Generation of hydrogen fuel via electrochemical water splitting powered by sustainable energy, such as wind or solar energy, is an attractive path toward the future renewable energy landscape. However, current water electrolysis requires desalinated water resources, eventually leading to energy costs and water scarcity. The development of cost‐effective electrocatalysts capable of splitting saline water feeds directly can be an evident solution. Herein, a surface reconstructed nickel‐iron layered double hydroxide (NF‐LDH) is reported as an exceptionally active and durable bifunctional electrocatalyst for saline water splitting without chloride corrosion. The surface reconstructed NF‐LDH consists of Ni3Fe alloy phase interconnected in a 2D network in which an ultrathin (≈2 nm) and low‐crystalline NiFe (oxy)hydroxide phase are formed on the surface. The NiFe (oxy)hydroxide phase draws large anodic current densities, satisfying the level of practical application, while the Ni3Fe alloy phase is simultaneously responsible for the high catalytic activity for cathodic reactions and superior corrosion resistance. The surface reconstructed NF‐LDH electrode can be easily fabricated in a large electrode area (up to 25 cm2) and can successfully produce hydrogen fuels from saline water powered by the laboratory‐made low‐intensity photovoltaic cell.

Recently, a low bandgap donor named poly[4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b:4,5-b ′ ]dithiophene-2,6-diyl-alt-(4-(2-ethylhexyl)-3-fluorothieno[3,4b]thiophene-)-2-carboxylate-2-6-diyl)]- (PTB7-Th-) based organic photovoltaic (OPV) devices has exhibited interesting behavior when tested under indoor light. Theoretically, a PTB7-Th : [6,6]-phenyl-C71-butyric acid methyl ester (PC70BM) active layer-based OPV can show >23% power conversion efficiency (PCE) under light-emitting diode (LED) light. However, to date, the experimentally achieved PCE (~11.63%) is significantly lower than the theoretical one. Therefore, we design an indoor OPV having PTB7-Th : PC70BM active layer and low-acidic and cheaper polypyrrole : polystyrene sulfonate (PPY : PSS) as the hole transport layer (HTL), by optimizing active layer thickness and processing conditions (spin coating speed and doping concentration) of the HTL via optical simulations and experiments. The results show that the device having 100 nm thick active layer and a PPY : PSS-based HTL (PPY : PSS; weight ratio between PPY and PSS 1 : 2) coated at 5000 rpm can exhibit a record high PCE value (16.35%) during its operation under 1000 lx LED lamp. In comparison, a commercially available PEDOT : PSS-based OPV can achieve maximum 14.21% PCE under the same conditions.

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