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Formaldehyde is an essential building block for hundreds of chemicals and a promising liquid organic hydrogen carrier (LOHC), yet its indirect energy-intensive synthesis process prohibits it from playing more significant role. Here we report a direct CO reduction to formaldehyde (CORTF) process that hybridizes thermal and electro-catalysis and utilizes hydrogen underpotential deposition property to overcome thermodynamic barrier and scaling relationship restriction. Using molybdenum phosphide as catalyst, formaldehyde can be produced with nearly 100% Faradaic efficiency in aqueous KOH solution, with its formation rate being one order of magnitude higher compared with state-of-the-art thermal catalysis approach. Simultaneous tuning of current density and reaction temperature leads to more selective and productive formaldehyde synthesis, confirming the effectiveness of “hybrid” approach. DFT calculations reveal that desorption of *H2CO intermediate likely serves as rate-limiting step, and the participation of H2O turns the reaction into thermodynamically favorable. Furthermore, a full-cell reaction set-up was demonstrated with CO hydrogenation to HCHO being achieved without any energy input, which shows the spontaneous potential of the reaction. Our study shows the advantage of hybridizing thermal and electro-catalysis in realizing thermodynamics and scaling relation confined reaction, which could serve as a new strategy in future reaction design.

Introduction Oxygen reduction reaction (ORR) accounts for a substantial portion of the energy loss of the proton exchange membrane fuel cell system used for vehicle application. Current state of art ORR catalysts are typically Pt-alloy nanoparticles supported on carbon, of which surface Pt is solely the active site and their activity improvement is fundamentally limited by a “scaling relationship” [1]. In this study, we report the preparation of a SnOx/Pt−Cu−Ni heterojunctioned nanostructure as one potential strategy to break the scaling relationship in ORR. Experimental results confirm a significant activity enhancement compared with pristine Pt−Cu−Ni. Theoretical study suggests a dual-site cascade mechanism wherein the first two steps occur on SnOx sites, followed by transfer of the intermediate to adjacent Pt sites for the subsequent steps. This new catalyst design offers a plausible new approach to achieve high ORR activity on Pt alloys by introducing a second active site. Materials and Methods Pt−Cu−Ni alloy nanoparticles were synthesized by a solid-state chemistry method involving electrochemical treatment to generate a clean Pt surface prior to use in this study [2]. The as prepared Pt-Cu-Ni catalysts were first de-alloyed and then followed by immersion in SnCl2 solution for various time to coat with SnOx [3]. The resulting heterojunctioned catalysts were characterized by HR-TEM, XPS, XANES, as well as in electrochemical measurement to determine the activity and durability. The density functional theory (DFT) simulations were performed with the Quantum ESPRESSO package to calculate the energy states of reaction intermediates on different surface sites. Results and Discussion The conceptual design of the dual site catalyst, as shown in Figure 1(a). involves a possible migration of reaction intermediates during the steps of ORR. Such a migration should be driven by the difference in free energy of the sites. For proof-of-concept, we synthesized Pt−Cu−Ni nanoparticles and then deposited SnOx on the surface to form a heterojunctioned nanostructure (Figure 1(b)). SEM -EDX and XPS analyses confirmed that the SnOx content increased with deposition time, while the Pt:Cu:Ni ratio remained nearly unchanged before and after the deposition. XANES and high resolution XPS characterization suggest the oxidation state of the SnOx is primarily 4+. A decrease of electrochemical active surface area (ECSA) was observed as the deposition time (td) increases (Figure 1 (c)). The mass activity and specific activity (SA) both exhibit a volcano trend with respect to td with the highest values at td=5 min. The apparent SA increased by 40% as compared to the pristine Pt-Cu-Ni, and if only considering the interfacial sites, the estimated specific activity enhancement may be up to 10 folds (Figure 1(d)). While these results provide unambiguous experimental evidence of SnOx’s promoting effect, DFT simulation of the reaction pathways was performed to obtain insight into the possible mechanism (Figure 1(e)). The results suggest the SnOx and the neighboring Pt sites may have cooperated to find the most kinetically favored pathway (Figure 1(f)), wherein the O2 first protonated on SnOx sites to form *OOH and *O intermediates, and then the *O transfers to Pt sites to complete the remaining steps. Conclusion This study demonstrates a strategy to bypass the energy barrier bottleneck of ORR, providing one more dimension of design flexibility towards developing highly active electrode catalysts for fuel cell applications. References Kulkarni, A. et al., Chem. Rev. 2018, 118 (5), 2302−2312. Zhang, C. et al., J. Am. Chem. Soc. 2014, 136 (22), 7805−7808. Shen, X. et al., J. Am. Chem. Soc. 2019, 141(24), 9463-9467. Figure 1

A reliable clean water supply is now one important and challenging issue for the human society. With the facts that only 0.4% of the water on earth is readily drinkable and 98% of the water is saltwater, water desalination for clean water production has become a key strategic solution to satisfy the increasing global water demand. Over the years, different saltwater desalination technologies were researched and developed, including reverse osmosis membrane desalination (RO), electrodialysis (ED), capacitive desalination (CDI) and multi-effect distillation (MED). However, some inherent technical issues, like high operation cost, large capital cost and/or low desalination capacity, associate with these existing technologies that lead to a high clean water production cost and limit their applications. Thus, there is a need of new water desalination technology that can purify saltwater with low cost and high efficiency. In this work we report a new water-soluble nickel phthalocyanine tetrasulfonic acid tetrasodium salt (NiPcTATS)-based redox flow desalination battery (RFDB) for safe, effective and efficient water-salt separation. The fabricated RFDB cell exhibited a high desalination rate at 3.4 gNaCl/(molNiPcTATS∙hr) even with a low 0.5 V cell voltage and required as low as 11.5 kJ/mol salt in energy consumption. The cell showed excellent reversibility and durability for long-term operation, benefiting from the fast-redox kinetics and chemical stability of the redox couple. With no consumption of the redox couple and energy recovery during the salination process, this new method provides a continuous desalination capability with unlimited salt removal capacity. We also demonstrated the use of simple solar panel for effectively driving the RFDB cell, proving it a promising and practical technology for clean water production in remote places like islands and ships.

Material novelty is momentous for electrocatalyst in striding into a renewable energy era. Oxygen evolution reaction (OER) is of great significance for hydrogen production via water electrolysis, but has a high energy barrier that limits the energy conversion efficiency. Herein we report a highly-efficient and long-term durable NiFePB OER electrocatalyst, which composes of unique porous amorphous conductive solids with finely tuned nonmetal elements. The NiFePB phase formation is confirmed with X-ray absorption spectroscopy (XAS) and X-ray photoelectron spectroscopy (XPS). X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM) characterizations determine a porous amorphous structure. The outstanding metallic conductivity and corrosion resistance properties are simulated with density functional theory (DFT) calculations. Benefiting from these unique features, the NiFePB exhibits an extraordinarily low overpotential of 197 mV to reach an OER current density of 10 mA/cm2 and 233 mV to reach 100 mA/cm2 under chronopotentiometry condition, with the Tafel slope harmoniously conforming to 34 mV/dec. The catalyst also has an impressive long-term stability, evidenced by a limited activity decay for more than 50-h in a wide current density range from 10 to 200 mA/cm2. This work strategically directs a way for heading up a promising energy conversion alternative.