DFT calculations: A powerful tool for better understanding of electrocatalytic oxygen reduction reactions on Pt-based metallic catalysts

Solar-induced overall water splitting to produce hydrogen is inspiring towards energy sustainability, but it is also formidable due to its limited efficiency seriously hindering its scale up for practical application. CdS is an important transition metal sulfide with low-work-function. However, its photostability is often deteriorated due to photocorrosion influence. To overcome this issue, single-atom Pd was employed here to decorate CdS to form a CdS-Pd nanocatalyst through a simple and controllable photoinduced reduction strategy. The synergetic semiconductor (CdS)-metal (Pd) interaction promotes the fast bulk-to-surface electron migration, thereby the resultant CdS-Pd (3.83‰) nanocatalyst shows considerable structural stability and dramatically improved solar-induced HER activity in overall water splitting, about 110-fold higher than that of pristine CdS. Meanwhile, high apparent quantum yields (AQYs) of 4.47%/1.81% and 33.92%/27.49% were respectively achieved with this decorated nanocatalyst under the light of 420 nm/500 nm in absence and presence of scavenger, demonstrating the high-efficiency under broadband light illumination. Density functional theory (DFT) calculation supports that the easy formation of H* intermediates on the decorated nanocatalyst due to low energy barriers accounts for the internal promoted mechanism for hydrogen production. This study provides important insight to gain stable CdS-based photocatalysts for high-efficient hydrogen production by overall water splitting. 

Pd single-atom decorated CdS nanocatalyst for highly efficient overall water splitting under simulated solar light

An account of the strategies to enhance the water splitting efficiency of noble-metal-free electrocatalysts

In situ electrochemical reduced Au loaded black TiO2 nanotubes for visible light photocatalysis

Defective carbon-based materials (DCMs) have recently been considered as one of the most promising alternatives to precious metal electrocatalysts owing to their irreplaceable advantages, such as environmentally friendly, low cost and high structural tunability. Despite remarkable progress has been achieved, grand challenges of their further development are still remained by the traditional “trial-and-error” approaches, mainly due to the lack of precise synthetic methodologies as well as in-depth understandings of active centers and underlying electrocatalytic mechanisms. Herein, this review will provide a comprehensive overview and perspective on the critical issues and possible solutions regarding the controllable synthesis of DCMs, with special emphasis on the theoretical guidance in designing complex carbon defect structures and operando characterizations in exploring “dynamic” active centers. More importantly, it will also highlight recent advances in the applications of DCMs for the cutting-edge “E-Refinery”, focusing on the electrochemical conversion of electricity into fuels and chemical building blocks (e.g., H2, O2, CH4, C2H4, CH3OH, C2H5OH, NH3 and other organic compounds). Finally, further challenges and opportunities are summarized to shed some light on the unexploited area and future directions in expectation of stimulating the broad interest of interdisciplinary researchers.

Defective carbon-based materials: controllable synthesis and electrochemical applications

Photocatalysis is a promising technology for energy and environment applications. Herein, a dual-defect heterojunction system of TiO2 hierarchical microspheres with oxygen vacancies modified with ultrathin MoS2−x nanosheets (MoS2−x @TiO2-OV) is designed for simultaneously degrading pollutants and evolving hydrogen. MoS2−x @TiO2-OV exhibits a dramatically enhanced photocatalytic activity with a H2 evolution rate of 2985.16 μmol g−1h−1. In treating the simulated pharmaceutical wastewater, MoS2−x @TiO2-OV is capable of purifying various refractory contaminants, with the highest H2 evolution rate of 41.59 μmol g−1h−1 during enrofloxacin degradation. While treating the simulated coking wastewater, the catalyst achieves a H2 evolution rate of 102.72 μmol g−1h−1 and a mineralization rate of 50%. Computational studies suggest that the dual-defect is superior for the adsorption of H* and producing·OH (‘dual-defect boosted dual-function’). Also, the dual-defect sites significantly boosted the charge-carrier separation and transfer efficiencies. This work highlights the crucial role of defect engineering to develop the energy-recovering wastewater treatment approaches.

Photocatalytically recovering hydrogen energy from wastewater treatment using MoS2 @TiO2 with sulfur/oxygen dual-defect

Exploring a novel approach for the synthesis of oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER) catalysts with inexpensive and high-activity is desirable. Herein, we report a bubble templating method to synthesize the graphene-like mesoporous carbon sheets with point defects as ORR/HER bifunctional electrocatalysts. The typical product shows excellent ORR performance including the positive onset potential (740 mV) and high diffusion-limiting current density (4.07 mA cm−2). Along with small Tafel slopes, the overpotential is determined to be about −453 and −378 mV at 10 mA cm−2 in both alkaline and acidic media, which suggests a good candidate for HER reaction as well. The superior catalytic activities are derived from the abundant point defects on the mesoporous carbon sheets surface, especially the existence of pyridinic and pyrrolic nitrogen species. This study may be an alternative route to prepare the novel functional materials for the applications of ORR and HER.

Xiaotao Chen

Papers

Photocatalytically recovering hydrogen energy from wastewater treatment using MoS2 @TiO2 with sulfur/oxygen dual-defect

Point-Defect-Rich Carbon Sheets as the High-Activity Catalyst Toward Oxygen Reduction and Hydrogen Evolution