Photoelectrocatalytic Hydrogen Generation: Current Advances in Materials and Operando Characterization.

Photoelectrochemical (PEC) hydrogen generation is a promising technology for green hydrogen production yet faces difficulties in achieving stability and efficiency. The scientific community is pushing toward the development of new electrode materials and a better understanding of the underlying reactions and degradation mechanisms. Advances in photocatalytic materials are being pursued through the development of heterojunctions, tailored crystal nanostructures, doping, and modification of solid-solid and solid-electrolyte interfaces. Operando and in situ techniques are utilized to deconvolute the charge transfer mechanisms and degradation pathways. In this review, both materials development and Operando characterization are covered for advancing PEC technologies. The recent advances made in the PEC materials are first reviewed including the applied improvement strategies for transition metal oxides, nitrites, chalcogenides, Si, and group III-V semiconductor materials. The efficiency, stability, scalability, and electrical conductivity of the aforementioned materials along with the improvement strategies are compared. Next, the Operando characterization methods and cite selected studies applied for PEC electrodes are described. Operando studies are very successful in elucidating the reaction mechanisms, degradation pathways, and charge transfer phenomena in PEC electrodes. Finally, the standing challenges and the potential opportunities are discussed by providing recommendations for designing more efficient and electrochemically stable PEC electrodes.

Synthesis of a pillared graphene nanostructure: a counterpart of three-dimensional carbon architectures.

Graphene is a single sheet of carbon atoms with outstanding electrical and physical properties and is being exploited for applications in electronics, sensors, photovoltaics, and energy storage. A novel 3D architecture called a pillared graphene nanostructure (PGN) is a combination of two allotropes of carbon, including graphene and carbon nanotubes. A one-step chemical vapor deposition process for large-area PGN fabrication via a combination of surface catalysis and in situ vapor-liquid-solid mechanisms is described. A process by which PGN layers can be transferred onto arbitrary substrates while keeping the 3D architecture intact is also described. Single and multilayer stacked PGNs are envisioned for future ultralarge and tunable surface-area applications in hydrogen storage and supercapacitors.