Public defence, Engineering Physics, MSc Jiali Sheng

Title of the thesis: Sub-nanometer engineering of transition-metal layered hydroxide electrocatalysts

Thesis defender: Jiali Sheng 
Opponent: Professor Hermenegildo García Gómez, Universitat Politècnica de València, Spain
Custos: Aalto Distinguished Professor Olli Ikkala, Aalto University School of Science

Hydrogen produced from water using renewable electricity could help store energy from sources such as wind and solar power. Making this process efficient requires electrocatalysts—materials that accelerate the reactions that split water into hydrogen and oxygen. 

Knowing which catalyst structures work well is one challenge. Understanding what shapes those structures as they form is another. Understanding how catalyst structures are established during synthesis is also important for gaining greater control over their preparation. This doctoral dissertation therefore asks what happens while a catalyst is being formed: how can synthesis-stage variables shape its structural state? 

Using layered hydroxide electrocatalysts, the research explored this question through three complementary studies. First, differences in MXene surface chemistry were associated with changes in hydroxide nucleation and domain development. MXene surfaces with fewer O-containing terminations were associated with smaller cobalt–iron hydroxide structural domains, and the resulting catalysts showed high oxygen evolution activity and long-term stability. Second, MXene participated chemically during cobalt hydroxide formation. Its transformation during synthesis was associated with the retention of a more Co(II)-rich hydroxide state and improved hydrogen evolution behavior. Third, nickel incorporation altered both the structural ordering and local electronic structure of the material, reducing longer-range ordering while preserving the local layered structure. These changes were accompanied by higher intrinsic oxygen evolution activity. 

Together, the three studies show that different synthesis-stage variables can shape distinct structural states in layered hydroxide electrocatalysts, and these states are linked to subsequent catalytic behavior. 

The work therefore expands the question from “Which catalyst structure works?” to also “What shapes that structural state as the catalyst forms?” In the longer term, understanding how these structural states are formed could enable more deliberate control over catalyst synthesis and help bridge the gap between laboratory materials and practical water electrolysis technologies.

Keywords: layered (double) hydroxides, OER, HER, MXenes, electrocatalysts

Thesis available for public display 7 days prior to the defence at Aalto University's public display page. 

Contact Information: 
jiali.sheng@aalto.fi