The intrinsic activity of catalysts is crucial for the electrocatalytic hydrogen evolution reaction, which is essentially dependent on their crystal structure and surface electronic state. The variable crystalline phase in tungsten oxide (WO 3 ) can provide a favorable opportunity for modulating surface electronic state. In this work, the structure−activity relationship of the representative hexagonal and monoclinic phase WO 3 (h-WO 3 and m-WO 3 ) for the hydrogen evolution reaction was discussed in detail by experimental techniques combined with density functional theory (DFT) calculations. DFT calculations reveal that m-WO 3 exhibits the modest H-adsorption/desorption energy, which is beneficial to the fast desorption of active H* intermediate compared to h-WO 3 , displaying superior catalytic activity in the hydrogen evolution reaction. To accelerate the charge transfer, introduction of reduced graphene oxide (rGO) further amplifies the intrinsic catalytic activity endowed with this crystalline phase. In acid media, the m-WO 3 /rGO catalyst shows a low Tafel slope of 32 mV dec −1 , requires an overpotential of only 35 mV to drive a current density of 10 mA cm −2 , and keeps excellent stability during accelerated durability test. This work presents significance of crystalline phase for optimizing the intrinsic activity of catalyst and provides a novel idea to design a high-efficient catalyst for the hydrogen evolution reaction.

Electrocatalytic water splitting involving the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is a crucial and effective pathway to obtain clean and renewable energy resources. The advanced electrocatalysts can significantly reduce the reaction energy barrier to realize high‐efficiency energy conversion. In this regard, noble‐metal catalysts display excellent catalytic performance for the water splitting reaction, but the high cost hinders its large‐scale application. As a low‐cost candidate for noble‐metal catalysts, tungsten oxide is endowed with the variable crystalline phase and adjustable composition, which provide more opportunities to achieve satisfactory catalytic activity by engineering crystal structure and modulating surface electronic states. To promote the reaction activity and stability, some effective strategies have been developed to optimize the surface crystal and electronic structure of tungsten oxide electrocatalysts for overall water splitting. In this review, we especially highlight the latest advances and progress in the exploration of tungsten oxide electrocatalysts for HER and OER, and systematically classify these strategies into several design principles involving adjustable surface morphology, engineering defects, and synergistic catalysis, providing a deep understanding of the relationship between the catalytic activity and crystal structure in the tungsten oxide. Some perspectives are also proposed to guide a rational design of tungsten oxide electrocatalyst for water splitting.

Tungsten oxide (WO3) is an appealing electrocatalyst for the hydrogen evolution reaction (HER) owing to its cost‐effectiveness and structural adjustability. However, the WO3 electrocatalyst displays undesirable intrinsic activity for the HER, which originates from the strong hydrogen adsorption energy. Herein, for effective defect engineering, a hydrogen atom inserted into the interstitial lattice site of tungsten oxide (H0.23WO3) is proposed to enhance the catalytic activity by adjusting the surface electronic structure and weakening the hydrogen adsorption energy. Experimentally, the H0.23WO3 electrocatalyst is successfully prepared on reduced graphene oxide. It exhibits significantly improved electrocatalytic activity for HER, with a low overpotential of 33 mV to drive a current density of 10 mA cm−2 and ultra‐long catalytic stability at high‐throughput hydrogen output (200 000 s, 90 mA cm−2) in acidic media. Theoretically, density functional theory calculations indicate that strong interactions between interstitial hydrogen and lattice oxygen lower the electron density distributions of the d‐orbitals of the active tungsten (W) centers to weaken the adsorption of hydrogen intermediates on W‐sites, thereby sufficiently promoting fast desorption from the catalyst surface. This work enriches defect engineering to modulate the electron structure and provides a new pathway for the rational design of efficient catalysts for HER.

Solid chemicals MgCO 3 / Mg(OH) 2 (MgCO 3 ) 4˙5 H 2 O were selected to facilitate CO 2 absorption with MEA solvent. The catalytic carbamate formation was confirmed here, to verify heterogeneous catalysis. Since the aqueous hydroxide [OH -] can serve homogeneous catalyst of carbamate formation, MgCO 3 can serve as heterogeneous catalysts/promotors implemented for CO 2 absorption in the amine scrubbing process. The solid MgCO 3 accelerate the CO 2 absorption in MEA solvent properly. These solid chemicals proved to be good candidates for heterogeneous catalytic CO 2 absorption with amine.

Abstract. The CO 2 desorption analyses of amines were performed to reveal the behaviour of amine regeneration process. A typical primary amine (MEA) and two other secondary amines (MMEA and DEA) were selected in preparation for amine solutions under different concentrations, from 1-7 mol/L. The regeneration curves were plotted to describe the process. It was discovered that the specific CO 2 loading (mol/mol) that distinguish the amine regeneration curves into different regions were the same for the specific amine, despite different concentrations. These points were defined as "turning points" on regeneration curves. The turning points of MEA, MMEA and DEA are located at CO 2 loading of 0.40 mol/mol, 0.38 mol/mol and 0.28 mol/mol, respectively. The regeneration tests compared the relative heat duty at the first 2 hours: MMEA > MEA > > DEA.