A titanium carbide (Ti3C2Tx) MXene is employed as an efficient solid support to host a nitrogen (N) and sulfur (S) coordinated ruthenium single atom (RuSA) catalyst, which displays superior activity toward the hydrogen evolution reaction (HER). X‐ray absorption fine structure spectroscopy and aberration corrected scanning transmission electron microscopy reveal the atomic dispersion of Ru on the Ti3C2Tx MXene support and the successful coordination of RuSA with the N and S species on the Ti3C2Tx MXene. The resultant RuSA‐N‐S‐Ti3C2Tx catalyst exhibits a low overpotential of 76 mV to achieve the current density of 10 mA cm−2. Furthermore, it is shown that integrating the RuSA‐N‐S‐Ti3C2Tx catalyst on n+np+‐Si photocathode enables photoelectrochemical hydrogen production with exceptionally high photocurrent density of 37.6 mA cm−2 that is higher than the reported precious Pt and other noble metals catalysts coupled to Si photocathodes. Density functional theory calculations suggest that RuSA coordinated with N and S sites on the Ti3C2Tx MXene support is the origin of this enhanced HER activity. This work would extend the possibility of using the MXene family as a solid support for the rational design of various single atom catalysts.

Hydrogen production via photoelectrochemical water-splitting is a key source of clean and sustainable energy. The use of one-dimensional nanostructures as photoelectrodes is desirable for photoelectrochemical water-splitting applications due to the ultralarge surface areas, lateral carrier extraction schemes, and superior light-harvesting capabilities. However, the unavoidable surface states of nanostructured materials create additional charge carrier trapping centers and energy barriers at the semiconductor-electrolyte interface, which severely reduce the solar-to-hydrogen conversion efficiency. In this work, we address the issue of surface states in GaN nanowire photoelectrodes by employing a simple and low-cost surface treatment method, which utilizes an organic thiol compound (i.e., 1,2-ethanedithiol). The surface-treated photocathode showed an enhanced photocurrent density of -31 mA/cm at -0.2 V versus RHE with an incident photon-to-current conversion efficiency of 18.3%, whereas untreated nanowires yielded only 8.1% efficiency. Furthermore, the surface passivation provides enhanced photoelectrochemical stability as surface-treated nanowires retained ∼80% of their initial photocurrent value and produced 8000 μmol of gas molecules over 55 h at acidic conditions (pH ∼ 0), whereas the untreated nanowires demonstrated only <4 h of photoelectrochemical stability. These findings shed new light on the importance of surface passivation of nanostructured photoelectrodes for photoelectrochemical applications.

MXene, a new class of 2D materials, has gained significant attention owing to its attractive electrical conductivity, tunable work function, and metallic nature for wide range of applications. Herein, delaminated few layered Ti3C2Tx MXene contacted Si solar cells with a maximum power conversion efficiency (PCE) of ≈11.5% under AM1.5G illumination are demonstrated. The formation of an Ohmic junction of the metallic MXene to n+‐Si surface efficiently extracts the photogenerated electrons from n+np+‐Si, decreases the contact resistance, and suppresses the charge carrier recombination, giving rise to excellent open‐circuit voltage and short‐circuit current density. The rapid thermal annealing process further improves the electrical contact between Ti3C2Tx MXene and n+‐Si surface by reducing sheet resistance, increasing electrical conductivity, and decreasing cell series resistance, thus leading to a remarkable improvement in fill factor and overall PCE. The work demonstrated here can be extended to other MXene compositions as potential electrodes for developing highly performing solar cells.

The monolithic integration of photoelectrochemical solar energy conversion and electrochemical energy storage offers an efficient and compact approach toward practical solar energy utilization. This work presents the design principles for and the demonstration of a highly efficient integrated solar flow battery device with a record solar-to-output electricity efficiency. These results will enable a highly efficient approach for practical off-grid solar utilization and electrification.

3D organic–inorganic hybrid halide perovskites have attracted great interest due to their impressive optoelectronic properties. Recently, the emergence of 2D layered hybrid perovskites, with their excellent and tunable optoelectronic behavior, has encouraged researchers to develop the next generation of optoelectronics based on these 2D materials. However, device fabrication methods of scalable patterning on both types of hybrid perovskites are still lacking as these materials are readily damaged by the organic solvents in standard lithographic processes. We conceived the orthogonal processing and patterning method: Chlorobenzene and hexane, which are orthogonal to hybrid perovskites, are utilized in modified electron beam lithography (EBL) processes to fabricate perovskite-based devices without compromising their electronic or optical characteristics. As a proof-of-concept, we used the orthogonal EBL technique to fabricate a 2D layered single-crystal (C6H5C2H4NH3)2PbI4 photodetector featuring nanoscale patterned electrodes and superior photodetection ability with responsivity of 5.4 mA/W and detectivity of 1.07 × 1013 cm Hz1/2/W. Such orthogonal processing and patterning methods are believed to fully enable the high-resolution, high-throughput fabrication of complex perovskite-based electronics in the near future.

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Building on regenerative photoelectrochemical solar cells and emerging electrochemical redox flow batteries (RFBs), more efficient, scalable, compact, and cost-effective hybrid energy conversion and storage devices could be realized. An integrated photoelectrochemical solar energy conversion and electrochemical storage device is developed by integrating regenerative silicon solar cells and 9,10-anthraquinone-2,7-disulfonic acid (AQDS)/1,2-benzoquinone-3,5-disulfonic acid (BQDS) RFBs. The device can be directly charged by solar light without external bias, and discharged like normal RFBs with an energy storage density of 1.15 Wh L and a solar-to-output electricity efficiency (SOEE) of 1.7 % over many cycles. The concept exploits a previously undeveloped design connecting two major energy technologies and promises a general approach for storing solar energy electrochemically with high theoretical storage capacity and efficiency.

Sequestering CO2 in the form of carbon-based liquid fuels would provide both a convenient and sustainable form of energy for practical use as well as mitigate the effects of global warming and climate change.