Can I use potassium bicarbonate instead? NO! You can combine both, but from a physiological standpoint it does not makes sense to increase your serum potassium levels before a workout, because especially strength training will leech potassium from the cells into the blood anyways. Moreover your body conserves potassium pretty well during a workout, while you lose a comparably large amount of sodium in your sweat. In other words, you risk offsetting the peculiar balance of the extra-cellular sodium ions and the intracellular potassium ions. While weakness or skeletal muscle hyperexcitability would be rather harmless, but certainly ergolytic consequences, this can - in the worst case - lead to bradycardia (=abnormally slow heartbeats), arrhythmias and even sudden cardiac arrest as it was observed in the two "salt-phobic" bodybuilders in the case report I already cited in the comments on the "Sodium Bicarbonate for High Volume Strength Training" post (cf. John. 2011; there were probably confounding factors at play, here, but still, the risk of developing hyperkalemia is nothing you can totally exclude, if you ingest tons of potassium within a couple of minutes).
If you feel that you don't get enough potassium in your diet, anyway, I'd suggest you mix them at a 3:1 ratio as you usually see it for "normal" sodium and potassium in electrolyte products.
