Construction of N-doped carbon frames anchored with Co single atoms and Co nanoparticles as robust electrocatalyst for hydrogen evolution in the entire pH range

The development of low-cost, efficient, and high atomic economy electrocatalysts for hydrogen evolution reaction(HER) in the entire p H range for sustainable hydrogen production is of great importance but still challenging. Herein, we synthesize a highly dispersed N-doped carbon frames(NCFs) anchored with Co single atoms(SAs) and Co nanoparticles(NPs) catalyst by a doping-adsorption-pyrolysis strategy for electrocatalytic hydrogen evolution. The Co SAs-Co NPs/NCFs catalyst exhibits an excellent HER activity with small overpotential, low Tafel slope, high turnover frequency as well as remarkable stability. It also exhibits a superior HER performance in the entire p H range. Combining with experimental and theoretical calculation, we find that Co SAs with Co-N_(3) coordination structure and Co NPs have a strong interaction for promoting synergistic HER electrocatalytic process. The H_(2)O molecule is easily activated and dissociated on Co NPs, while the generated H^(*) is easily adsorbed on Co SAs for HER, which makes the Co SAs-Co NPs/NCFs catalyst exhibit more suitable H adsorption strength and more conducive to the activation and dissociation of H_(2)O molecules. This work not only proposes a novel idea for constructing coupling catalyst with atomic-level precision, but also provides strong reference for the development of high-efficiency HER electrocatalysts for practical application.

原子钼催化剂配位结构的动态演变促进氢分子在浆态床加氢裂化过程中的高效活化

开发具有高原子利用率和高转化频率的高效催化剂,用于减压渣油浆态床加氢裂化过程中H2分子的活化至关重要.本文采用“聚合-热解-原位硫化”策略,首次报道了一种高效稳定的单原子钼催化剂用于减压渣油浆态床加氢裂化反应,并发现了单原子Mo活性位点的原子配位结构动态演化机制.在VR加氢裂化过程中,与Mo配位的O原子逐渐被S原子取代,从而导致O/S交换过程.单原子钼的配位结构从反应前的Mo-O3S1演变为反应后的Mo-O1S3配位构型,有效促进了H2分子均裂活化为H自由基物种.所演变的单原子钼催化剂表现出优异的催化加氢活性和循环稳定性,其对减压渣油的单程转化率为65 wt.%,轻油收率为93 wt.%,焦炭产率仅为0.63 wt.%,按照所有金属计算的转化频率为0.35 s^(-1).理论计算表明,H2相互作用前后Mo 4d占据态的显著变化与单原子钼催化剂结构的动态演变有直接关系,并且Mo-O1S3位点较低的d带中心表明原子H扩散容易,有利于催化加氢.本文研究结果对于开发高原子经济性催化剂用于重油改质技术的工业应用具有重要意义.

Reaction environment self-modification on low-coordination Ni^(2+)octahedra atomic interface for superior electrocatalytic overall water splitting

Large scale synthesis of high-efficiency bifunctional electrocatalyst based on cost-effective and earth-abundant transition metal for overall water splitting in the alkaline environment is indispensable for renewable energy conversion.In this regard,meticulous design of active sites and probing their catalytic mechanism on both cathode and anode with different reaction environment at molecular-scale are vitally necessary.Herein,a coordination environment inheriting strategy is presented for designing low-coordination Ni^(2+)octahedra(L-Ni-8)atomic interface at a high concentration(4.6 at.%).Advanced spectroscopic techniques and theoretical calculations reveal that the self-matching electron delocalization and localization state at L-Ni-8 atomic interface enable an ideal reaction environment at both cathode and anode.To improve the efficiency of using the self-modification reaction environment at L-Ni-8,all of the structural features,including high atom economy,mass transfer,and electron transfer,are integrated together from atomic-scale to macro-scale.At high current density of 500 mA/cm2,the samples synthesized at gram-scale can deliver low hydrogen evolution reaction(HER)and oxygen evolution reaction(OER)overpotentials of 262 and 348 mV,respectively.

不同官能团对钙钛矿太阳电池的钝化效果

为了提高钙钛矿太阳能电池的效率和稳定性,许多具有不同官能团的有机分子已被报道用来钝化钙钛矿表面.然而,不同官能团与其钝化效果的内在关联性却很少被人们了解.本文系统研究和比较了12种不同官能团对钙钛矿太阳电池的钝化作用,结果表明,钝化效果和电池的开路电压随着钝化分子与钙钛矿表面缺陷化学键合强度的增加而具有增加趋势.并且其中四叔丁基苯甲酸可以通过分子间的额外氢键作用,形成具有不溶于水和高熔点的晶体界面层,可以进一步稳定钙钛矿薄膜表面的钝化效果.得益于与钙钛矿的强配位作用和自身的氢键作用,基于四叔丁基苯甲酸钝化的钙钛矿电池获得了21.46%效率.更重要的是,这些器件在45%相对湿度下储存了1年以上(10,080小时),仍能保持88%的初始性能.该工作对于理解钙钛矿表界面的钝化以及进一步提高钙钛矿太阳电池性能和稳定性具有积极借鉴意义.

Targeted bottom-up synthesis of 1T-phase MoS2 arrays with high electrocatalytic hydrogen evolution activity by simultaneous structure and morphology engineering

The incorporation of small guest molecules or ions by bottom-up hydrothermal synthesis has recently emerged as a promising new way to engineer 1T-phase MoS2 with high hydrogen evolution reaction （HER） activity. However, the mechanism of the associated structural evolution remains elusive and controversial, leading to a lack of effective routes to prepare 1T-phase MoS2 with controlled structure and morphology, along with high purity and stability. Herein, urea is chosen as precursor of small molecules or ions to simultaneously engineer the phase （16.4%, - 69.4%, and -90.2% of 1T phase） and size （98.8, - 151.6, and - 251.8 nm for the 90.2% 1T phase） of MoS2 nanosheets, which represent an ideal model system for investigating the structural evolution in these materials, as well as developing a new type of 1T-phase MoS2 arrays. Using reaction intermediate monitoring and theoretical calculations, we show that the oriented growth of 1T-phase MoS2 is controlled by ammonia-assisted assembly recrystallization, and stabilization processes. A superior HER performance in acidic media is obtained, with an overpotential of only 76 mV required to achieve a stable current density of 10 mA.cm-2 for 15 h. This excellent performance is attributed to the unique array structure, involving well-dispersed, edge-terminated, and high-purity 1T-phase MoS2 nanosheets.