The geometry of additively manufactured nickel electrodes influences the selectivity of glycerol electrooxidation. An increased surface area at zero depth correlates with higher selectivity for C₂ and C₃ products, as well as improved Faradaic efficiency. Glycerol conversion increases by enhancing the nominal geometric area through the introduction of grids on the surface, shifting the selectivity towards formic acid.

Electrocatalytic selectivity is generally explained in terms of atomic-scale properties, i.e., active sites, overlooking the impact of macroscopic electrode geometry and structure, which affect the macroscopic mass transport. This study demonstrates how the geometry of additively manufactured (AM) nickel electrodes fabricated via laser powder bed fusion influences reaction selectivity and the conversion rate of the glycerol oxidation reaction. All six AM electrodes with different geometries exhibit formic acid selectivity above 80%, with the large grid electrode achieving 95%. The large grid has deeper cavities and confined structures that promote enhanced oxidation due to restricted diffusion of C₂ and C₃ intermediates toward the bulk of the solution. The highest glycerol conversion of 28.2% is achieved with a 99% carbon balance, confirming efficient mass utilization. While achieving 100% formic acid yield remains challenging, minor byproducts are limited to ≤5%. These results emphasize that electrode geometry can be strategically tailored to optimize selectivity and enhance conversion efficiency. The significance of structural effects in electrocatalytic reactions is highlighted, providing novel insights into electrode design.