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Energy harvesting from solar and water has created ripples in materials energy research for the last several decades, complemented by the rise of Hydrogen as a clean fuel. Among these, water electrolysis leading to generation of oxygen and hydrogen, has been one of the most promising routes towards sustainable alternative energy generation and storage, with applications ranging from metal-air batteries, fuel cells, to solar-to-fuel energy conversion systems. In fact, solar water splitting is one of the most promising method to produce Hydrogen without depleting fossil-fuel based natural resources. However, the efficiency and practical feasibility of water electrolysis is limited by the anodic oxygen evolution reaction (OER), which is a kinetically sluggish, electron-intensive uphill reaction. A slow OER process also slows the other half- cell reaction, i.e. the hydrogen evolution reaction (HER) at the cathode. Hence, designing efficient catalysts for OER process from earth-abundant resources has been one of the primary concerns for advancing solar water splitting. In the Nath group we have focused on transition metal chalcogenides as efficient OER electrocatalysts. We have proposed the idea that these chalcogenides, specifically, selenides and tellurides will show much better OER catalytic activity due to increasing covalency around the catalytically active transition metal site, compared to the oxides caused by decreasing electronegativity of the anion, which in turn leads to variation of chem. potential around the transition metal center, [e.g. lowering the Ni 2+ --> Ni 3+ oxidn. potential in Ni-based catalysts where Ni 3+ is the actually catalytically active species]. Based on such hypothesis, we have synthesized a plethora of transition metal selenides including those based on Ni, Ni-Fe, Co, and Ni-Co, which show high catalytic efficiency characterized by low onset potential and overpotential at 10 mA/cm 2 [Ni 3 Se 2 - 200 - 290 mV; Co 7 Se 8 - 260 mV; FeNi 2 Se 4 -NrGO - 170 mV (NrGO - N-doped reduced graphene oxide); NiFe 2 Se 4 - 210 mV; CoNi 2 Se 4 - 190 mV; Ni 3 Te 2 - 180 mV].
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Molecular Cluster Complex of High-Valence Chromium Selenide Carbonyl as Effective Electrocatalyst for Water Oxidation
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.
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- PAR ID:
- 10423778
- Publisher / Repository:
- MDPI
- Date Published:
- Journal Name:
- Catalysts
- Volume:
- 13
- Issue:
- 4
- ISSN:
- 2073-4344
- Page Range / eLocation ID:
- 721
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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The advancement of affordable, high-efficiency electrocatalysts for the oxygen evolution reaction (OER) is essential for addressing kinetic limitations in electrochemical water-splitting technologies. Transition metal chalcogenides have surfaced as compelling options owing to their favorable electrochemical tunability, enhanced lattice conductivity, abundance in nature, and economic viability. Manganese-based selenides stand out because of the inherent multivalent redox transitions of Mn (Mn²⁺/Mn³⁺/Mn⁴⁺), which enable intricate multi-electron transfer processes crucial for OER. The addition of selenium enhances lattice covalency which in turn improves intrinsic electrical conductivity and modifies the local electronic environment, leading to enhanced charge transfer kinetics and better intermediate adsorption. Mn selenides experience surface reconstruction during OER conditions, resulting in the formation of catalytically active mixed anionic oxyselenide phases which further enhances catalyst activation through anchoring hydroxyl group on the catalytically transition metal site. Additionally, Jahn–Teller distortions linked to Mn³⁺ can also influence the electrochemical water oxidation by enhancing intermediate adsorption through alterations in the local coordination geometry. In addition to the inherent electronic and redox characteristics, external factors like morphology also play a crucial role in influencing catalytic performance. In this presentation, we will discuss the investigation of manganese selenide (MnSe₂) nanostructures as electrocatalysts for water oxidation and highlight the influence of morphology on the electrocatalytic activity. The MnSe2nanostructures with precise morphologies such as spheres and cubes were synthesized by hydrothermal methods where subtle variation in the reaction conditions led to different morphologies. These different morphologies demonstrate unique surface areas, active site exposure, and mass transport properties. Spherical morphologies offer elevated surface-to-volume ratios and isotropic facet exposure, which improves the electrolyte accessibility and fosters consistent catalytic activity. Cubic morphologies, on the other hand, tend to reveal crystallographic planes that can significantly boost the adsorption and transformation of OER intermediates, thereby enhancing catalytic turnover efficiency. MnSe₂ structures exhibiting a variety of morphologies, spherical and cubic, were synthesized using a straightforward one-step hydrothermal method. The compositional and phase purity of the as-prepared sample was validated through structural and surface analyses such as powder X-ray diffraction (PXRD), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS).Scanning electron microscopy (SEM) highlighted the various morphologies of MnSe₂ obtained under different reaction conditions. While bulk MnSe2showed superior OER activity exhibiting a low overpotential of 200 mV at10 mA/cm2, nanostructuring the catalyst improved the electrocatalytic performance. Spherical MnSe₂ demonstrated exceptional OER activity, reaching a low overpotential of 190 mV at a current density of 10 mA cm⁻² and a Tafel slope of 98 mV dec⁻¹ in 1.0 M KOH. The MnSe2electrocatalyst also exhibited remarkable electrochemical stability, sustaining steady activity for 24 hours of uninterrupted operation at 1.45 V vs. RHE This study highlights the not-so-explored power of Mn as the catalytic center for electrochemical water oxidation. It also underscores the essential influence of morphological control on charge transport, surface reactivity, and catalytic efficiency in manganese-based selenides. The results demonstrate that MnSe₂ serves as a highly efficient, readily available electrocatalyst for the oxygen evolution reaction, highlighting the significance of morphology-focused design approaches in the progression of water-splitting technologies and renewable energy solutions. Figure 1more » « less
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