layered materials are currently one of the most explored materials for developing efficient and stable electrocatalysts in energy conversion applications. Some of the 2D metal phosphorous trichalcogenides (M 2 P 2 X 6 or MPX 3 in its simplified form) have been reported to be useful catalysts for water splitting, although results have been less promising for the sluggish oxygen evolution reaction (OER) due to insufficient activity or compromised stability. Herein, we report the OER catalysis of a series of M 2 P 2 X 6 (M 2+ = Mn, Fe, Co, Zn, Cd; X = S, Se). From the series of MPX 3 , CoPS 3 yields the best results with an overpotential within the range of values usually obtained for IrO 2 or RuO 2 catalysts. The liquid-phase exfoliation of CoPS 3 even improves the OER activity due to abundant active edges of the downsized sheets, accompanied by the presence of surface oxides. The influence of the OER medium and underlying substrate electrode is studied, with the exfoliated CoPS 3 reaching the lowest overpotential at 234 mV at a current density of 10 mA/cm 2 , also able to sustain high current densities, with an overpotential of 388 mV at a current density of 100 mA/cm 2 , and excellent stability after multiple cycles or long-term operation. Quantum chemical models reveal that these observations are likely tied to moieties on CoPS 3 edges, which are responsible for low overpotentials through a two-site mechanism. The OER performance of exfoliated CoPS 3 reported herein yields competitive values compared to those reported for other Co-based and MPX 3 in the literature, thus holding substantial promise for use as an efficient material for the anodic water-splitting reaction.
Promising applications of metal phosphorous trichalcogenides (M2P2X6 or MPX3) have been predicted in optoelectronics, photoelectrocatalysis, and water‐splitting reactions, mainly due to its wide bandgap. Transition metals are widely used in the synthesis of MPX3, however, divalent cations of alkaline earth metals can also be constituents in MPX3 2D layered structures. Herein, MgPX3 (X = S, Se) are synthesized and their photoelectrochemical (PEC) activity is tested in the hydrogen evolution and oxygen evolution reaction (OER) regions under a wide range of wavelengths. MgPSe3 photoelectrode shows the best PEC performance with a response of 1.6 ± 0.1 mA cm−2 under 420 nm. In the light‐assisted OER, a 200 mV improvement is obtained in the overpotential at 10 mA cm−2 for MgPSe3. The better performance of MgPSe3 is consistent with its lower optical bandgap (Eg = 3.15 eV), as a result of the variation of electronegativity between selenide and sulfide.
conversion and storage systems in which electrocatalytic water splitting reactions are included. [1] Hydrogen production from water electrolysis is considered a sustainable alternative since its by-product is water, but the biggest challenge in the development of electrocatalysts remains in overcoming the reaction kinetics of hydrogen evolution reaction (HER), especially in alkaline electrolytes due to additional water dissociation step which requires high overpotentials to initiate the catalysis. [2][3][4] Noble metals such as platinum, ruthenium, or iridium are conventional and satisfactory catalysts for water splitting reactions, however, their scarcity and high cost are limitations in large-scale production which has conducted intensive research to find more accessible materials to replace such precious metals. In the vast diversity of investigated materials, 2D materials have been reported as candidates for HER due to their tunable and uniformly exposed lattice planes and unique electronic state, [5,6] and among them, metal phosphorous trichalcogenides (MPX 3 ) have emerged as promising electrocatalysts. [7][8][9] Their general chemical formula is M II 2 [P 2 X 6 ] 4− , with the additional mixed metal configurations of M I 2 M II [P 2 X 6 ] 4− , and M I M III [P 2 X 6 ] 4− being possible, where X = S, Se, and in which metal cations stabilize a thiophosphate [P 2 S 6 ] 4− or selenophosphate [P 2 Se 6 ] 4− anionic framework forming layers that are weakly bonded together through van der Waals interactions. [8] Great progress has been achieved with M II 2 [P 2 X 6 ] 4− , or MPX 3 in its simplified formula, as HER electrocatalysts in alkaline media with reports on FePS 3 , [10] NiPS 3 , [11] and MnPX 3 . [12] Still in the HER region, the MPX 3 have also revealed significant enhancement for photocatalytic water splitting but the research trends remain on Fe-, [13,14] Mn-, [14,15] Cd-, [14] and ZnPX 3 [14] materials. Reports on Ni- [14] or MgPX 3 [16] materials are also found. So, all these works opened a new avenue for MPX 3 electrocatalysts thus raising interest in replacing the divalent metal with univalent and trivalent metals to investigate the catalytic performance of layered M I M III P 2 X 6 structures. A stable photoelectrochemical HER has been reported for CuInP 2 S 6 [17,18] and Ag 0.5 In 0.5 P 2 X 6 [14] compounds; however, HER in alkaline mediaConsiderable improvements in the electrocatalytic activity of 2D metal phosphorous trichalcogenides (M 2 P 2 X 6 ) have been achieved for water electrolysis, mostly with M II 2 [P 2 X 6 ] 4− as catalysts for hydrogen evolution reaction (HER). Herein, M I M III P 2 S 6 (M I = Cu, Ag; M III = Sc, V, Cr, In) are synthesized and tested for the first time as electrocatalysts in alkaline media, towards oxygen reduction reaction (ORR) and HER. AgScP 2 S 6 follows a 4 e − pathway for the ORR at 0.74 V versus reversible hydrogen electrode; CuScP 2 S 6 is active for HER, exhibiting an overpotential of 407 mV and a Tafel slope of 90 mV dec −1 . Density functional theory mod...
Abstract2D layered materials are currently one of the most explored materials in developing efficient and stable photoelectrocatalysts in energy conversion applications. Some of the 2D metal phosphorus chalcogenides (M2P2X6 or plainly MPX3) have been reported to be useful catalysts for water splitting. Herein, the photoresponsivity of a series of synthesized M2P2X6 (M2+ = Mn, Fe, Co, Zn, Cd; X = S, Se), tested for the oxygen evolution reaction (OER) region in alkaline media, with excitation wavelengths from 385 to 700 nm, is reported. The experimentally determined optical bandgaps of the MPX3 materials range from 1.5 eV for FePSe3 to 3.7 eV for ZnPS3. At +1.23 V versus reversible hydrogen electrode (RHE), the photoelectrochemical (PEC) activity in the OER region of MnPSe3 exhibits superior performance, while the exfoliation of CoPS3 improves its PEC activity up to double in contrast with its bulk counterpart. The influence of the substrate (glassy carbon (GC), indium tin oxide (ITO), and aluminum‐doped zinc oxide (AZO)) and applied potential is also studied. Exfoliated CoPS3 reaches a photoresponsivity of up to 0.6 mA W‐1 under 450 nm excitation wavelength and at +1.23 V versus RHE in alkaline electrolyte.
The development of sensitive, selective, and reliable gaseous hydrogen peroxide (H2O2) sensors operating at room temperature still represents a remaining challenge. In this work, we have investigated and combined the advantageous properties of a two-dimensional Ti3C2T x MXene material that exhibits a large specific surface area and high surface activity, with favorable conducting and stabilizing properties of chitosan. The MXene–chitosan membrane was deposited on the ferrocyanide-modified screen-printed working carbon electrode, followed by applying poly(acrylic acid) as an electrolyte and accumulation medium for gaseous H2O2. The sensor showed highly sensitive and selective electroanalytical performance for detecting trace concentrations of gaseous H2O2 with a very low detection limit of 4 μg m–3 (4 ppbv), linear response in the studied concentration range of 0.5–30.0 mg m–3, and good reproducibility with an RSD of 1.3%. The applicability of the sensor was demonstrated by point-of-interest detection of gaseous H2O2 during the real hair bleaching process with a 9 and 12% H2O2 solution.
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