to the binary chalcogenides confirming superior electrocatalytic property.