Manjeet Chhetri
Postdoctoral Fellow, Electrochemistry
Selected Project works
What can we do with bipolar membranes?
Bipolar membranes (BPMs) which consist of a cation exchange layer (CEL) and anion exchange layer (AEL) are quite effective as membranes in gas phase electrolyzers. However, such membranes can also serve as a host to embed photocatalysts and electrocatalysts. By selectively exchanging cations with Cd2+ and anions with AuCl4–, we were able to synthesize CdS and Au nanoparticles in CEL and AEL layers, respectively, through sequential chemical and photocatalytic reactions. Reacting Cd2+ with thioacetamide formed the CdS nanoparticles in CEL. The photogenerated electrons from CdS were then used to reduce AuCl4– in an H-cell configuration to produce Au nanoparticles in AEL and thus prepare a photocatalytically active BPM film (referred to as a CdS/BPM/Au film). Such a concerted design of BPM allows “vectorial” electron transfer between two layers of BPM leading to its transfer to an acceptor molecule (methyl viologen) in solution. Designing photocatalytically active BPM and understanding the vectorial electron flow between two separate ion-selective layers offer new opportunities in water splitting and CO2 reduction.
Larger Picture of the work: Appropriate modifications of BPM can allow for MEA configuration based Carbonate electrolyzers in CO2 reduction.
Chhetri et. al JPC C (2021)
Producing value-added chemicals from waste CO2 gas
Cu is perhaps the only versatile element that is uniquely positioned for hydrocarbon (HCs) production through electrocatalytic CO2 reduction. While the product distribution can be optimized through the controlling Cu size, shapes, and valences [1-3], the intrinsic sluggish hydrogenation kinetics associated with Cu alone may rely on the metal alloying strategy to receive improvements [4]. Platinum group metals (PGMs) have a long history of being used as an effective species for hydrogen activation and spillover in various thermocatalytic reactions [5-6], but their utilization for CO2 electrocatalytic reaction to make HCs has not met with success. In the latter case, the hydrogen evolution reaction (HER) is the dominant major side reaction during CO2 reduction in the liquid-solid reaction environment, where the presence of PGM can easily let the HER supersede the hydrogenation of CO2 at relatively higher overpotential when high current density is anticipated for industrial relevant works. Moreover, to avoid shadowing the unique Cu catalysis for HCs formation and escalating the materials cost, a minimal amount of scarce PGMs shall be used, if indeed they can work with Cu for the targeted reaction. In this work, we report our design and synthesis of Cu-Pd1 and -Pt1 single-atom alloy (SAA) catalysts for facile CH4 and/ or C2H4 formation through electrocatalytic CO2 reduction. We show the high-surface-density PGMs that are otherwise highly active for H2 production as nanoparticles or clusters (with or without Cu), only at atomic dispersion, promote the hydrogenation of adsorbed intermediate on Cu surface and won’t be poisoned by the ubiquitous -CO reaction intermediates. With a trace amount of PGMs acting as the H* pump and the intact CO2 hydrogenation chemistry on Cu, consistent findings were made from SAAs with polycrystalline to facet-selective Cu morphologies, where targeted products such as CH4 or C2H4 can be selectively produced with appreciable current densities (220 mA/cm2).
Fabricating Metal/Metal hydroxide scalable electrodes for Hydrogen Production
Electrochemical dual-pulse plating with sequential galvanostatic and potentiostatic pulses has been used to fabricate an electrocatalytically active Ni/Ni(OH)2/graphite electrode. This electrode design strategy to generate the Ni/Ni(OH)2 interface on graphite from Ni deposits is promising for electrochemical applications and has been used by us for hydrogen generation. The synergetic effect of nickel, colloidal nickel hydroxide islands, and the enhanced surface area of the graphite substrate facilitating HO–H cleavage followed by H(ad) recombination, results in the high current density [200 mA/cm2 at an overpotential of 0.3 V comparable to platinum (0.44 V)]. The easy method of fabrication of the electrode, which is also inexpensive, prompts us to explore its use in fabrication of solar-driven electrolysis.
Significance: The successful utilization of solar energy to economically produce green fuel should involve facile and inexpensive means for electrolysis of water. To do so, it is necessary to replace the platinum catalyst with an in situ electrode fabrication process involving active catalyst with readily available materials. We have been successful in synthesizing an inexpensive Ni/Ni(OH)2/graphite electrode whose performance is as good as Pt. By a suitable choice of the relative proportion of Ni and Ni(OH)2, we obtain high current density at low overpotentials. The sequential galvanostatic and potentiostatic pulses used for the electrodeposition of Ni on the graphite rod provide control over the morphology and composition and the improved electrochemical performance
Chhetri et. al PNAS (2017)
in-situ studies of electrified interfaces during heterogenous catalysis
The understanding of exact timeline of chemical event happening at the interface of electrode-electrolyte under various applied controlled parameters can decipher the underlying mechanism of heterogenous catalysis. This can also help in modelling the structure-function-activity relationship. All these information can be intuitively used to scale up any electrolyzer performance leading to commercialization of the research output. We have been working on achieving this by our custom-built in-situ ATR-SEIRAS and in-situ Raman spectroscopy combining spectroscopy and electrochemistry. this project is under progress.
Splitting sea-water to render abundant hydrogen through water splitting using solar and renewable energy
Producing hydrogen from water in an efficient manner could significantly reduce consumption of fossil fuels. In this regard the abundant presence of water in oceans offers an important alternative approach for water splitting using seawater. Direct use of seawater for the generation of hydrogen is a difficult and complex process due to the presence of various ions in seawater, which affect the activity of the catalysts and makes the selectivity towards efficient water splitting a challenging task. Herein various ways are reported to efficiently reduce seawater to hydrogen under visible light irradiation by various catalysts already reported by this group. A better performance than pure water was observed in some cases, and in a few cases the opposite was observed, implying that with a proper approach seawater can be efficiently reduced to generate hydrogen.
Chhetri et. al. Adv Mater. (2016)
Chhetri et. al. Adv. Mater. (2019)
Dalton Trans. (2020)
Photoelectrochemical water splitting
Strategically integrating semiconducting films with an efficient water oxidation catalyst to reduce charge recombination and improve the photocurrent is the bottleneck in photoelectrochemical (PEC) water splitting. Amorphous catalysts, especially the mixed metal oxides/hydroxides, show better stability and activity because of their unique morphology. Facile, reproducible synthesis of these catalysts by a simple method has been problematic. In this Letter, we show for the first time the application of pulse plating to synthesize amorphous Co–La mixed double hydroxide (MDH) on BiVO4/FTO (FTO, flourine-doped tin oxide). The method provides better adhesion and uniform deposits with controlled composition and grain size and facilitates fast charge transport, while lowering the charge recombination at the interface of the electrolyte and the semiconductor. With respect to BiVO4, reduction in onset potential by 0.53 V as well as 2.7 and 33.4 times increment in photocurrent density (J) at 1.23 V and the lower potential 0.6 V, respectively, obtained by BiVO4/MDH is noteworthy. The results obtained here suggest the possibility of using BiVO4/MDH in PEC cells and photoelectrochemical diodes.
With the tactical integration of band edge energetics concepts in semiconducting films to reduce charge recombination and photocorrosion, an improvement in the photocurrent can be achieved by introducing CuO and NixPy into Cu2O films. Photodegradation limitations of Cu2O are overcome by the Cu2O–CuO–NixPy photocathode. NixPy, because of its excellent electrocatalytic hydrogen evolution activity, helps in obtaining better stability and activity. The individual effects of CuO and NixPy have been investigated and it is found that the activity enhancement stems mainly from the contribution of NixPy, whereas CuO helps with the unidirectional flow of photogenerated charges to prevent the photocorrosion of Cu2O. Relative to bare and modified Cu2O, Cu2O–CuO–NixPy shows a considerable reduction in the overpotential and a remarkable improvement in the photocurrent at 0 V (vs. RHE). This is the first report on the use of NixPy as the co-catalyst in a Cu2O based photocathode system to improve its photostability as well as its activity.
Chhetri et. al. ACS Energy Lett. (2017)
Chhetri et. al. PCCP (2018)
Chem. Eur. J (2019)