Gupta, Prashant

Hydrogen is a vital and significant alternative fuel that can play a major role in reducing the impact of climate change. Developing robust and highly active bifunctional catalysts is essential for achieving sustainable electrolytic hydrogen generation. The electrocatalysts used for the OER (oxygen evolution reaction) and HER (hydrogen evolution reaction) are prone to corrosion, particularly under alkaline conditions. Developing engineering solutions to provide stability while maintaining activity of RuO2 as a bifunctional catalyst remains a significant and major problem. In this study, we present a hierarchical heterostructure synergy effect that was generated through a straightforward electrode fabrication method, as opposed to a highly intensive and extremely challenging chemical synthesis route where heat-treated α-MnO2 (referred to as 400-α-MnO2) is used as an interlayer for RuO2. With the help of detailed EIS and XPS analysis, we observed that the presence of 400-α-MnO2 creates an unobstructed channel for electron transfer to RuO2, resulting in improved activity towards both the OER and HER, as well as increased durability. The heterojunction catalyst has also been evaluated in an AEM-based full cell, which exhibits remarkable stability and activity with a minimal RuO2 mass loading of 189 μg cm−2. The proposed engineered interface, using 400-α-MnO2, surpasses the stability and activity limitations of RuO2 in an alkaline environment.

Significant efforts are underway to enhance the efficiency of water electrolysis for sustainable hydrogen production. Approaches that were explored are the design of an efficient anode, engineering of electrolytes, and application of diffusion protective layer over the catalyst to protect it from corrosive reactions. Here we are exploring the engineering of electrode fabrication to enhance the efficacy of anode catalysts by ensuring that the materials are carefully selected. β-MnO2 has been used to develop a cost-effective method for electrode fabrication that establish a Schottky junction at heterostructure interface. This method transforms commercial RuO2, which is considered to be less active and stable, highly selective for chlorine oxidative reactions, into a highly active, stable, and OER-selective in alkaline medium and surrogate seawater. With the help of thorough electrochemical techniques, we found that this engineering significantly improves the effective electrochemical surface area, and higher kinetics and conversion per unit site, profoundly affecting the charge transfer mechanism and optimizing the adsorption of OER intermediates, resulting in much-increased mass activity. It is observed that the selectivity of the OER was enhanced due to the Lewis acid repercussions of β-MnO2.

Seawater seems to be a sustainable feed for hydrogen generation through electrolysis. Despite the thermodynamic propensity for the oxygen evolution reaction (OER) at the anode during seawater electrolysis, the kinetically fast and unfavorable chlorine oxidation reaction (COR) dominates. Thus, designing active and selective anodes for seawater electrolysis is challenging. Here, we are investigating the effect of MnO2 polymorphic structures as an anode material for simulated seawater electrolysis in a basic medium. Contrary to the belief that MnO2 is an OER catalyst, we discovered that only α- and β-MnO2 are preferentially OER catalysts, whereas γ- and δ-MnO2 are selective for COR. The experimental findings imply that discrete translational symmetry in distinct polymorphs promotes different reaction intermediates, disrupting the scaling relation between the OER and COR. We also studied the polymorphic impact of MnO2 on limiting Cl- ion transport over a conventional catalyst of IrO2 in an alkaline medium to scale up seawater electrolysis. The research found that γ-MnO2 is the most likely to impede the COR active sites over IrO2 among the four polymorphs studied (α-, β-, γ-, and δ-MnO2). We identified that γ-MnO2 functions as a Lewis acid layer, thereby augmenting the kinetics of the OER across the IrO2 surface and establishing a barrier against Cl- ions.

The hydrophilic–superhydrophilic transition dynamics of water on the multifunctional nanoporous anodic alumina (NAA) membranes of various pore lengths (0.03–5 μm) fabricated by the acid anodization process is demonstrated. The original pristine alumina surfaces were found to be in the hydrophilic Wenzel state. The pristine NAA sample surfaces were modified to a superhydrophilic state upon UV-ozone (UVO) exposure for 1 min. The sample surfaces were also modified to the near-superhydrophilic state by Argon plasma (Ar–P) treatment for 1 min. Carboxylate ions incorporated inside the NAA matrix during the anodization process were found to play an important role in modifying the sample surfaces to be superhydrophilic. It was revealed from XPS analysis that the increment in the oxygen percentage and reduction in the carbon percentage were the key points behind the superhydrophilic state after UVO and Ar–P treatment. The NAA matrix was made functional as a nanofluidic system consisting of water after UVO and Ar plasma exposure which can be used for micro-cooling, sensing, and filtering applications. Reversible switching to hydrophilic state was found, leaving the sample surfaces to ambient after UVO and Ar–P exposure.

Water electrolysis is a more sustainable way to produce green hydrogen than steam methanol reforming or coal gasification. Its efficiency is limited by slow oxygen evolution processes at the anode. Highly effective anodic electrocatalysts are difficult to produce. Layered double hydroxide is a promising and thoroughly researched OER material, however, long-term stability issues arise. In this study, we examine the modification of the electronic structure of NiMn LDH through the introduction of Ce doping. The analysis of the material using XPS and XRD indicates that Ce is effectively integrated into the NiMn crystal structure, resulting in lattice distortion and alterations to the electronic structure when doped at concentrations of up to 5%. Furthermore, various electrochemical characterizations indicated that Ce doping increased the number of electrochemically active sites, improved electronic conductivity, and optimized the electrochemical kinetics. The 5% Ce-doped NiMn LDH demonstrated a current density of 30 mA/cm2 at an overpotential of 561 mV, which is significantly lower than the 638 mV overpotential observed for NiMn LDH and considerably superior to that of commercial RuO2. The system exhibited complete stability throughout a 15-h operational duration at a consistent applied current density of 15 mA/cm2, with no indications of degradation observed.

The instability of hybrid organic–inorganic perovskites (HOIPs) in several electrolytes and the toxicity of heavy metals such as lead hinder their application in many electrochemical devices. Herein, an already existing Ruddlesden–Popper (R–P) structure of tungstic acid variants as a generic framework to achieve ultrastable HOIPs, serving as stable and safer alternatives to lead-based HOIPs in aqueous electrochemical devices, is introduced. An enormous improvement (of the tungsten-based framework) in electrochemical performance is achieved by converting electrochemically sluggish H2W2O7 to oxygen-deficient H2W2O7−δ to leverage a facile and reversible W6+→ W5+ transition along with local defect-mediated H+ insertion/extraction. This local structural modification results in a remarkable pseudocapacitive performance (specific capacitance of ≈622 F g−1 or specific capacity 155.5 mAh g−1 at 64 C) with no observable capacity fade (≈100% specific capacity retention after thousands of cycles) in 0.5 m H2SO4 aqueous solution. To extend the scope of utilization of this R–P phase in aqueous electrochemical energy storage devices, OA2W2O7−δ (OA = octylammonium), a HOIP, which similarly displays impressive EES performance is synthesized. Most importantly, when used as an electrode material, this HOIP exhibits remarkably high stability in aqueous acidic electrolyte. © 2025 Elsevier B.V., All rights reserved.