As a promising alternative hydrogen evolution electro-catalyst to platinum, a classical and earth-abundant "titania" is investigated. Herein, the paradigm of electroinactive titania has been surmounted by exploiting defect engineering as a tool, which tailors the local atomic structure of nonconductive titania via electrochemical cathodization strategy. The enhanced electro-conducting properties along with favorable surface energetics for H ads of reduced titania (TiO 1.23 ) ensures ultrafast HER kinetics. Because of the proximity with the benchmark Pt, the reduced titania exhibits excellent HER catalytic activity in an acidic electrolyte by exhibiting low onset potential of 75 mV versus RHE and a Tafel slope of 88 mV•dec −1 , and it demonstrates 10 mA•cm −2 at a potential of 198 mV versus RHE. Furthermore, the cathodization process also endows "magic effects" by effectively exposing the (111) close-packed plane with extravagant texture coefficient and makes the structure more thermodynamically stable. The longterm durability studies (5000 cycles of cyclic sweeping, 40 h of static polarization) confirm the extremely stable HER catalytic activity of TiO 1.23 . These findings suggest that by tuning oxygen vacancies in the lattice and its concomitant cumulative strained configuration, reduced titania can be an effective HER electro-catalyst for electrochemical water splitting.

The energy crisis is one of the most serious issue that we confront today. Among different strategies to gain access to reliable fuel, the production of hydrogen fuel through the water-splitting reaction has emerged as the most viable alternative. Specifically, the studies on defect-rich TiO2 materials have been proved that it can perform as an efficient catalyst for electrocatalytic and photocatalytic water-splitting reactions. In this invited review, we have included a general and critical discussion on the background of titanium sub-oxides structure, defect chemistries and the consequent disorder arising in defect-rich Titania and their applications towards water-splitting reactions. We have particularly emphasized the origin of the catalytic activity in Titania-based material and its effects on the structural, optical and electronic behavior. This review article also summarizes studies on challenging issues on defect-rich Titania and new possible directions for the development of an efficient catalyst with improved catalytic performance.

To gain constructive insight into the possible effect of doping on the electrocatalytic activity of materials, a catalytic framework with a discrete distribution of dopants is an appropriate model system. Such a system assures well-defined active centers, maximum atom utilization efficiency, and hence enhanced selectivity, catalytic activity, and stability. Herein, a comprehensive investigation of the electrocatalytic activity of iron-doped cobalt oxide (Fe–Co3O4) nanosheets is presented. In order to understand the contribution of dopants, a series of materials with controlled doping levels are investigated. By controlled iron inclusion into the structure of Co3O4, an apparent improvement in the oxygen evolution reaction activity which is reflected in the decrease of 160 mV in the overpotential to reach the current density of 10 mA/cm2 is manifested. Additionally, it is shown that there exists an optimum doping content above which the catalytic activity fades. Further investigation of the system with density functional calculations reveals that, along with the optimization of adsorption energy toward the reaction intermediates, substantial downshift of the Fermi level and delocalization of electron density occurs on introducing iron ions into the structure.

As an attempt to explore the instantaneous changes that occur in titania during the cathodization process, herein we employ electron paramagnetic resonance (EPR) operando spectroscopy throughout the cathodization. This insitu probing facilitates an experimentally verifiable clue about the underlying active sites in the highly active catalyst (TiO 1.23 ) resulting from the cathodization. Furthermore, this study correlates the evolution of cathodization-driven defects and the resultant polaronic motion with hydrogen evolution reaction (HER). The defect richness and structural diversity in the reduced titania attribute 'magic effects' on its charge carrier dynamics and activity. Also, the enhanced electrocatalytic activity of TiO 1.23 is explained in terms of its orbital reconstruction, electronic and structural modifications. Moreover, work function measurements reveal shifting of Fermi level toward the conduction band by defect-mediated Urbach tail and bound excitonic emissions, in line with the findings based on EPR spectroscopy. The observed phenomenon in TiO 1.23 is further validated by its high (negative) surface charge, enhanced hydrophilicity and surface roughness compared with native TiO 2 . Therefore, these studies are earmarked for deep insight into the electronic structure modification of titania during the cathodization process and also provide a better understanding of the HER process that occurred in TiO 1.23 .

No abstract

The design of new and improved catalysts is an exciting field and is being constantly improved for the development of economically, highly efficient material and for the possible replacement of platinum (Pt)-based catalysts. In this, carbon-based materials play a pivotal role due to their easy availability and environment friendliness. Herein, we report a simple technique to synthesize layered, nitrogendoped, porous carbon and activated carbons from an abundant petroleum asphaltene. The derived nitrogen-doped carbons were found to possess a graphene-like nanosheet (N-GNS) texture with a significant percentage of nitrogen embedded into the porous carbon skeleton. On the other hand, the activated porous carbon displayed a surface area (SA) of 2824 m 2 /g, which is significantly higher when compared to the nitrogen-doped carbons (SA of ∼243 m 2 /g). However, the nonactivated N-GNS were considered as an attractive candidate due to their high electrochemical active surface area, the presence of a mixture of porous structures, uniform layers, and effective doping of nitrogen atoms within the carbon matrix. Importantly, the hydrogen evolution reaction activity of the derived N-GNS sample illustrates a significant catalytic performance when compared to that of other nonfunctionalized carbons. Our current finding demonstrates the possibility of converting the asphaltene wastes into a highvalue-functionalized porous carbon for catalytic applications.

Studies on intercalation or substitution of atoms into layered two-dimensional (2D) materials are rapidly expanding and gaining significant consideration due to their importance in electronics, catalysts, batteries, sensors, etc. In...

No abstract