Topotactical Hydrogen Induced Single-Band d-Wave Superconductivity in La_{2}NiO_{4}

La_{2}NiO_{4} is an antiferromagnetic insulator with a structural resemblance to its cuprate counterpart, La_{2}CuO_{4}. However, La_{2}CuO_{4} has a Cu^{2+} or 3d^{9} electronic configuration that needs to be hole or electron doped for superconductivity, whereas La_{2}NiO_{4} is 3d^{8} with divalent Ni^{2+}. Making a cuprate analog through conventional electron doping is impractical due to the rarity of tetravalent substituents for trivalent La. Here, we propose an alternative route: intercalating topotactical hydrogen, which is possible through electric-field-controlled protonation and transforms La_{2}NiO_{4} into a 3d_{x^{2}-y^{2}} single-band two-dimensional antiferromagnetic Mott insulator analogous to La_{2}CuO_{4}. This we find through density-functional theory and dynamical mean-field theory calculations. The furthergoing dynamical vertex approximation predicts that H-La_{2}NiO_{4} can host d-wave superconductivity under 15% hole doping with a critical temperature above 20 K. Our findings not only suggest a new method for tuning the electronic structure of layered nickelates but also provide theoretical evidence for a new nickelate superconductor, awaiting experimental synthesis.