Kuei-Hsien Chen

In this work, we study the effect of sputtering pressures on the thermoelectric properties of GeTe films. The working pressures were differentiated from 3 to 30 mTorr, and the as-deposited films were annealed at 623 K for 10 min in Ar atmosphere. The results show that the working pressure has a significant effect on the Ge content and crystalline size. The turning trend of the Seebeck coefficient with different sputtering pressures corresponds to the Ge content. The surface morphology of annealed film will change from cracks to voids with increasing sputtering pressure. This behavior can be explained by the growth mechanisms model. The voids and relatively low crystalline size of GeTe films affect to the reduction of the electrical conductivity. In addition, the void content decreased as film thickness was increased. Therefore, controlling the working pressures in the sputtering process and film thickness is important for the thermoelectric performance of GeTe thin film. In our work, we prove that the thermoelectric properties of GeTe films could be optimized effectively by simply tuning different sputtering conditions.

Although hematite (i.e., α-Fe2O3) has been widely investigated in photoelectrochemical water oxidation studies due to its high theoretical photocurrent density, it still suffers from serious surface charge recombination and low photoelectrochemical stability. Here we report an in-situ electrochemical method to form a uniform and ultrathin (i.e., 3–5 nm) passivation layer all over the porosities of the optimized ~3.2% Ti-doped α-Fe2O3 photoanode. We unveil the amorphous and defective nature of the in-situ derived layer assigning to a high concentration of oxygen vacancy and intercalated potassium atoms there, i.e., the formation of Ti/K co-doped defective α-Fe2O3-x. Owing to the efficient passivation of surface states, alleviated surface-potential fluctuations, and low charge-transfer resistance at the interface, photoanodes show an average of ~60% enhancement in the photoelectrochemical performance, applied bias absorbed photon-to-current efficiency of 0.43%, and Faradaic efficiency of ~88%. Moreover, the passivation layer prevents direct contact between the electrode material and electrolyte, resulting in less degradation and outstanding photoelectrochemical stability with photocurrent retention of ~95% after ~100 hours, albeit by performing several successive in-situ electrochemical passivation processes. This work presents an industrially scalable method to controllably engineer the interfaces of semiconductors–electrolytes with precious metal-free defective hematite-based co-catalysts for sustainable photoelectrochemical solar-to-fuel conversion applications.

The quest of earth-abundant bifunctional electrocatalysts for highly efficient oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) is essential for clean and renewable energy systems. Herein, directed by the experimental analysis, we demonstrate layered nickel lithium phosphosulfide (NiLiP2S6) crystal as a highly efficient water-splitting catalyst in alkaline media. With strained lattice due to stacked layers as observed by TEM and electronic structure analysis performed by XPS showed mixed Ni2+,3+ oxidation states induced by addition of Li as a cation, NiLiP2S6 displays excellent OER (current density of 10 mA cm–2 showed an overpotential of 303 mV vs. RHE and a Tafel slope of 114 mV dec–1) and HER activity (current density of −10 mA cm–2 showed an overpotential of 184 mV vs. RHE and a Tafel slope of 94.5 mV dec–1). Finally, an alkaline media was employed to demonstrate the overall water splitting using NiLiP2S6 as both the anode and the cathode, which attained a 50 mA cm−2 current density at 1.68 V. This bimetallic phosphosulfide, together with long-term stability and enhanced intrinsic activity, shows enormous potential in water splitting applications.